| 1. |
- Cronander, C., et al.
(författare)
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Closed loop roll control using aeroelastic information
- 2000
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Ingår i: Aerospace Science and Technology. - 1270-9638 .- 1626-3219. ; 4:7, s. 481-494
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical model of the rolling dynamics of a flexible wing is derived by experimental measurements and 3D potential flow analysis. Based on the mathematical model which includes one aeroelastic parameter, control laws are designed which almost completely eliminate the problem of reduced aileron efficiency for increasing airspeed. Finally, the control laws are tested on the model in the wind tunnel, and good correlation with computer simulations is achieved, except when a structural mode is excited.
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| 2. |
- Girodroux-Lavigne, P., et al.
(författare)
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Comparison of static and dynamic fluid-structure interaction solutions in the case of a highly flexible modern transport aircraft wing
- 2003
-
Ingår i: Aerospace Science and Technology. - 1270-9638 .- 1626-3219. ; 7:2, s. 121-133
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the computational work performed by five of the fifteen partners in the Brite-Euram project UNSI, for the prediction of static aeroelastic configurations and dynamic flutter response at transonic conditions, using advanced time-domain fluid-structure coupling methods. The aerodynamic models, mechanical models, and coupling strategies implemented in the different solvers are presented. A code to code validation of the fluid-structure coupled solvers has been achieved in the case of the highly flexible MDO wing. The coupled codes have each been used first for the computation of steady state flow and static deformations at different flight conditions. The investigation of flutter has been carried out for off-design, heavy-cruise flight conditions, using time-consistent numerical simulations. Dynamic responses have been recorded and compared for stable and flutter conditions. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
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| 3. |
- Haggmark, C. P., et al.
(författare)
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A numerical and experimental study of a transitional separation bubble
- 2001
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Ingår i: Aerospace Science and Technology. - 1270-9638 .- 1626-3219. ; 5:5, s. 317-328
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Tidskriftsartikel (refereegranskat)abstract
- A combined numerical and experimental study of a two-dimensional transitional separation bubble due to an adverse pressure gradient is reported. The experiments have been performed in the MTL wind tunnel with a contoured wall imposing an adverse pressure gradient on the flow over a flat plate. The separated shear-layer is highly unstable and transition to turbulence occurs in the flow. The experimental separation bubble flow is modelled numerically using two-dimensional direct numerical simulations (DNS). Prescribing free stream boundary conditions in the wall normal velocity the experimental bubble is reproduced. The development of artificially forced two-dimensional instability waves is investigated and good agreement is found between experiments, simulations and linear stability theory (LST). The performance of several engineering transition prediction methods applied on the present separation bubble is presented and compared. Methods based on simplifications of the e(n)-method yield predictions in accordance with experiments and DNS.
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| 4. |
- Young, T., et al.
(författare)
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Durability of hybrid laminar flow control (HLFC) surfaces
- 2003
-
Ingår i: Aerospace Science and Technology. - 1270-9638 .- 1626-3219. ; 7:3, s. 181-190
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Tidskriftsartikel (refereegranskat)abstract
- As a part of the European Commission sponsored HYLTEC (Hybrid Laminar Flow Technology) project, a SAAB 2000 aircraft - fitted with a number of small laser drilled panels on the wing leading edge - completed 20 months of routine service, the objective being to investigate contamination and durability aspects of Hybrid Laminar Flow Control (HLFC) suction surfaces. A post-flight test investigation of these panels, manufactured from Nd-YAG laser drilled titanium, aluminium and carbon fibre polyetheretherketone (PEEK) composite, has been conducted. Using Scanning Electron Microscopy (SEM), evidence of corrosion and damage was investigated. An optical inspection technique was used to measure hole geometries and the results were compared to pressure loss measurements through the panels. Titanium was found to be the most robust material, displaying no adverse affect from this exposure, whilst aluminium was found to be substantially less durable. The PEEK carbon fibre composite showed signs of surface degradation after only two months of flight trials. © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
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| 5. |
- Ahn, Myeonghwan, et al.
(författare)
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A numerical study on near-field pressure fluctuations of symmetrical and anti-symmetrical flapping modes of twin-jet using a high-resolution shock-capturing scheme
- 2021
-
Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; , s. 107147-107147
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Tidskriftsartikel (refereegranskat)abstract
- Screeching supersonic jets appears at off-design operating conditions and is perceived as an intense tonal noise. In a twin nozzle configuration, mutual interactions between the two jet plumes may occur with various coupling modes developing depending on the operating conditions and lateral distance between the jets. The investigation of the detailed flow behaviors and near-field pressure fluctuations with relevance to the twin jets system, the analysis of the developed instabilities, will enhance understanding of fundamental features associated with jets located close to each other.In the present study, the single jet is considered first to assess the large eddy simulation (LES) approach used and the near-field pressure fluctuation predictions. Based on the validated solver, twin jets are simulated. Two different twin-nozzle configurations having different separation distance or nozzle-to-nozzle centerline spacing are scrutinized for the same Mach number of 1.358. Notably, the twin jets are screeching by the coupling mode for both set-ups; however, the case of closer inter-nozzle distance presents a symmetrical dominant flapping mode, while the other case shows an anti-symmetrical flapping mode. The strength of the pressure fluctuation at the fundamental frequency changes depending on the location of the observer point (upstream or downstream) and the reference plane (twin-jet and normal to the twin-jet plane). The screech tones of the two cases, observable in the upstream region, are significantly different in the normal to the twin-jet plane direction because of the phase difference of fluctuating pressure. However, the first harmonic component remains strong, regardless of the flapping mode. It is also observed that, at the fundamental frequency, the amplitude of the pressure fluctuation at downstream locations is found to be strong in the normal to the twin-jet plane when the symmetrical flapping mode occurs. This feature is also observed in the twin-jet plane in the case of the opposite mode. By analyzing the developed vertical structures and performing correlation analyses of pressure fluctuations along jet shear layers, the periodicity of the flow in the downstream region with relevance to the fundamental frequency is revealed.
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| 6. |
- Alepuz, Javier Pérez, et al.
(författare)
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Direct image-based visual servoing of free-floating space manipulators
- 2016
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 55, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an image-based controller to perform the guidance of a free-floating robot manipulator. The manipulator has an eye-in-hand camera system, and is attached to a base satellite. The base is completely free and floating in space with no attitude control, and thus, freely reacting to the movements of the robot manipulator attached to it. The proposed image-based approach uses the system's kinematics and dynamics model, not only to achieve a desired location with respect to an observed object in space, but also to follow a desired trajectory with respect to the object. To do this, the paper presents an optimal control approach to guiding the free-floating satellite-mounted robot, using visual information and considering the optimization of the motor commands with respect to a specified metric along with chaos compensation. The proposed controller is applied to the visual control of a four-degree-of-freedom robot manipulator in different scenarios.
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| 7. |
- Andersson, Kent, 1967-
(författare)
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Modeling the impact of surface emissivity on the military utility of attack aircraft
- 2017
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Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 65, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- An analysis scheme and a mission system model were applied to the evaluation of the military utility of efforts to reduce infrared signature in the conceptual design of survivable aircraft. The purpose is twofold: Firstly, to contribute to the development of a methodological framework for assessing the military utility of spectral design, and secondly to assess the threat from advances in LWIR sensors and their use in surface-to-air-missile systems. The modeling was specifically applied to the problem of linking the emissivity of aircraft coatings to mission accomplishment. The overall results indicate that the analysis scheme and mission system model applied are feasible for assessing the military utility of spectral design and for supporting decision-making in the concept phase. The analysis of different strike options suggests that LWIR sensors will enhance the military utility of low emissive paint, at least for missions executed in clear weather conditions. Furthermore, results corroborate and further clarify the importance of including earthshine when modeling.
