| 1. |
- Cuppoletti, Dan, et al.
(författare)
-
A Comprehensive Investigation of Pulsed Fluidic Injection for Active Control of Supersonic Jet Noise
- 2013
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Ingår i: 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. - Reston, Virigina : American Institute of Aeronautics and Astronautics. ; 2013
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Konferensbidrag (refereegranskat)abstract
- Fluidic injection for noise control of high Reynolds number jets has shown promise and recent tests have demonstrated improved noise reduction while decreasing the injection mass flow required. This investigation was an experimental and numerical study on the capability of pulsed fluidic injection to reduce noise on a Md = 1.56 supersonic jet. The effect of pulse frequency, duty cycle, injector phasing, and injection angle on the noise components were studied. The pulsed injectors were characterized with hot-wire measurements. Far-fleld acoustics was used to survey the noise reduction of pulsed injection (up to 400 Hz) in comparison to the baseline and steady injection cases. Injection angles θinj = 30° to 90° with respect to the primary jet axis were investigated. High-speed shadowgraph was used to quantify the time scales involved in response of the shock train and screech instabilities with pulsed fluidic injection. LES and CAA were compared with measurements to evaluate the capability of numerical simulation of the pulsed injection configurations. It was shown that reduction of turbulent mixing noise generally scales with the actual duty cycle of applied injection. For 30 Hz injection at 20% mass flow up to up to 80% of the steady flow {increment}OASPL is achieved, demonstrating that low frequency injection is capable of enhanced noise reduction at certain conditions. The shocks in the jet potential core respond in 1 ms when injection is removed, while the jet column instability requires up to 7 ms to redevelop after injection is removed. The results demonstrate the feasibility of using active control with pulsed fluidic actuators to provide at least steady flow noise reduction with significantly reduced injection mass flow.
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| 2. |
- Cuppoletti, Daniel, et al.
(författare)
-
Analysis of Supersonic Jet Thrust with Fluidic Injection
- 2014
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Ingår i: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014; National Harbor, MD; United States; 13 January 2014 through 17 January 2014. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102561
-
Konferensbidrag (refereegranskat)abstract
- Considerable focus on noise abatement for aircraft has spawned various noise control devices, passive and active. Aircraft and propulsion system design now has the additional criteria of acoustic performance to consider among many other criteria in advanced flight vehicle design. It is essential to consider the effect that noise control methods have on the performance of the propulsion device and overall effect on system performance. Thrust calculated from measurements and LES are compared for a Md = 1.56 jet at various operating conditions for validation. Experimental measurements on the baseline supersonic jet are used to validate computational results for the pressure and momentum thrust components. Thrust for various fluidic injection configurations are evaluated using computational results from the highly three dimensional flowfield. Analysis and discussion of requirements for fluidic injection air are provided to develop a complete system approach to aid design of fluidic injection systems. Fluidic injection decreases momentum thrust by creating axial velocity deficits in the region of injection. Pressure thrust is increased from local pressure rise from the injectors and area control at the nozzle exit. Fluidic injection increases total thrust as the pressure thrust gains are greater than the momentum thrust deficits. Specific thrust is reduced slightly with 6 injectors being a more efficient use of the injection air with greater noise reduction.
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| 3. |
- Cuppoletti, Daniel, et al.
(författare)
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Elimination of shock associated noise in supersonic jets by destructive wave interference
- 2018
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Ingår i: AIAA Aerospace Sciences Meeting, 2018. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied resulting in unique acoustic behavior and flow field modifications. For most conditions the acoustics are relatively unaffected or increased, but for very specific conditions noise was drastically decreased. For optimized conditions the shock noise was completely eliminated and in other cases a jet instability was generated that significantly decreased high frequency noise. Measurements of the velocity field indicated that shock interaction due to shocks from the injection jet interact with the primary jet shocks, and significantly reduce the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with LES, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of OASPL of -7 dB at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction, destructive interference of the shock structure in the jet is reported.
