| 1. |
- 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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| 2. |
- 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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| 3. |
- Hafsteinsson, Haukur, 1984, et al.
(författare)
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Active Suppression of Supersonic Jet Noise Using Pulsating Micro-Jets
- 2012
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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.
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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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| 4. |
- Munday, D., et al.
(författare)
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Techniques for supersonic turbojet noise reduction
- 2012
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Ingår i: ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, GT 2012; Copenhagen; Denmark; 11 June 2012 through 15 June 2012. - 9780791844670 ; 1, s. 51-56
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Konferensbidrag (refereegranskat)abstract
- Observations and simulations are presented of a supersonic jet from a nozzle representative of high-performance military aircraft such as the Saab Gripen. The nozzle has a design Mach number of 1.56 and is examined at its design condition with a surrounding secondary flow at Mach numbers of 0.0, 0.1 and 0.3. Chevrons and internal fluidic injection by microjets each reduce the noise generated by the main jet. Copyright © 2012 by ASME.
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