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| 8. |
- Berggren, Daniel
(författare)
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Investigation of limit cycle oscillations for a wing section with nonlinear stiffness
- 2004
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 8:1, s. 27-34
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Tidskriftsartikel (refereegranskat)abstract
- A wind tunnel experiment is designed with the objective to obtain well-behaved limit cycle oscillations for a wing section with two degrees of freedom, translation and rotation, in two-dimensional flow. This is accomplished using a setup of linear springs so that the resulting moment is a nonlinear function of the rotation angle. The experimental setup is designed so that the amplitudes of the limit cycle oscillations are sufficiently low to motivate the use of linear aerodynamics in the analysis. The experimental results are compared to analyses for two different configurations, and the agreement is fairly good.
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| 9. |
- Bravo-Mosquera, P. D., et al.
(författare)
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Conceptual design and CFD analysis of a new prototype of agricultural aircraft
- 2018
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Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 80, s. 156-176
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Tidskriftsartikel (refereegranskat)abstract
- In the agricultural aviation, there are several aerodynamic factors that must be optimized in order to contribute to the successful application of agricultural products, such as the high aerodynamic efficiency (L/D) required at the working phase and the influence of aircraft wingtip phenomena on the spray deposition and movement. For these reasons, in this research is presented the conceptual design of an advanced prototype of agricultural aircraft, whose main characteristic is an adaptive multi-winglet device installed on the wingtips, which optimized the main aerodynamic issues presented in its mission. Traditional aircraft design methods were used to develop and assess the suitability of the aircraft, focusing on its design requirements and tackling studies of weight sizing, pilot ergonomics, aerodynamics, stability, and performance. Subsequently, analytical and computational methods were used to design the adaptive multi-winglet device, which is composed by three winglets with its own geometry fitted on a tip-tank. Six configurations were created by modifying only the cant angle of each winglet in order to determine the arrangement that provides the best aerodynamic characteristics through a study of computational fluid dynamics (CFD), using the Reynolds–Averaged–Navier–Stokes (RANS) equations coupled with the Shear Stress Transport (SST) turbulence model. First, the flow around the wing and the multi-winglet section of the aircraft was investigated exclusively. Afterward, the airflow around the entire aircraft was studied at the product application condition, in order to compare the overall aerodynamic performance of the baseline concept along with the optimal multi-winglet configuration installed on the aircraft. Lift, drag and pitching moment coefficients were assessed, as well as the wingtip vortex structure of the most relevant configurations. Results of this study showed that adaptive multi-winglet devices are a promising alternative to improve the overall performance of an agricultural aircraft, because they provide control over the size and strength of the wake-spray interaction on the sprayed product, reduce the induced drag, reduce the bending moment and improve the aerodynamic efficiency of the aircraft.
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| 10. |
- Carlsson, Martin, et al.
(författare)
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Efficient roll control using distributed control surfaces and aeroelastic effects
- 2005
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 9:2, s. 143-150
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Tidskriftsartikel (refereegranskat)abstract
- The potential of using multiple leading and trailing edge control surfaces and aeroelastic effects for efficient roll manoeuvring is investigated. Numerical optimization in combination with a simulation model including aeroelastic dynamics is used to design a controller for roll angle tracking. The controller distributes the control power to the individual surfaces such that it minimizes the control effort yet fulfilling roll performance requirements in a wide airspeed envelope. The controller is implemented and experimentally validated using an elastic wind-tunnel model equipped with 16 individual control surfaces. Good correlation between simulations and experiments is obtained although some deviations are observed and discussed. Finally, the choice of the most efficient control surface layout is investigated by evaluating control laws which utilize a subset of the available control surfaces.
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| 11. |
- Chen, Song, et al.
(författare)
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Flow and aeroacoustic attributes of highly-heated transitional rectangular supersonic jets
- 2021
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 114:106747
-
Tidskriftsartikel (refereegranskat)abstract
- Heated transitional supersonic jets exhausting from a rectangular nozzle at over-expanded conditions are investigated by Large Eddy Simulations and Ffowcs-Williams and Hawkings acoustic analogy. Four cases with a fixed nozzle pressure ratio but different temperature ratios (TR) of 1.0, 2.0, 4.0, and 7.0 are analyzed. Numerical results show that with the increasing temperature the jet velocity significantly increases, whereas its Reynolds number decreases by about one order of magnitude, which leads to a 30% decrease in the jet potential core length and reduction in the number of shock cells. The increasing temperatures also result in supersonic shear layer convection Mach numbers and consequently Mach wave radiations in the acoustic fields. Pressure skewness and kurtosis factors indicate crackle noise and non-linear propagation effects in high temperatures. For the most heated jet TR 7.0, the Mach wave radiation is identified radiating noise at about 120 degrees, while the large turbulence structure noise at about 150 degrees. Furthermore, the vortex sheet model analysis and the LES data detect the existence of upstream-propagating neutral waves inside jet TR 7.0. The observed screech frequency falls within the range of antisymmetric mode indicating that the highly-heated jet is characterized by an antisymmetric oscillation mode at the screech frequency.
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| 12. |
- Chen, Song, et al.
(författare)
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Numerical study of non-reacting flowfields of a swirling trapped vortex ramjet combustor
- 2018
-
Ingår i: Aerospace Science and Technology. - : Elsevier Masson SAS. - 1270-9638 .- 1626-3219. ; 74, s. 81-92
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Tidskriftsartikel (refereegranskat)abstract
- In this work, 3D numerical investigations of a trapped vortex combustor operated in different swirling flow conditions are performed by solving Reynolds-averaged Navier-Stokes equations with Reynolds-stress model. Emphasis is placed on the non-reacting flowfield characteristics and the stability of the locked vortex. Validation is performed first by comparing the present results with experimental data available. It shows that the Reynolds-stress model can provide good predictions for flows with a swirl number up to 0.98. It is also found that the cavity vortex can be trapped well in flows with different swirl numbers. To further study the "locked" vortices, flow disturbances are introduced to the trapped vortex combustor via suddenly increasing swirl number from 0.6 to 0.98. The transient simulation results reveal that the cavity vortex is highly resistant to the flow disturbances and is still well trapped in the cavity, while vortex shedding of the conventional breakdown vortex is observed in the presence of the flow disturbances. Turbulence intensity and kinetic energy are found to be significantly increased by approximately 300%, which indicates that the fuel-air mixing can be dramatically improved. This study shows that the swirling trapped vortex combustor is an alternative promising robust and efficient combustor concept.
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| 13. |
- Chen, Song, et al.