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| 4. |
- Cuppoletti, Daniel, et al.
(författare)
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Elimination of Shock-Associated Noise in Supersonic Jets by Destructive Wave Interference
- 2019
-
Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 57:2, s. 720-734
-
Tidskriftsartikel (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied, resulting in unique acoustic behavior and flowfield modifications. For most conditions, the acoustics are relatively unaffected or increased, but for very specific conditions, noise was drastically decreased. For optimized conditions, the shock noise was completely eliminated, and in other cases, a jet instability was generated that significantly decreased high-frequency noise. Measurements of the velocity field indicated that shock interaction, due to shocks from the injection jets, interacts with the primary jet shocks and significantly reduces the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with large-eddy simulation, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of overall sound pressure level of -7 d B at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction and destructive interference of the shock structure in the jet is reported.
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| 5. |
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| 6. |
- Cuppoletti, Daniel, et al.
(författare)
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The Role of Nozzle Contour on Supersonic Jet Thrust and Acoustics
- 2014
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Ingår i: AIAA Journal. - : American Institute of Aeronautics and Astronautics (AIAA). - 1533-385X .- 0001-1452. ; 52:11, s. 2594-2614
-
Tidskriftsartikel (refereegranskat)abstract
- This work is an experimental and computational investigation of acoustics and performance of a biconical and splined supersonic nozzle to identify the dependencies of noise components on the nozzle design. The convergent section and throat of a biconical supersonic nozzle were optimized with a Reynolds-averaged Navier-Stokes solver to optimize thrust and minimize internal losses. Far-field acoustics and the jet flowfield were measured and studied using large-eddy simulations at design, overexpanded, and underexpanded conditions. The biconical and splined nozzles are designed to be thrust matched at fully expanded conditions. The convergent section and throat contour do not significantly affect the turbulent mixing noise or shock-associated noise at most conditions. Analysis of the jet flowfield shows differences in shock structure, although the "global" shock strength remains relatively unchanged. A comparison of measurements and computations of mean velocity and turbulence shows minor differences in the shear-layer region and near strong shocks. Momentum thrust and pressure thrust were measured and compared with computational results. The contoured throat nozzle provides equivalent thrust with a 4% lower nozzle pressure ratio at the design condition with no acoustic penalty. At equivalent nozzle pressure ratios, the contoured nozzle provides 10% higher thrust with no increase in mixing noise or shock noise.
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| 7. |
- Daniel, Cuppoletti, et al.
(författare)
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Nozzle Throat Optimization on Acoustics and Performance of a Supersonic Jet
- 2012
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Ingår i: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference). - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- Nozzles used in supersonic flight applications have flow contours that cause the flow to differ from isentropic nozzle flow, resulting in less than ideal nozzle performance. The impact of nozzle contour on performance is well quantified, however it is less clear how the nozzle contour affects supersonic jet noise. This work investigates differences in noise characteristics of a sharp throat and contoured throat nozzle to identify the dependencies of supersonic noise components on the nozzle design. The nozzles are designed to be thrust matched at fully expanded conditions. The throat contour does not significantly affect the acoustics at fully expanded conditions, although the nozzle efficiency is increased for the contoured throat nozzle. Contouring the throat causes the nozzle to have screech instabilities over a broader range of operating conditions when imperfectly expanded. A detailed PIV and LES investigation was used to explain the acoustics behavior at all conditions. Reducing the throat shock strength increased the nozzle exit shock strength and periodicity, subsequently increasing the susceptibility to screech. Nozzle performance is increased at all operating conditions with the contoured throat nozzle.
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| 8. |
- Gustafsson, Bernhard, 1971, et al.
