Experiments on Exhaust Noise of Tightly Integrated Propulsion Systems

Bridges, Jackie; Brown, Clifford A.; Bozak, Richard F.

doi:10.2514/6.2014-2904

Cited by 26 publications

(30 citation statements)

References 13 publications

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“…For round and 2:1 and 8:1 rectangular twin jets at their closest spacings, turbulence levels between the two jets decreased about 10% due to enhanced jet mixing at near static conditions. This decrease in TKE corresponds with a decrease in SPL shown in acoustic measurements 1,2,3,4 . When M f is increased to 0.25, the flow around the twin jet model creates a velocity deficit between the two nozzles.…”

Section: Discussionmentioning

confidence: 60%

“…In addition to far-field acoustic measurements, phased array and mean flow field measurements were obtained 2 . Recently, another series of experiments were performed at NASA Glenn Research Center to include more nearby surface variation as well as the effect of twin rectangular nozzles 3 . This set of experiments included far-field acoustic measurements 4 and Particle Image Velocimetry (PIV) measurements.…”

Section: Introductionmentioning

confidence: 99%

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Subsonic Round and Rectangular Twin Jet Flow Effects

Bozak

Wernet²

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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Subsonic and supersonic aircraft concepts proposed by NASA's Fundamental Aeronautics Program have integrated propulsion systems with asymmetric nozzles. The asymmetry in the exhaust of these propulsion systems creates asymmetric flow and acoustic fields. The flow asymmetries investigated in the current study are from two parallel round, 2:1, and 8:1 aspect ratio rectangular jets at the same nozzle conditions. The flow field was measured with streamwise and cross-stream particle image velocimetry (PIV). A large dataset of single and twin jet flow field measurements was acquired at subsonic jet conditions. The effects of twin jet spacing and forward flight were investigated. For round, 2:1, and 8:1 rectangular twin jets at their closest spacings, peak turbulence levels between the two jets decreased approximately 10% due to enhanced jet mixing at near static conditions. When the flight Mach number was increased to 0.25, the flow around the twin jet model created a velocity deficit between the two nozzles. This velocity deficit diminished the effect of forward flight causing an increase in turbulent kinetic energy relative to a single jet. Both of these twin jet flow field effects decreased with increasing twin jet spacing relative to a single jet. These variations in turbulent kinetic energy correlate with changes in far-field sound pressure level. Nomenclature s = Twin jet spacing, center-to-center, inches D = Nozzle diameter, inches x, y ,z = Distance from the nozzle exit, inches u = Axial velocity, inches per second U j = Ideally-expanded jet velocity, inches per second M a = Jet acoustic Mach number M f = Flight Mach number T sr = Jet static temperature ratio TKE = Turbulent kinetic energy, in 2 /sec 2 SPL = Sound pressure level, dB ref. 20μPa

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Section: Discussionmentioning

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Subsonic Round and Rectangular Twin Jet Flow Effects

Bozak

Wernet²

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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“…In this section we show results from three--dimensional SolidWorks® Flow Simulations [36]& [37] of jet flows with acoustic Mach numbers, Ma = (0.5,0.7,0.9) through rectangular jet nozzles of aspect ratios, AR = (2,4,8) in the vincity of a flat plate trailing edge. The SolidWorks® Flow Simulation automatic gridding program provides a way to mesh and solve the flow field around complex geometries and is, therefore, rather convenient for the jet surface interaction problem and was used by Bridges & Wernet [70], amoung others.…”

Section: Reynolds--averaged Navier--stokes (Rans) Calculationsmentioning

confidence: 99%

“…( y 2 ;ω ,k 3 ) = A(( y 2 − y d )2 ;ω ,k3 ) + ( y 2 − y d )B(( y 2 − y d ) 2 ;ω ,k 3 ) (A.22)where the spanwise--temporal Fourier transform isΩ ( y 2 ;ω ,k 3 ) ≡ 1 (2π ) 2 lim T →∞ e iω ( z− y 3 k 3 ω ) −T T ∫ ! ω c (z, y T ) dz −∞ ∞ ∫dy3 , (A.23) and where B = O( y d −1 ) in order that (A.22) remain dimensionless.…”