(författare)
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RANS investigation of the effect of pulsed fuel injection on scramjet HyShot II engine
- 2019
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 84, s. 182-192
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Tidskriftsartikel (refereegranskat)abstract
- Effective and efficient fuel-air mixing plays a critical role in the successful operation of scramjet engines. To enhance the fuel-air mixing in supersonic combustion systems with a short flow residence time, the pulsed fuel injection strategy in a realistic scramjet combustor flow condition provided by the HyShot II is numerically studied in this work. For this, 2D and 3D simulations of the hydrogen fueled HyShot II scramjet with pulsed fuel injections are performed. Emphasis is placed on the cold flow field characteristics and fuel-air mixing performance in the combustor. Reynolds-Averaged Navier-Stokes equations are solved with the implementation of the two equation k-omega SST turbulence model via using the ANSYS FLUENT v17.1. The pulsed fuel injection is numerically achieved by implementing a time-dependent total pressure pulse with the shape of a square wave. The total pressure peak is maintained as same as the one that chokes the fuel injector in steady operations. The numerical model is validated first by comparing the results with the experimental data available in the literature. It is then used to study the effect of the pulse injection with different frequencies. It is found that complicated waves structures are formed inside the fuel injector in pulsed fuel injections due to the total pressure pulse. These waves propagate outside the fuel injector and lead to the fuel streams with wavy patterns and the unsteady shock structures in the combustion chamber. Fuel penetration depths are not found to be increased for pulsed injections in this study, but much high turbulent kinetic energy (TKE) levels are observed especially inside the fuel injector. With the help of increased TKE, mixing efficiency is found to be improved for all of the pulsed fuel injection by up to 30%. This mixing improvement also strongly depends on the frequency applied. 2018 Elsevier Masson SAS. All rights reserved.
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| 14. |
- Ericsson, Andreas, et al.
(författare)
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A combined electromagnetic and acoustic analysis of a triaxial carbon fiber weave for reflector antenna applications
- 2016
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Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 58, s. 401-417
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Tidskriftsartikel (refereegranskat)abstract
- Fiber composites are widely used for space applications such as antennas, solar panels and spacecraft support structures. This paper presents a combined electromagnetic and acoustic analysis of a triaxial carbon fiber weave structure, designed for ultra lightweight reflector antennas in satellite communication systems. The electromagnetic and acoustic performance of the structure are analyzed over a wide range of parametric studies, both at a microscopic and mesoscopic length scale. The electromagnetic study indicates that the main parameter governing the electromagnetic reflection performance of the weave is the electric conductivity of the carbon fibers, given that the weave structure is significantly smaller than the wavelength of the incident signals. The acoustic study identifies a critical threshold in the mesoscale geometry in order to avoid a critically high resistive behavior of the weave structure, driven by viscous effects. Design guidelines are drawn from these analyses in order to achieve a trade-off between the electromagnetic reflection properties and the resistance to acoustic loading of such composite materials. These combined analyses allow to deepen the understanding from both an electromagnetic and acoustic perspective in order to open for some new design possibilities.
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| 15. |
- Felicetti, Leonard, 1982-, et al.
(författare)
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Image-based attitude maneuvers for space debris tracking
- 2018
-
Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 76, s. 58-71
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes an image-based control scheme for tracking space debris using onboard optical sensors. The proposed strategy uses an onboard camera for detecting space debris. The camera is rigidly attached to the satellite; therefore specific attitude maneuvers need to be performed during different phases of the mission. First, the spacecraft orients its attitude to point the camera toward a fixed direction in space, and then when debris traces streak across the field of view of the camera, the spacecraft follows and tracks the motion of the debris. Finally, a disengagement maneuver is executed to stop the spacecraft rotation when the debris disappears from the camera field of view. The model and the developed control scheme take into account the typical characteristics of space-qualified cameras, and a Kalman filter is developed to reduce the effects of the camera noise, detect and predict the path of the debris in the image plane, and estimate the angular velocity of the spacecraft. The entire estimation/control scheme is then validated through numerical simulations, using a model of reaction wheels as the main attitude actuation system. The results demonstrate the viability of such maneuvers in a typical space debris surveillance mission scenario.
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| 16. |
- Felicetti, Leonard, et al.
(författare)
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Nanosatellite swarm missions in low Earth orbit using laser propulsion
- 2013
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 27:1, s. 179-187
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Tidskriftsartikel (refereegranskat)abstract
- Many missions could benefit from the exploitation of very low height orbits, including Earth observation, atmospheric measurement and space weather research missions. However satellite's lifetime decreases very quickly when the mission requires to orbit into the dense layers of the atmosphere. The mission performance could be enhanced using innovative propulsion techniques, counteracting the effect of atmospheric drag. Among these, laser propulsion potentially offers great weight and power savings, obtained by separating the propulsion system energy source from the propelled satellite. The energy source for the propulsion system is a pulsed laser beam generated remotely, while only collecting mirrors and ablative material are necessary on the target spacecraft. A mission architecture for very low altitude nanosatellite swarms using a space-based pulsed laser propulsion is described. A simplified laser-sustained re-orbiting maneuver sequence is proposed, leading to a straightforward evaluation of the maneuver times, showing that the laser propulsion system is suitable for low altitude nanosatellite missions
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| 17. |
- Felicetti, Leonard, et al.
(författare)
-
Three spacecraft formation control by means of electrostatic forces
- 2016
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 48, s. 261-271
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on electrostatic orbital control in formation flying by using switching strategies for charge distribution. Natural and artificial charging effects are taken into account, and limits in charging technology and in power requirements are also considered. The case of three spacecraft formation, which is intrinsically different and more difficult than the two spacecraft problem often analyzed in literature, has been investigated. A Lyapunov based global control strategy is presented and applied to perform formation acquisition and maintenance maneuvers, producing as output the required overall charge. Then, a selective and optimized charge distribution process among the satellites is discussed for avoiding charge breakdowns to surrounding plasma, for reducing the power requirements and the number of charge switches. The results of numerical simulations show the advantages and drawbacks of the selected control technique
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| 18. |
- Franke, M., et al.
(författare)
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Assessment of explicit algebraic Reynolds-stress turbulence models in aerodynamic computations
- 2005
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 9:7, s. 573-581
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Tidskriftsartikel (refereegranskat)abstract
- In the aerodynamic industrial design process, the use of numerical simulation, including viscous effects, is of ever increasing importance. As simple, standard Boussinesq-viscosity turbulence models have proven insufficient to correctly predict complex flow situations, attention is drawn to more reliable approaches towards the modelling of turbulence. This work aims at assessing the potential of Explicit Algebraic Reynolds Stress Models (EARSM) for application-oriented aerodynamic computations. To this end, two different EARSM are investigated on a variety of configurations in sub- and transonic steady flow, ranging from 2D aerofoils to 3D wing/body-configurations. Is is demonstrated that an increased over-all simulation quality is achieved. Thus, while their overhead with respect to standard linear approaches remains limited, EARSM constitute a valuable extension to the model range available to the aerodynamic design engineer.
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| 19. |
- Frink, N. T., et al.
(författare)
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Collaborative study of incipient separation on 53°-swept diamond wing
- 2016
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Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 57, s. 76-89
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Tidskriftsartikel (refereegranskat)abstract
- A systematic analysis of incipient separation and subsequent vortex formation from moderately-swept blunt leading edges is presented for a 53°-swept diamond wing. This work contributes to a collective body of knowledge generated within the multinational NATO/STO AVT-183 Task Group titled "Reliable Prediction of Separated Flow Onset and Progression for Air and Sea Vehicles". Details of vortex formation are inferred from numerical solutions of two flow solvers after establishing a good correlation of the global flow field and surface pressure distributions with those from wind tunnel measurements. From this, significant and sometimes surprising insights into the nature of incipient separation and part-span vortex formation are derived from the wealth of information available in the computational solutions.