(författare)
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Nozzle throat optimization for supersonic jet noise reduction
- 2012
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Ingår i: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition 2012. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- Noise from engines that operate at supersonic conditions, especially high performance military aircraft, often utilize a converging-diverging nozzle with variable area control. This design usually includes a sharp nozzle throat which creates internal shock formation. Turbulent structure interaction with these shocks results in additional noise components other than turbulent mixing noise to be introduced to the jet noise spectrum. The present study investigates how weakening the internal shocks affects the flow and acoustics of a Mach 1.6 jet. RANS simulations were used to minimize internal shock formation and optimize the flow contours of the converging portion and throat of a C-D nozzle. A response surface methodology was used to evaluate 3000 possible designs using the RANS results as model inputs. An experimental investigation was conducted with a splined nozzle design that is virtually free of internal shocks. The flow field was measured using PIV for comparison with RANS and LES. Mean velocity and turbulence was captured well by the computations for the sharp throat and splined nozzles. Although the throat shocks were nearly eliminated, the overall shock strength was relatively unchanged. Far-field acoustic results showed little difference at thrust matched conditions since the overall shock strength was unchanged. The nozzle performance is greatly improved through throat optimization, providing equivalent thrust with 4% less pressure with no acoustic penalty.
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| 9. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Acoustic Signature of a Supersonic Jet Emanating from a Rectangular C-D Nozzle
- 2016
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Ingår i: 54th AIAA Aerospace Sciences Meeting, 2016, San Diego, United States, 4-8 January 2016. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624103933 ; 0
-
Konferensbidrag (refereegranskat)abstract
- We live in a world with ever increasing air traffic and the demand for fuel efficient low noise emitting aircraft is high. The use of blended wing bodies (BWB) has gained interests within the aerospace industry due to its potential for reduced fuel consumption. These type of aircraft are generally equipped with rectangular nozzles. The drawback of such nozzles is increased instability of the emanating jet which increases the risk of higher noise radiation. Understanding the instability patterns and the underlying flow physics is therefore the key to improved stability and reduced noise. In the presented paper, an LES/CAA approach is utilized to predict the flow dynamics and the radiated noise from a rectangular nozzle. The nozzle is operated at underexpanded conditions. The simulations are compared with experiments and are used as a complement to the experimental data for improved understanding of the flow physics. The supersonic jet is found to exhibit an intense flapping motion followed by a large jet spreading in the minor-axis plane. In general, the prediction of the most amplified frequency and higher harmonics observed in the near-field and far-field spectra is in agreement with the experiment. Two types of flow events associated with the generation of high amplitude acoustic waves are detected. These events are identified as vortex-collision and shock-leakage through the shear layer.
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| 10. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Active Suppression of Supersonic Jet Noise Using Pulsating Micro-Jets
- 2012
-
Ingår i: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Nashville, 9-12 January 2012. - Reston, Virigina : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- Noise suppression devices on military jet engines are motivated by the need to reduce community noise aswell as the acoustic load on airfield personnel during peacetime operation. They may also reduce problemswith sonic fatigue on the aircraft. Micro-jets have previously been shown as a promising tool for active noisesuppression. In the work presented here, compressible LES simulations have been done for slightly overexpandedconical C-D nozzle with a Mach number of 1.58 at NPR = 4.0 and a free stream flow Mach numberof 0.1. Two microjet configurations have been simulated. One with steady-state injection and an other withpulsating trailing-edge injection having a maximum mass flow-rate of mi/mj = 1.6%. The acoustic field isexpanded to the far field using the Kirchhoff integral method. The effect of injection frequency and pulsationcharacteristics on the flow-field and the radiated sound is investigated. Comparison is made between the LESand simulations and experiments for the steady-state and no injection cases and shows excellent agreement forthe screech tone frequency and the predictided OASPL is within 2 dB deviation from the measurements. Thepulsating injection cases investigated show that the frequency spectrum and the noise levels are sensitive to theinjection frequency as well as pulsation characteristics. It is shown that steady-state injection and pulsating injectionof equal max mass flow result in comparable reduction in terms of OASPL. The latter, however, comeswith the penalty of increased noise for the upstream observers.
