| 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
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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
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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
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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. |
- Cai, Zun, et al.
(författare)
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Effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor
- 2018
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 80, s. 309-314
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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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