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| 20. |
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| 21. |
- Göransson, Peter
(författare)
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Tailored acoustic and vibrational damping in porous solids - Engineering performance in aerospace applications
- 2008
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 12:1, s. 26-41
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Tidskriftsartikel (refereegranskat)abstract
- A porous solid, saturated with fluid, may be described as an elastic-viscoelastic and acoustic-viscoacoustic medium. The transport of vibroacoustic energy is carried both through the sound pressure waves propagating through the fluid in the pores, and through the elastic stress waves, carried through the solid frame of the material. For most porous materials, used to reduce sound and vibration, these waves are coupled to each other, i.e. they simultaneously propagate in both the fluid and the solid frame but with different strengths. A characteristic of this coupled wave propagation, is that the vibroacoustic energy is dissipated and converted into heat as the wave travels through the material. Clearly for a given situation, the balance between energy dissipated through vibration of the solid frame and changes in the acoustic pressure varies with the topological arrangement, choice of material properties, interfacial conditions, etc. This paper illustrates the influence such a balancing has on the performance of a multi-layer sound proofing arrangement applicable for an aircraft interior.
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| 22. |
- Hakima, Houman, et al.
(författare)
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Concurrent attitude and orbit control for deorbiter CubeSat
- 2020
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Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 97
-
Tidskriftsartikel (refereegranskat)abstract
- This paper details a concurrent attitude and orbit control method for a debris-removing nanosatellite, called deobriter CubeSat, during the rendezvous and synchronization maneuver with an uncontrollable tumbling debris object. The CubeSat is designed based on the utilization of an eight-unit form factor and commercially-available components with substantial space heritage, and is intended for the removal of sizable debris objects in low-Earth orbit. In particular, a low-thrust propulsion system is used for orbit control, as well as three reaction wheels allowing for a three-axis attitude control. Since the thruster can only produce force in one direction in the body frame, the spacecraft is considered to be underactuated. The controller employs the reaction wheels and the thruster to simultaneously rendezvous and synchronize the attitude of the CubeSat with the tumbling debris object, allowing for a concurrent attitude and position tracking. Detailed derivation of the concurrent controller is discussed, the effects of high-order derivatives are analyzed, and the stability of the system is proved. Simulation scenarios are created for two different thruster operation modes, namely, unsaturated thrust force and continuously-saturated thrust force, in order to verify the performance of the controller, as well as its robustness against gravity gradient disturbance torque and gravitational perturbation force.
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| 23. |
- Jacobsen, Marianne, 1980-
(författare)
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Real time drag minimization using redundant control surfaces
- 2006
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 10:7, s. 574-580
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Tidskriftsartikel (refereegranskat)abstract
- A method for minimizing the drag of a wind tunnel model with multiple control surfaces is presented. The minimization is performed in the wind tunnel and measurements are performed in real time. Real time measurements introduce difficulties such as noise in the signals, hysteresis and problems with repeatability of the function evaluations. The lack of a numerical function to minimize therefore puts certain demands on the optimization method, and hence a derivative free method, often referred to as a generating set search method, is used. The proposed method is generalized to take both linear equality constraints as well as linear inequality constraints into account. The generating set search method is implemented in the wind tunnel and tests show that the drag can be decreased while satisfying the constraints.
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| 24. |
- Jacobsen, Marianne, 1980-, et al.
(författare)
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Reducing emissions using aircraft trajectory optimization
-
Ingår i: Aerospace Science and Technology. - 1270-9638 .- 1626-3219.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Optimal aircraft trajectories reducing engine emissions are computed using numerical optimization. The emissions from the jet engine are modeled as functions of the aircraft altitude, airspeed and throttle setting. Combining the emission models with a performance model of the aircraft, the optimization problem is formulated with the objective of reducing emissions for a given distance flight. The resulting problem, involving a system of differential and algebraic equations, is discretized using collocation and the optimization problem is solved using sequential quadratic programming. Different objectives are investigated, such as minimizing the total emissions of carbon dioxide, carbon monoxide, oxides of nitrogen and hydrocarbons during a flight. Methods from life cycle impact assessment are used to weigh the different emissions to an index and several different indices are used and compared. A model of the Boeing 737-600 is used to illustrate the developed optimization method. The results show that the trajectories differ significantly depending on the chosen objective. Using a combination of objectives at different altitudes may give the most appropriate problem formulation.
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| 25. |
- Kapidzic, Zlatan, 1978-, et al.
(författare)
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Conceptual studies of a composite-aluminum hybrid wing box demonstrator
- 2014
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Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 32:1, s. 42-50
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of two different hybrid composite-aluminum concepts applied to a winglike structure which is exposed to mechanical and thermal load. The aim of the study is to determine the most suitable hybrid concept to later on be used in structural fatigue and static testing. In both concepts, the mass is optimized with respect to two different sets of requirements, one of which is currently in use in the fighter aircraft industry and one which is a modified version of the current requirement set. The issues considered in the study are mass, thermal behavior, buckling, bolted joints, failure criteria and fatigue damage, and they are examined in the frame of both requirement sets. The results clearly indicate the order of criticality between the different criteria in the different parts of each concept. Also, the comparison of two requirement sets gives an idea of the degree of influence of the modified criteria on the hybrid concepts and their mass. Based on the mass and the structural behavior in a thermal-mechanical loading one of the hybrid concepts is chosen for further studies and testing.
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| 26. |
- Le Clainche, Soledad, et al.
(författare)
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Improving aircraft performance using machine learning : A review
- 2023
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 138
-
Forskningsöversikt (refereegranskat)abstract
- This review covers the new developments in machine learning (ML) that are impacting the multi-disciplinary area of aerospace engineering, including fundamental fluid dynamics (experimental and numerical), aerodynamics, acoustics, combustion and structural health monitoring. We review the state of the art, gathering the advantages and challenges of ML methods across different aerospace disciplines and provide our view on future opportunities. The basic concepts and the most relevant strategies for ML are presented together with the most relevant applications in aerospace engineering, revealing that ML is improving aircraft performance and that these techniques will have a large impact in the near future.
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| 27. |
- Lim, H.D., et al.
(författare)
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Effects of bevelled nozzles on standoff shocks in supersonic impinging jets
- 2019
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 94
-
Tidskriftsartikel (refereegranskat)abstract
- Moderately under-expanded jets issuing from a circular baseline and two bevelled circular nozzles impinging upon a perpendicular flat plate were experimentally studied. The effects of nozzle-pressure-ratio and separation distance variations on the standoff shock formations were investigated with schlieren visualizations and a visual hull based three-dimensional (3D) shock reconstruction technique to provide deeper insights into their 3D features. Across all flow configurations arising from the different combinations of these parameters, results indicated that the bevelled nozzles are effective in introducing asymmetry to the standoff shock geometries. Depending on the exact flow configuration, standoff shock locations may also undergo significant upstream displacements. In particular, the single-bevelled nozzle produces highly unsteady standoff shocks with asymmetric oscillation amplitudes along both side of the nozzle lip regions. Changes to the standoff shock key characteristics were observed to be sensitive towards the jet shock structures and reflection point modified by the bevelled nozzle exits. In particular, the strength and relative position of the reflection point are identified as the major contributing factors influencing the upstream static pressure distribution of the standoff shock, hence leading to the observed changes in the standoff shock behaviour.