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| 11. |
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| 12. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Exploration of temperature effects on the far-field acoustic radiation from a supersonic jet
- 2014
-
Ingår i: 20th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102851
-
Konferensbidrag (refereegranskat)abstract
- Jet engines designed for high-speed aircraft commonly include C-D nozzles to obtain supersonic speeds. The radiated noise from the jet exhaust reaches acoustic levels which may cause hearing damage to the pilot and the air-field personnel even though state of the art noise protection such as noise-canceling ear muffs are employed. It is therefore extremely important to keep the noise levels as low as possible. Understanding the noise generation mechanism is of great importance in order to reduce strength of the noise sources. Typical far-field noise spectral characteristics from the supersonic jet exhaust consist of turbulent mixing noise and shock-associated noise. Another noise component named'crackle' is radiated from the jet under certain circumstances. Although it does not appear in the noise spectra due to its characteristics, its rasping character is perceived as a dominant annoyance factor by the human ear. Since it does not appear in the spectrum other measures are needed to identify the existence of'crackle'. Statistical tools like Skewness and Kurtosis applied to the far- and near-field pressure signals and the time derivate of the pressure signal have been shown in literature to be useful for identification of'crackle' events. In this paper the near-field and far-field acoustic radiation from a supersonic jet is analyzed using LES with a code developed at Chalmers University of Technology. The code has previously shown to accurately capture far-field noise spectra of supersonic jets under a variety of moderately cool jet conditions. In the present study we move towards more realistic high-speed aircraft conditions with higher jet exhaust temperatures. The nozzle is operated at slightly underexpanded conditions (NPR = 4.0) and three different stagnation temperature ratios NTR = 1.0, NTR = 2.0 and NTR = 3.0. The LES results are compared with experiments conducted at the Gas Dynamics and Propulsion Laboratory at the University of Cincinnati.
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| 13. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Near-field and far-field spectral analyzis of supersonic jet with and without fluidic injection
- 2014
-
Ingår i: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014; National Harbor, MD; United States; 13 January 2014 through 17 January 2014. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102561
-
Konferensbidrag (refereegranskat)abstract
- In the presented study the time-dependent flow features of a supersonic jet with and without steady microjet injection are investigated. The flow field is sampled at various axial and radial locations in the supersonic region and its near surroundings. The jet is emitted from a sharp-throat converging diverging nozzle operated at a nozzle pressure ratio (NPR) of 4.0, which gives a jet exitMach number of M = 1.56 and a Reynolds number of Re = 2.46×106 based on the jet exit diameter. Large Eddy Simulation (LES) is used to obtain the fully three dimensional instantenous turbulent flow field and the Kirchhoff surface integral method is applied to obtain the far-field radiated noise. Both the near-field flow dynamics and the far-field noise obtained from the LES are in good agreement with experimental data. The noise components in the far-field noise are identified and compared with the spectra obtained from the probe-locations within the jet. The effect of micro-jet injection on the spectral characteristics within the jet and the far-field noise is analyzed. The screech tone appearing in the far-field noise is clearly established also in the jet-plume. Two point cross-correlations within and outside the supersonic region of the jet-plume revealed two types of moving phenomenon. These where found to be turbulent structures and acoustic waves. The odd thing at first sight was that the acoustic waves appeared to be traveling upstream within the supersonic region, which sounds contradictory. However, it was showed that the acoustic wave was traveling in the form of a helical mode which allows the phase velocity of the pressure wave to be higher than the flow velocity, even at supersonic flow speeds. The fluidic injection was shown to disrupt and weaken the helical pattern which resulted in a lower far-field screech tone noise. Upon sufficient dissipation of the injection, a few nozzle diameters downstream of the nozzle exit, the helical pattern picks up strength again. However, the feed-back loop mechanism associated with the screech tone is still disabled.