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Effect of de-correlating turbulence on the low frequency decay of jet-surface interaction noise in sub-sonic unheated air jets using a CFD-based approach

Afsar

Leib

Bozak

2017

Journal of Sound and Vibration

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In this paper we extend the Rapid-distortion theory (RDT)-based model derived by Goldstein, Afsar & Leib (J. Fluid Mech., vol. 736, pp. 532-569, 2013) for the sound generated by the interaction of a large-aspect-ratio rectangular jet with the trailing edge of a flat plate to include a more realistic upstream turbulence spectrum that possess a de-correlation (i.e. negative dip) in its space-time structure and use results from three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions to determine the mean flow, turbulent kinetic energy and turbulence length & time scales. Since the interaction noise dominates the low-frequency portion of the spectrum, we use an appropriate asymptotic approximation for the Rayleigh equation Green’s function, which enters the analysis, based on a two-dimensional mean flow representation for the jet. We use the model to predict jet-surface interaction noise for a range of subsonic acoustic Mach number jets, nozzle aspect ratios, streamwise and transverse trailing-edge locations and compare them with experimental data. The RANS meanflow computations are also compared with flow data for selected cases to assess their validity. We find that finite de-correlation in the turbulence spectrum increases the low-frequency algebraic decay (the low-frequency “roll-off”) of the acoustic spectrum with angular frequency to give a model that has a pure dipole frequency scaling. This gives better agreement with noise data compared to Goldstein et al. (2013) for Strouhal numbers less than the peak jet-surface interaction noise. For example, through sensitivity analysis we find that there is a difference of 10 dB at the lowest frequency for which data exists (relative to a model without de-correlation effects included) for the highest acoustic Mach number case. Secondly, our results for the planar flow theory provide a first estimate of the low-frequency amplification due to the jet-surface interaction for moderate aspect ratio nozzles when RANS meanflow quantities are used appropriately. This work will hopefully add to noise prediction efforts for aircraft configurations in which the exhaust systems are tightly integrated with the airframe

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“…Thus, while detailed experiments on jet-surface interaction simulating realistic flight situations were conducted in the AAPL (Bridges, Brown & Bozak 2014;Brown & Wernet 2014), the resonance phenomenon was pursued further in the smaller facility. The latter study involved the simple geometry of a rectangular flat plate of large width placed on one side of the jet.…”

Section: Introductionmentioning

confidence: 99%

An experimental investigation of resonant interaction of a rectangular jet with a flat plate

et al. 2015

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The interaction between an 8:1 aspect ratio rectangular jet and a flat plate, placed parallel to the jet, is addressed in this study. At high subsonic conditions and for certain relative locations of the plate, a resonance takes place with accompanying audible tones. Even when the tone is not audible the sound pressure level spectra are often marked by conspicuous peaks. The frequencies of these peaks, as functions of the plate's length, its location relative to the jet as well as jet Mach number, are studied in an effort to understand the flow mechanism. It is demonstrated that the tones are not due to a simple feedback between the nozzle exit and the plate's trailing edge; the leading edge also comes into play in determining the frequency. With parametric variation, it is found that there is an order in the most energetic spectral peaks; their frequencies cluster in distinct bands. The lowest frequency band is explained by an acoustic feedback involving diffraction at the plate's leading edge. Under the resonant condition, a periodic flapping motion of the jet column is seen when viewed in a direction parallel to the plate. Phase-averaged Mach number data on a cross-stream plane near the plate's trailing edge illustrate that the jet cross-section goes through large contortions within the period of the tone. Farther downstream a clear 'axis switching' takes place for the time-averaged cross-section of the jet that does not occur otherwise for a non-resonant condition.

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Experiments on Exhaust Noise of Tightly Integrated Propulsion Systems

Cited by 26 publications

References 13 publications

Subsonic Round and Rectangular Twin Jet Flow Effects

Subsonic Round and Rectangular Twin Jet Flow Effects

Effect of de-correlating turbulence on the low frequency decay of jet-surface interaction noise in sub-sonic unheated air jets using a CFD-based approach

An experimental investigation of resonant interaction of a rectangular jet with a flat plate

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