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| 28. |
- Lim, H. D., et al.
(författare)
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Short-time proper orthogonal decomposition of time-resolved schlieren images for transient jet screech characterization
- 2020
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 107
-
Tidskriftsartikel (refereegranskat)abstract
- Short-time Proper Orthogonal Decomposition (POD) is proposed as an image-based technique to study the transient jet screech characteristics of moderately under-expanded supersonic jets emanating from a circular baseline and two bevelled nozzles. Time-resolved schlieren imaging of turbulent flow structures were performed with an ultrahigh-speed schlieren setup. Short-time POD was performed by systematically sampling image-series with a short time delay, performing PODs and applying spectral analyses on the first POD mode coefficients, and plotting the peak frequencies from the resulting PSDs into a peak frequency-occurrence count histogram. The results are in good agreement with the near-field noise spectra and wavelet transform analysis of the microphone measurements, which revealed intermittent jet screech occurrences at St=0.25 for both baseline and 30 degrees bevelled jets, while none was detected for the 60 degrees bevelled jet. In particular, the occurrence counts of the frequency bins is proposed as a suitable parameter to characterize the intermittent nature of jet screech, with the frequency bin revealing the jet screech frequency if present. The present study demonstrates the advantage of short-time POD analysis on time-resolved schlieren images over traditional image-based POD methods, which includes computational gains from parallelization, the ability to handle much larger datasets and revealing insights into a transient flow and noise phenomenon.
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| 29. |
- Majić, Frane, et al.
(författare)
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Potential improvement of aerodynamic performance by morphing the nacelle inlet
- 2016
-
Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 54, s. 122-131
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Tidskriftsartikel (refereegranskat)abstract
- In this work numerical investigations of the aerodynamic performance of an adaptive turbofan-engine inlet is performed. The adaptation is made on the inner front part of the symmetric inlet by changing the positions of two contour knots, which acts as a possible inlet struc- ture morphing. The contour knots are moved in the axisymmetric and radial directions of the inlet, respectively. The numerical calcula- tions are performed using Reynolds Averaged Navier-Stokes (RANS) simulations and are made for climb and cruise flight conditions. The evaluation of the aerodynamic performance is based on the absolute total pressure recovery at the fan plane. The results show that the adaptation of only a small part of the inlet contour gives benefits in the performance at different flight conditions. The radial position in- crease of the knot closer to the leading edge gives overall increase of the pressure recovery level for both flight conditions. The radial posi- tion change of the knot close to the throat diameter leads to the global maximum of absolute total pressure recovery almost independent of the axial position change of the same knot, for both flight conditions. These maximums are attained at different radial positions of the knot close to the throat diameter, for the two flight conditions.
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| 30. |
- Marcus, Carina
(författare)
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Aspects of the design, evaluation and accuracy of airborne sensor clusters using time-difference of arrival
- 2019
-
Ingår i: Aerospace Science and Technology. - : ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER. - 1270-9638 .- 1626-3219. ; 92, s. 892-900
-
Tidskriftsartikel (refereegranskat)abstract
- One way of improving situational awareness without increasing the risk of detection is to use passive sensor systems. If this capability is provided by several aircraft in a cluster, which can incorporate small basic sensor platforms, advantages can be gained such as longer baselines and an increased number of sensors in the cluster. In this paper, a methodology is presented that links results from signal processing to a Design Space Exploration, DSE, regarding sensor clusters when designing clusters that can operate both independently and in cooperation with other systems. When using Time-Difference of Arrival, the accuracy of the estimated location of a signal source depends on errors in timing and positioning of the sensors, errors in estimating signal arrival times and number of sensors and their spatial distribution. The Cramer-Rao Lower Bound is used to investigate the accuracy of signal source estimates for five different clusters and two levels of timing and positioning accuracy. The results show that the direction of arrival estimates are more accurate than those for the range. Although more sensors generally increased the accuracy, their spatial distribution and baseline related to the distance to the signal source also influence the quality of the results. The DSE process is supported by the collected presentation of the data regarding the measurement accuracy of the different sensor configurations, incorporating both cluster configuration as well as the positioning and timing. Having readily accessible data, the decision makers can focus on choosing the sensor system that meets the operational needs. (C) 2019 Elsevier Masson SAS. All rights reserved.
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| 31. |
- Marcus, Carina, et al.
(författare)
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Balancing the radar and long wavelength infrared signature properties in concept analysis of combat aircraft – A proof of concept
- 2017
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 71, s. 733-741
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Tidskriftsartikel (refereegranskat)abstract
- Designing combat aircraft with high military effectiveness, affordability and military suitability requires balancing the efforts of many engineering disciplines during all phases of the development. One particular challenge is aircraft survivability, the aircraft's ability to avoid or withstand hostile actions. Signature management is one way of increasing the survivability by improving the ability to avoid detection. Here, the long-wave infrared and radar signatures are studied simultaneously in a mission context. By establishing a system of systems approach at mission system level, the risk of sub optimization at a technical level is greatly reduced. A relevant scenario is presented where the aim is to incapacitate an air-defense system using three different tactics: A low-altitude cruise missile option, a low and medium altitude combat aircraft option. The technical sub-models, i.e. the properties of the signatures, the weapons and the sensors are modeled to a level suitable for early concept development. The results from the scenario simulations are useful for a relative comparison of properties. Depending on the situation, first detection is made by either radar or infrared sensors. Although the modeling is basic, the complexity of the infrared signature and detection chain is demonstrated and possible pivot points for the balancing of radar and IR signature requirements are identified. The evaluation methodology can be used for qualitative evaluation of aircraft concepts at different design phases, provided that the technical models are adapted to a suitable level of detail.
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| 32. |
- Mendenhall, M.R., et al.
(författare)
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Comparing and benchmarking engineering methods for the prediction of X-31 aerodynamics
- 2012
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 20:1, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- A number of useful engineering methods are available for fast and economic estimates of the aerodynamic characteristics of complex flight vehicles. This article investigates the application of three specific engineering methods to the X-31 fighter configuration, and CFD, wind tunnel, and flight test data are used for comparison and evaluation purposes. The emphasis is on static longitudinal stability aspects up to high angles of attack; however, selected asymmetric and unsteady effects are considered. Results from the engineering methods are in good agreement with experiment and CFD for angles of attack up to 15° for most cases and higher angles for some cases. Results for pitching moment are in good agreement with CFD, but many of the nonlinear characteristics of the airplane are not predicted by the engineering methods. The quality of the longitudinal stability results is discussed in terms of the prediction of the center of pressure on the vehicle. The results provide improved understanding of the continued usefulness of engineering methods as an analysis tool during the design phase and into the flight test diagnostic phase of a new aircraft.
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| 33. |
- Niemi, Antti, et al.
(författare)
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On the shape optimization of flapping wings and their performance analysis
- 2014
-
Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; , s. 274-292
-
Tidskriftsartikel (refereegranskat)abstract
- The present work is concerned with the shape optimization of flapping wings in forward flight. The analysis is performed by combining a gradient-based optimizer with the unsteady vortex lattice method (UVLM). We describe the UVLM simulation procedure and provide the first methodology to select properly the mesh and time-step sizes to achieve invariant UVLM simulation results under mesh refinement. Our objective is to identify a set of optimized shapes that maximize the propulsive efficiency, defined as the ratio of the propulsive power over the aerodynamic power, under lift, thrust, and area constraints. Several parameters affecting flight performance are investigated and their impact is described. These include the wingʼs aspect ratio, camber line, and curvature of the leading and trailing edges. This study provides guidance for shape design of engineered flying systems.