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| 14. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
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Noise Control of Supersonic Jet with Steady and Flapping Fluidic Injection
- 2015
-
Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 53:11, s. 3251-3272
-
Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulation is used to investigate steady-state mass flow injection into a supersonic jet stream with and without flapping motion of the microjets. The results are validated with particle image velocimetry and acoustic measurements. The effect of microjet penetration on the far-field acoustics is studied by altering the number of injectors, the cross-sectional area of each injector, and the injection mass flow. The injectors are evenly distributed around the nozzle exit. The injection angle is 90 deg relative to the main jet flow. This research is a continuation of a previous large-eddy simulation study of pulsed injection that showed that the unsteady injection-induced pressure pulses in the jet caused increased tonal noise for far-field observers at low angles. Flapping jet injection was shown to minimize the creation of the pressure pulses, except for high-amplitude flapping angles and high injection mass flows, where the injections divert out of the shear layer and introduce periodic superposition of the double shock-cell structure. Furthermore, the flapping injection did not show improved noise reduction compared with the steady injection, which is essentially promising because steady injection proves to be a more practical solution for implementation in real jet engine applications.
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| 15. |
- Hafsteinsson, Haukur, 1984
(författare)
-
Numerical Simulations of Noise Reduction Devices for Aero Engines
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing air traffic and denser population around airports have led to stricterregulations on aircraft noise. The engine is the main source of noise of jet aircraft.Decreasing jet engine noise can in some cases reduce sonic fatigue andthereby increase the engine lifetime. In this thesis the performance of a novellow-frequency acoustic liner concept is investigated using unsteady Reynolds-Averaged Navier-Stokes simulations (URANS). The results are compared withthose of an analytical model and experiments. The liner is designed to reduce fannoise upon placement on the outlet guide vanes. Furthermore, the response of theradiated noise from a supersonic jet emitted from a converging diverging nozzleto steady-state and pulsed fluidic injection is tested using Large Eddy Simulation(LES). An investigation is also presented in which actions were taken to reducethe internal shock strength by modifying the nozzle throat, and thereby reduce theresulting noise. The optimized nozzle was evaluated further using LES and experimentaltechniques. The acoustic liner study showed that the resonance frequencyof the liner obtained by the URANS compared within 200Hz to the measuredresonance frequency. It was shown that the analytical model can be tuned with asingle parameter to match the URANS simulations over a wide range of frequencies.Simulations of the sharp throat CD-nozzle with and without fluidic injectioncompared within 2 dB to the measured values of the overall sound pressure level(OASPL) for all observers. The pulsed injection showed that the radiated noiseis sensitive to the pulsation characteristics and the frequency. It was shown thatnoise reduction with pulsed injection can equal the noise reduction of steady-stateinjection with lower net mass flow of the pulsed injection. However, an increasednoise was noted at the downstream observers. The optimized nozzle nearly eliminatesthe internal shock, which reduces the double diamond structure in the jetplume but increases the strength of the shock at the nozzle exit. It has lower turbulencelevels at the nozzle exit due to a weaker shock interaction with the shearlayer. The optimized nozzle provides equal thrust to the sharp nozzle with 4%lesspressure without any acoustic penalty. Good comparison is obtained with RANS,LES and experiments.
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| 16. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Reduction of supersonic jet noise using micro-jets in the diverging part of a conical CD-nozzle
- 2015
-
Ingår i: The International Conference on Jets, Wakes and Separated Flows (ICJWSF2015), June 16-18, 2015, Stockholm, Sweden.
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Konferensbidrag (refereegranskat)abstract
- Reducing the radiated noise from supersonic jets with maintainedthrust is a major challenge. An LES/CAA method and experiments are uti-lized to investigate the flow field and the far-field acoustics of a supersonic jetemitted from a circular CD-nozzle with a sharp throat. Air is injected into thedivergent section of the nozzle using 12 evenly distributed micro-jets aroundthe nozzle circumference and the change in total thrust and acoustic signa-ture is investigated. The micro-jets are shown to decrease shock-strength withincreased injection until an optimum point where further increase in injectionmass flow caused increased shock-strength. As a consequence of the reducedshock strength, the far-field shock-noise was decreased. The net thrust wasshown to increase with increased injection mass flow, whereas the specificthrust was slightly decreased. Micro-jet injection into the divergent sectionof a CD-nozzle appears, therefore, to be an effective configuration for reducedshock-noise radiation from supersonic jets.