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| 34. |
- Pisculli, Andrea, et al.
(författare)
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A reaction-null/Jacobian transpose control strategy with gravity gradient compensation for on-orbit space manipulators
- 2014
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 36, s. 30-40
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics and the control of space manipulators floating in 3D space is analyzed in this paper. A minimum state variable approach for describing the dynamics of a free-floating space manipulator under gravity and gravity gradient forces is presented. A new control strategy involving a combination of Reaction Null and Jacobian Transpose controllers, including also the gravity gradient compensation, is suggested and compared with the Jacobian Transpose control and the conventional Proportional Derivative control. Several numerical examples will be presented and discussed, considering platforms with single and double manipulators, showing the advantages and drawbacks related to these control strategies.
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| 35. |
- Rizzi, Arthur, et al.
(författare)
-
Historical development and use of CFD for separated flow simulations relevant to military aircraft
- 2021
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 117, s. 106940-
-
Forskningsöversikt (refereegranskat)abstract
- Separated flows often set aerodynamic limits for an aircraft flight envelope, and many of these flows remain difficult to predict with Computational Fluid Dynamics. This paper reviews and explores how CFD simulations have been used for predicting separated flows, and the associated aerodynamic performance, throughout the flight envelope, giving special focus to NATO aircraft. The review entails: a summary of the physics of flow separation that is especially difficult to model numerically; an historical sketch of seven decades of CFD developments to meet many of the challenges of separated flow predictions; six case studies for an assessment of the current CFD capabilities; and future prospects for further improvements in the CFD simulations. Significant advances are still needed for separated flow simulations to become practical with reliabilities comparable to attached flow simulations. Some recommendations for future work are included.
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| 36. |
- Tomac, Maximilian, et al.
(författare)
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Predictions of stability and control for a flying wing
- 2014
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 39, s. 179-186
-
Tidskriftsartikel (refereegranskat)abstract
- The numerical simulation of a generic reduced radar signature tailless aircraft is considered. Investigation compares simulated data to low-speed wind tunnel experiments. Focus is on numerical predictions of steady longitudinal and lateral aerodynamics and influence of control surfaces on aerodynamic forces. Fully turbulent and transitional Reynolds Averaged Navier-Stokes (RANS) simulations predicted in agreement with experiment unstable pitch characteristics for low angles of attack (alpha), this was not the case for inviscid or laminar simulations. However, all simulations captured a sudden rapid increase in nose up pitch moment at higher angles of attack compared to experiments. Time accurate computations (URANS) captured non-linearity and unsteadiness in yaw moment with respect to differential split flap deflections for the studied angles of attack.
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| 37. |
- Zong, Lijun, et al.
(författare)
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Concurrent base-arm control of space manipulators with optimal rendezvous trajectory
- 2020
-
Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 100
-
Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a control method for space manipulators, involving concurrent operation of an optimal and a coordinated controller. The optimal controller moves center of mass of the base spacecraft to a desired position along an optimal rendezvous trajectory for minimizing the energy. The optimal control problem is solved through Calculus of Variations, using saturation functions to represent the physical limitations in thrust forces. The coordinated controller drives the arm end-effector to a desired pose (for rendezvousing with the target), as well as making the base attitude follow a desired profile. It also generates augmented reactive moments on the base spacecraft to ensure controlling its attitude when the base actuators reach their limits. Simulations of a realistic space manipulator model demonstrate the performance of the proposed concurrent control method.
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| 38. |
- Cai, Zun, et al.
(författare)
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Effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor
- 2018
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 80, s. 309-314
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports a numerical investigation on the effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor with a single rear-wall-expansion cavity. The numerical solver and the LES methods were validated against available experimental data and the numerical results were shown in good agreement with the experiments. Effect of the cavity rear wall height on the non-reacting flow fields was then investigated. It was found that the vertical flow velocity of the region located right after the expansion wave starting from the cavity leading edge was increased significantly towards the cavity when lowering the rear wall height, leading to an enhanced fuel entrainment into the cavity. Subsequently, at a larger cavity expansion ratio, the mixture inside the cavity became more fuel-rich, giving rise to a deteriorated mixing environment. In addition, the cavity recirculation zone was further compressed and the turbulent flow and scalar dissipation inside the cavity would be enhanced, which were likely the reason causing the ignition failures and poor flame stabilizations. An optimal cavity expansion ratio for the maximum fuel entrainment was found in the present rig.
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| 39. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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Wake Energy Analysis Method Applied to the Boxprop Propeller Concept
- 2018
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 79, s. 689-700
-
Tidskriftsartikel (refereegranskat)abstract
- Inspired by Prandtl's theory on aircraft wings with minimum induced drag, the authors have introduced a double-bladed propeller, the Boxprop, intended for high-speed flight. The basic idea is to join the propeller blades pairwise at the tip to decrease tip vortex strength and improve mechanical properties compared to a conventional propeller. The present work develops a wake analysis method allowing an energy breakdown of the flow as well as making the irreversibility of the flow explicit by using the entropy lost work concept. The method quantifies the strength of flow features such as tip vortices and wakes in terms of engine power. In contrast to existing work, this method removes assumptions of uniform flow, no radial flow, and constant static pressure in the propeller jet. The results of the wake analysis method can be summarized into three key findings 1) the energy in the tip-vortex of the Boxprop design is comparatively speaking non-existent, 2) the swirl energy level of the Boxprop is higher and this turbomachine is thus more in need of a downstream counter-rotating blade to recover the energy, 3) the Boxprop develops a much larger part of its thrust closer to the hub. Analysis of this aspect of the flow reveals that blade interference approaching the tip, where the blades in a pair are more closely spaced, is quite pronounced. In turn, this indicates that maximum efficiency Boxprop designs are more likely to be obtained by having larger axial separation of the two blades.
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| 40. |
- Chen, Yuqian, et al.
(författare)
-
Experimental and numerical study of flow and ignition and lean blowout characteristics of jet-cooled wall flameholder in a dual-mode combustor
- 2022
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 122
-
Tidskriftsartikel (refereegranskat)abstract
- The wall flameholder is one of the credible alternatives to realize pilot ignition in augmented/ramjet combustors. To overcome the ablation for a long-term operation, two types of jet cooling, external-inhaled air and pressure-driven jet cooling, are proposed for the wall flameholder. In this work, the flow and combustion process in a laboratory scale rig is studied for different cooling schemes and cooling conditions using experimental and numerical methods. Flow analysis in pressure-driven jet cooling scheme shows that the flow field of flameholder is influenced significantly by the cooling hole angle on the oblique plate α and on the rear plate β. In particular, the cooling jet angle combinations (α=30o, β=30o) and (α=90o, β=150o) are the two schemes with the most different characteristics. To investigate the effects of jet cooling type and cooling jet angle on the flow, ignition, and lean blowout (LBO) characteristics, the two distinctively different angle combinations are applied to form two kinds of jet cooling schemes mentioned above. Results suggest that the jet cooling type has less impact on the flow field but more influence on the flow loss than the cooling jet angle. The ignition performance of cooling schemes with α=30o and β=30o is better than that of those with α=90o and β=150o, but it has a more significant flow loss. The LBO limits of external-inhaled air cooling are lower than that of pressure-driven jet cooling. Moreover, the ignition and LBO limits decrease gradually with the increased mainstream temperature and they are only slightly affected by the mainstream velocity. Notably, the pressure-driven jet cooling scheme can slightly reduce the flow loss but it leads to a deteriorated ignition and LBO performance. The external-inhaled air cooling scheme with α=30o and β=30o has an excellent ignition and LBO performance, and the ignition and LBO limits increase with the increasing cooling air flow rate and the decreasing cooling air temperature.