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| 17. |
- Hafsteinsson, Haukur, 1984
(författare)
-
Study of Supersonic Jet Noise Reduction using LES
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increases in air traffic and denser population around airports have led to stricterregulations on aircraft noise. High noise levels from high-speed aircraft can causehearing damage in pilots and the airfield personnel. The engine is the main sourceof noise of all jet aircraft and is therefore a key component for improvement.Decreasing jet engine noise can in some cases reduce sonic fatigue and therebyincrease the engine lifetime. In this thesis, the response of the radiated noise froma supersonic jet emitted from a converging diverging nozzle to steady-state, pulsedand flapping fluidic injection is studied using Large Eddy Simulation (LES), andcomparisons are made with experimental data. An investigation is also presentedin which actions were taken to reduce the internal shock strength by modifying thenozzle throat, and thereby reduce the radiated noise. The optimized nozzle nearlyeliminates the internal shock, which reduces the double diamond structure in thejet plume but increases the strength of the shock at the nozzle exit. It has lowerturbulence levels at the nozzle exit due to a weaker shock interaction with theshear layer. The optimized nozzle provides equal thrust to the sharp nozzle with4 % less pressure without any acoustic penalty. The pulsed injection showed thatthe radiated noise is sensitive to the pulsation characteristics and the pulsation fre-quency. It was shown that the noise reduction with pulsed injection can equal thenoise reduction of steady-state injection with a lower net mass flow of the pulsedinjection. However, increased noise was noted at the downstream observers. Theflapping injection cases that were investigated did not show improvements overthe corresponding steady injection cases. These are positive findings, since steadyinjection should be simpler and more robust to apply to real jet engines. Theinjection was shown to impact the jet thrust, as expected. The net jet thrust in-creased with increased injection mass flow, whereas the specific thrust decreased.The momentum thrust was shown to decrease with increased injection mass flowwhereas the pressure thrust increased due to a shock shift at the nozzle exit. Thework presented in this thesis adds to the body of knowledge found in the liter-ature about supersonic jet noise generation and its noise reduction using fluidicinjection.
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| 18. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
-
Supersonic Jet Excitation using Flapping Injection
- 2013
-
Ingår i: American Physical Society, Division of Fluid Dynamics 66th Annual Meeting, November 24–26, 2013 Pittsburgh, Pennsylvania.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Supersonic jet noise reduction is important for high speed military aircraft. Lower acoustic levels would reduce structural fatigue leading to longer lifetime of the jet aircraft. It is not solely structural aspects which are of importance, health issues of the pilot and the airfield personnel are also very important, as high acoustic levels may result in severe hearing damage. It remains a major challenge to reduce the overall noise levels of the aircraft, where the supersonic exhaust is the main noise source for near ground operation. Fluidic injection into the supersonic jet at the nozzle exhaust has been shown as a promising method for noise reduction. It has been shown to speed up the mixing process of the main jet, hence reducing the kinetic energy level of the jet and the power of the total acoustic radiation. Furthermore, the interaction mechanism between the fluidic injection and the shock structure in the jet exhaust plays a crucial role in the total noise radia- tion. In this study, LES is used to investigate the change in flow structures of a supersonic (M=1.56) jet from a converging-diverging nozzle. Six fluidic actuators, evenly distributed around the nozzle exit, inject air in a radial direction towards the main flow axis with a total mass flow ratio of 3%. Steady injection is compared with flapping injection. With flapping injection turned on, the injection angle of each injector is varied sinusoidally in the nozzle exit plane and the variation is the same for all injectors. This fluid dynamics video is submitted to the APS DFD Gallery of Fluid Motion 2013 at the 66 the Annual Meeting of the American Physical Society, Division of Fluid Dynamics (24-26 November, Pittsburgh, PA, USA).