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| 41. |
- Chen, Yuqian, et al.
(författare)
-
Experimental study on combustion and flow resistance characteristics of an afterburner with air-cooled bluff-body flameholder
- 2022
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 123
-
Tidskriftsartikel (refereegranskat)abstract
- In the afterburner assembled with an air-cooled bluff-body flameholder, cooling air is directly injected into the recirculation zone behind the bluff-body, which can reduce the local temperature and increase the oxygen concentration of the gas mixture in the wake of the bluff-body, thereby affecting the total pressure loss and combustion characteristics. To better understand the flow and combustion process of the system, the exhaust gas temperature, cold and hot total pressure losses in a rectangular premixed combustor are investigated under different cooling air jet conditions. Experimental results show that the added cooling air could improve the combustion efficiency and widen the blowout limit, whereas it could also give rise to an extra total pressure loss. However, when the cooling air flow rate was higher than a critical value, i.e., after the blowing ratio reached 2.5, the recirculation zone could be blown away, resulting in a failed ignition in the afterburner. Notably, the decreased temperature difference between the mainstream and the cooling air could improve the combustion efficiency and reduce the thermal resistance loss but enlarge the cold flow loss and hot total pressure loss. Moreover, since the oxygen content declined and autoignition appeared after the mainstream temperature reached 1100 K, the exhaust gas temperature and combustion efficiency declined rapidly, and the hot total pressure loss also decreased. In addition, with the fuel-gas ratio increasing, the combustion efficiency significantly dropped, the exhaust gas temperature and thermal resistance loss firstly increased to a peak value (at the equivalence ratio of 1.14) and then decreased for excessively fuel-rich combustion.
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| 42. |
- Chen, Youqian, et al.
(författare)
-
Influences of accelerating states on supercritical n-decane heat transfer in a horizontal tube applied for scramjet engine cooling
- 2021
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 109
-
Tidskriftsartikel (refereegranskat)abstract
- Supercritical n-decane is applied in the regenerative cooling system of scramjet engines while scramjets are always in various irregular movements. With the desire to explore heat transfer performance of supercritical n-decane under actual flight conditions, numerical simulations and analysis of different states during the accelerated flight process are carried out under three different heat fluxes and eight varying acceleration states. Specific flow and heat transfer mechanisms are explored by analyzing the temperature and flow fields affected by acceleration. Results show that acceleration weakens the intensity of the first abnormal heat transfer state but does not affect its appearance location, and there are almost no effects on the second heat transfer state. Another important conclusion is that the external factors have a great influence on supercritical n-decane heat transfer. The overall average surface heat transfer coefficient could be even up to 27.5% higher than for an ordinary horizontal tube. It is indicated that more attention should be paid to the external factors when investigating supercritical flow and heat transfer in the research and development of scramjet engine cooling.
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| 43. |
- Chen, Yuqian, et al.
(författare)
-
Investigation of flame characteristics and cooling effectiveness of jet-cooled wall flameholders in vitiated flow
- 2022
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 127
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental and numerical studies were performed to understand the flame characteristics and cooling effect of jet-cooled wall flameholders in a simplified augmented combustor. The time-averaged flame structure and wall temperature were investigated employing an instantaneous flame capturing system with image processing technology and a wall temperature measurement system, respectively. Flow and fuel distribution simulations were carried out to analyze the flame structure and cooling effect of the jet-cooled flameholders in high-temperature and high-velocity vitiated flows. It was found that the jet cooling type and the cooling jet angle on the oblique plate α and on the rear plate β greatly affect the flame features and cooling effect of the flameholder. The external-inhaled air cooling schemes can increase the flame luminosity and temperature and create a flame hollowed-out zone in the near-wall region to reduce flame radiation and heat convection, thereby achieving an excellent cooling effect. The pressure-driven gas jet cooling schemes yielded a weaker flame luminosity and its flame structure in the cavity more sensitive to the cooling jet angle than external-inhaled air cooling schemes. Moreover, the external-inhaled air cooling schemes have significantly better cooling effects than the pressure-driven gas jet cooling schemes under different mainstream conditions and fuel flow rates. Notably, the cooling schemes with α=30∘ and β=30∘ have more uniform wall temperature than that of α=90∘ and β=150∘ on the above two plates. Furthermore, the external-inhaled air cooling scheme with α=90∘ and β=150∘ has the best cooling performance under different mainstream and cooling air conditions and presents great cooling effectiveness in the case of enhancing cooling air temperature.
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| 44. |
- Chen, Yuqian, et al.
(författare)
-
Study on ignition process and flame expansion and propagation characteristics in jet-cooled pilot flameholders using image processing techniques
- 2022
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 129
-
Tidskriftsartikel (refereegranskat)abstract
- Wall-type pilot flameholder has been used in aero-engines to effectively create a stable ignition source and achieve an excellent ignition performance in high-velocity flows. The ignition delay, flame propagation, and flame boundary are crucial characteristics to evaluate the performance of pilot flameholders. Previous work displayed the significantly changed ignition performance and flow features of the wall flameholder when jet cooling schemes were adopted, indicating that the ignition process and the flame features strongly depend on the cooling jet and the optimal design of jet cooling schemes needs further investigation. Therefore, in this study, two practical image processing algorithms are developed to characterize the flame development of the ignition process, reveal the effect of cooling schemes on the ignition delay time, and quantitatively analyze the flame area and expansion ratio of the wall flameholder during stable combustion. Two image processing methods proposed based on MATLAB algorithms exhibit effectiveness in studying the ignition process and flame expansion characteristics. The ignition process is divided into four phases: kernel generation, kernel propagation, flame growth, and stable combustion. Meanwhile, the ignition delay time is identified by counting the total pixels of the flame projected region during the ignition process. The edge detection and pixel statistics of the flame projected region in the binary luminosity image show the flame boundary and expansion ratio under various working conditions. It was found that the cooling jet angle has a significant impact on the ignition process, ignition delay time, flame propagation, and steady flame features. The pressure-driven gas jet cooling scheme with a smaller jet angle and the external-inhaled air cooling scheme with a larger jet angle present a better capability of ignition and flame expansion and propagation.
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| 45. |
|
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| 46. |
- Fureby, Christer, et al.
(författare)
-
Large Eddy Simulation of cavity stabilized ramjet combustion
- 2023
-
Ingår i: Aerospace Science and Technology. - 1270-9638. ; 141
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we use finite rate chemistry Large Eddy Simulation (LES) to examine flow, injection, mixing, self-ignition and turbulent combustion in a dual-mode ramjet combustor with a cavity flameholder. The target case is the dual-mode ramjet combustor studied experimentally by Micka & Driscoll in a series of publications under different operating conditions characterized by varying air stagnation temperatures, T0, and fueled with hydrogen or hydrogen-ethylene blends. Here, only hydrogen fuel is considered. Three skeletal and comprehensive chemical reaction mechanisms are used to evaluate the influence of the reaction mechanism. Based on comparisons with ignition, laminar flame, and dual-mode ramjet combustor experiments the Z22 mechanism is found superior to the D7 and J20 mechanisms, which is then used throughout this study. For the ramjet experiments, two stabilization modes were reported: cavity-stabilized combustion at low T0 and jet-wake-stabilized combustion at high T0. For in-between values of T0, combustion oscillates between these modes. The LES results using the Z22 reaction mechanism are in good agreement with the experimental data: cavity-stabilized combustion is observed for low T0, and for this case combustion anchors at the leading-edge of the cavity. For high T0 jet-wake-stabilized combustion occurs in the near-wake of the fuel-plume. Between these two modes, combustion oscillates between modes that can be roughly identified as jet-wake and cavity stabilized. The LES predictions also reveal details about high-frequency oscillations (∼1 kHz) that are observed in particular for low and intermediate T0. The H2-air mixture appears to burn as an auto-ignition assisted premixed flame in the cavity-stabilized case, and as a diffusion-flame in the jet-wake stabilized case, whereas for the in-between cases, the burning modes changes accordingly.
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| 47. |
- Grosshans, Holger, et al.
(författare)
-
Modeling the electrostatic charging of a helicopter during hovering in dusty atmosphere
- 2017
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 64, s. 31-38
-
Tidskriftsartikel (refereegranskat)abstract
- A helicopter flying through an atmosphere containing particulates may accumulate high electrostatic charges which can challenge its operational safety. In this paper we elaborate and validate a triboelectric charging model to predict the electrification experienced by a helicopter while hovering in dusty air. We employed Large Eddy simulations to describe the turbulent structures inherent in the flow around the rotorcraft. The dust particles were tracked individually in a Lagrangian framework. A model accounting for the triboelectric charge transfer when a particle hits the helicopter was introduced. The results demonstrate the accuracy of the proposed approach and allow a detailed analysis of the location of the charge accumulation.
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| 48. |
- Huang, Zhongjie, 1985, et al.
(författare)
-
Aeroacoustic analysis of aerodynamically optimized joined-blade propeller for future electric aircraft at cruise and take-off
- 2020
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 107
-
Tidskriftsartikel (refereegranskat)abstract
- A novel propeller with the blade tips joined in pairs, named Boxprop, is designed and optimized for a conceptual electric aircraft using an efficient optimization platform. According to the thrust requirement of the electric aircraft at cruise, the Boxprop with optimal efficiency is down-selected from the Pareto front of thrust coefficient and propeller efficiency. Furthermore, the blade pitch angle is adjusted to meet the thrust requirement at take-off. It is found that the Boxprop is capable of suppressing tip vortices and inducing a wider wake behind blade tip in comparison to a conventional propeller usually shedding a concentrated tip vortex, which could potentially improve the propulsive efficiency. Afterwards, the aeroacoustic analysis performed by the hybrid integral method of Reynolds-Averaged Navier Stokes equations (RANS) and convected Ffowcs Williams and Hawkings (FW-H) equation shows that the tonal noise from the Boxprop with three joined blades operating at cruise is similar to a conventional three-bladed propeller, though being stronger than a conventional six-bladed propeller. Although the tip vortices have been suppressed by the joined-blade tips of the Boxprop, the corresponding tonal noise reduction is not prominent. Next, the Boxprop noise at take-off is studied. Unsteady RANS is used to resolve varying flow structures that become dominant under the take-off condition. Angle of attack (AOA) is found as an important factor influencing the noise generation. The radiated noise upstream and downstream of the propeller significantly intensifies due to increasing AOA. The AOA effects of the Boxprop follow a similar trend to a conventional propeller. The findings for the Boxprop aeroacoustics have enhanced the understanding of tip-vortex suppression techniques in connection with the tonal noise generation, which will be greatly helpful to the aeroacoustic design of Boxprop applied to electric aircraft in the future.
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| 49. |
- Li, Peibo, et al.
(författare)
-
Three-dimensional flow structures and droplet-gas mixing process of a liquid jet in supersonic crossflow
- 2019
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 90, s. 140-156
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Tidskriftsartikel (refereegranskat)abstract
- The mixing process of a liquid jet in supersonic crossflow with a Mach number of 2.1 was investigated numerically using large eddy simulation (LES) based on the Eulerian-Lagrangian method. The gas phase was described using the Navier-Stokes equations and the liquid phase was represented using discrete droplets, which were injected and tracked in the computational domain individually according to Newton's second law of motion. The KH (Kelvin-Helmholtz) breakup model was used to calculate the droplet stripping process, and the secondary breakup process was simulated by coupling the RT (Rayleigh-Taylor) breakup model and the TAB (Taylor Analogy Breakup) model. Two-way coupling was enforced to consider the momentum and energy exchange between the gas and the droplets. It was found that the LES predicted spray characteristics, including spray penetration and cross-sectional distribution, agree reasonably well with the experiment. The major gas flow structures such as the bow shock, the large-scale vortices, and the recirculation zones were replicated successfully in the simulations. It was found that the gas flow structures have a significant effect on the mixing process of the droplets. The simulation results revealed that two sets of counter-rotating vortex pair (CVP) exist in the gas-liquid mixing region. Under the influence of CVP, part droplets were transported to the near wall region and subsequently to both sides of the core spray region. The formation mechanism of the CVP was analyzed by comparing the pressure gradient and the source term of droplets in the Navier-Stokes equations. Differences of the mixing process of liquid jet in supersonic crossflow, gas jet in supersonic crossflow and liquid jet in incompressible crossflow were identified.
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- Li, Shuai, 1990, et al.
(författare)
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On the mitigation of landing gear noise using a solid fairing and a dense wire mesh
- 2024
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Ingår i: Aerospace Science and Technology. - 1270-9638.
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Tidskriftsartikel (refereegranskat)abstract
- A solid fairing and a wire-mesh fairing consisting of very fine wires and pores are numerically and experimentally investigated for the mitigation of landing gear noise. A slightly modified LAGOON landing gear and two configurations, one equipped with a solid fairing and the other with a wire-mesh fairing, are numerically simulated using the Improved Delayed Detached-Eddy Simulation (IDDES) in combination with the Ffowcs Williams and Hawkings (FW-H) analogy. Instead of resolving the detailed flow features through the wire mesh, a recently proposed numerical model is used to represent the effect of the wire-mesh fairing. The simulated flow fields and the far-field noise spectra are validated against the experiments conducted in an anechoic wind tunnel. The superiority of the recently proposed wire-mesh model over a classical wire-mesh model in modeling both the aerodynamic and aeroacoustic effects of the wire mesh is demonstrated. Results also show that the dense wire-mesh fairing functions very similarly to the solid fairing and that significant noise can be reduced through the installation of a solid fairing or a wire-mesh fairing upstream of the landing gears. For the baseline landing gear, the torque link and the brakes are identified noise sources. With the aerodynamic penalty of a 50% increase in drag, both fairings mitigate the pressure fluctuation on the torque link and brakes, resulting in the reduction of surface noise sources. The noise directivity shows that a solid fairing or a dense wire-mesh fairing contributes to a noise reduction of 4-6 dB in all radial directions. The findings in this study pave the way for the low-noise design of aircraft landing gears.
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