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| 19. |
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| 20. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Aerodynamic Shape Optimization of High-Speed Trains
- 2012
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Ingår i: Civil-Comp Proceedings. - Stirlingshire, UK : Civil-Comp Press. - 1759-3433. ; 98
-
Tidskriftsartikel (refereegranskat)abstract
- The paper presents a new, fully automatic multi-objective shape optimization method for improving the aerodynamic properties of trains. The optimization method was applied to a multi-objective optimization problem of crosswind stability of a train placed on an embankment. The train was optimized with two objective functions and the geometry was changed according to two design parameters. Furthermore, two flow scenarios were used in the optimization where the train was placed either on the windward or the leeward side of the two-track embankment. The optimization resulted in an optimal shape of the train which was the same regardless of the train's location on the embankment. The present approach is shown to be robust and capable of obtaining an optimal design of the train without the influence of the user during the optimization process. The example of the optimization problem presented in this paper was multi-objective but one objective was chosen to be the dominant one. Although there are no limitations in the number of design parameters or objective functions in the method developed, an increase in the number of parameters will result in an increase in the computational effort required for the optimization. An interesting result of the present work is that almost identical optimal shapes for the train were obtained for both trains traveling on the windward and the leeward sides of the embankment. This is a desirable outcome of the optimization as it does not require selecting the shape that is optimal for only one operational condition of the train.
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| 21. |
- Larusson, Ragnar, 1986, et al.
(författare)
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Investigation of Screech in Supersonic Jets Using Modal Decomposition
- 2014
-
Ingår i: Proceedings of NSCM-27: the 27th Nordic Seminar on Computational Mechanics. - 0348-467X. ; , s. 25-28
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present study attempts to identify the eigenmodes that are associated with the screech mechanism by means of Dynamic Mode Decomposition (DMD) and a method based on the Arnoldi eigenvalue algorithm, respectively.
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| 22. |
- Larusson, Ragnar, 1986, et al.
(författare)
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Investigation of supersonic jet flow using modal decomposition
- 2014
-
Ingår i: 20th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102851
-
Konferensbidrag (refereegranskat)abstract
- Supersonic jet noise has been an important research topic for decades, both for its relevance within the aeronautical industry and for its scientific value. In the present study, the jet flow field produced by a slightly over expanded conical convergent-divergent nozzle was studied using modal decomposition. The nozzle exit Mach number is 1.58 at a nozzle pressure ratio of 4.0. The nozzle has an engine like geometry with a relatively sharp throat, creating an internal shock wave. Two different methods for modal decomposition were applied to the supersonic jet flow, namely Dynamic Mode Decomposition (DMD) and a method based on the Arnoldi algorithm. The DMD algorithm returns the eigenmodes of an approximate linear flow operator, which is constructed from the data set used in the algorithm. In the present study, the DMD algorithm was applied to observational data from a Large Eddy Simulation (LES) and 2D axisymmetric URANS simulation, respectively. The Arnoldi algorithm uses a 2D linearized flow solver to project the linear flow dynamics onto a reduced order Krylov subspace and computes the eigenmodes of that projection. Here, A steady state RANS solution of the jet flow was used as a reference state in the linear solver. The Results of the Arnoldi analysis for a azimuthal wavenumber m = 0 were directly compered with the DMD modes of a URANS simulations. It was found that both methods produce nearly identical modes in this case. The DMD modes of the LES data are comparable with the Arnoldi and URANS DMD modes in terms of frequency, acoustic radiation, and shock-cell movement. They were however, found to be significantly more damped. An additional Arnoldi analysis was performed with azimuthal wavenumber m = 1 and the resulting least damped mode had a frequency close to the experimentally observed screech frequency for the same nozzle geometry and operating condition. An animation of the evolution of the eigenmode reveals a feedback loop mechanisms that might contribute to the formation of screech tones.
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