The Prediction of Broadband Shock-Associated Noise Including Propagation Effects

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A physical explanation for the saturation of broadband shock-associated noise (BBSAN) intensity with increasing jet stagnation temperature has eluded investigators. An explanation is proposed for this phenomenon with the use of an acoustic analogy. For this purpose the acoustic analogy of Morris and Miller is examined. To isolate the relevant physics, the scaling of BBSAN at the peak intensity level at the sideline (ψ = 90 degrees) observer location is examined. Scaling terms are isolated from the acoustic analogy and the result is compared using a convergent nozzle with the experiments of Bridges and Brown and using a convergent-divergent nozzle with the experiments of Kuo, McLaughlin, and Morris at four nozzle pressure ratios in increments of total temperature ratios from one to four. The equivalent source within the framework of the acoustic analogy for BBSAN is based on local field quantities at shock wave shear layer interactions. The equivalent source combined with accurate calculations of the propagation of sound through the jet shear layer, using an adjoint vector Green's function solver of the linearized Euler equations, allows for predictions that retain the scaling with respect to stagnation pressure and allows for the accurate saturation of BBSAN with increasing stagnation temperature. This is a minor change to the source model relative to the previously developed models. The full development of the scaling term is shown. The sources and vector Green's function solver are informed by steady Reynolds-Averaged Navier-Stokes solutions. These solutions are examined as a function of stagnation temperature at the first shock wave shear layer interaction. It is discovered that saturation of BBSAN with increasing jet stagnation temperature occurs due to a balance between the amplification of the sound propagation through the shear layer and the source term scaling. Component of the vector Green's function of the linearized Euler equations xStreamwise direction x = x(x, y, z)Vector observer position y = y(x, y, z)Vector source position from the primary nozzle exit β Off-design parameter γ Ratio of specific heats δ Dirac delta function ǫ Dissipation rate of turbulent kinetic energy η = η (ξ, η, σ) Vector between two source locations λ Parameter equal to ω sin θ/c ∞ π IntroductionAircraft, rockets, and many other vehicles use jet engines as their means of propulsion. The noise produced by jet plumes is often problematic both physically 1 and psychologically. 2 For example, civilian and military aircraft operating in the vicinity of airports can be an annoyance to the community 3 due to jet noise. During take-off, noise from the jet exhaust often dominates other aircraft noise sources.4 High speed supersonic jet flows cause hearing loss for military personnel during carrier landing and take-off and on military practice fields.5 If aircraft cruise a component of the cabin noise is due to jet noise. The loading induced by jet noise can cause sonic fatigue on aircraft and rocket engines.1 Rockets used to place...

Section: Mathematical Analysismentioning

confidence: 99%

The Scaling of Broadband Shock-Associated Noise with Increasing Temperature

Miller

2015

Self Cite

“…BBSAN is an upstream propagating broadband component generated when the turbulent eddies pass through shock cells (8). The radiation from the subsequent shock wave shear layer interaction combines constructively and is characterized by multiple broad spectral lobes (9). When considering the far-field noise, BBSAN is dominant at mid-to high-frequencies in the upstream and sideline directions relative to the jet flow (10).…”

Section: Introductionmentioning

confidence: 99%

Jet noise sources for chevron nozzles in under-expanded condition

Jawahar

Meloni

Camussi

2022

Imperfectly expanded jet flows are known to have additional noise sources known as Screech and broadband shock-associated noise. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock cell structures. In this study, thorough experimental investigations were carried out on chevron nozzles to assess the importance of chevron parameters such as the chevron count and chevron penetration angle on the pressure field emitted by the jet. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as pressure spectra, directivity and overall sound pressure levels along with near-field measurements were acquired for jet Mach numbers ranging from M = 1.1–1.4. Fourier-based and Wavelet-based analyses were used to highlight the different features of the various tested nozzles. Wavelet decomposition results highlight that the presence of the chevrons reduce the acoustic noise especially at a higher axial distance with increased levels of noise reduction achieved by chevron nozzle with deep penetration angle.

“…Norum and Seiner 13 related the peak frequency of the BBSAN to the eddy convective velocity and the shock cell length scale. Further predictions were made by Tam 14 using a stochastic model based on an empirical correlation of experimental measurements, as well as by Miller and Morris 15 using an acoustic analogy. The corrugations work to reduce the BBSAN through a lowering of the pressure imbalance and weakening of the shock structure.…”

Section: Introductionmentioning

confidence: 99%

Acoustics measurements of military-style supersonic beveled nozzle jets with interior corrugations

Powers

McLaughlin

2016

Increasingly powerful and noisy military aircraft have generated the need for research leading to the development of supersonic jet noise reduction devices. The hot, high speed supersonic jets exhausting from military aircraft during takeoff present a most challenging problem. The present study extends prior research on two methods of noise reduction. The first is the internal nozzle corrugations pioneered by Seiner et al. and the second is the beveled exit plane explored most recently by Viswanathan. A novel research idea of creating fluidic corrugations similar to the nozzle corrugations has been initiated by Penn State. To further the understanding and analysis of the fluidic corrugations, the present study focuses on the flow field and acoustic field of nozzles with two, three, and six conventional, hardwalled corrugations. The effect of the combination of the internal corrugations with a beveled nozzle is explored. The results show that significant noise reductions of over 3 dB of the mixing noise and the broadband shock-associated noise can be achieved. The combination of the beveled nozzle and the internal nozzle corrugations showed that there is less azimuthal dependence of the acoustic field than for the purely beveled nozzle. The combination nozzle was shown to reduce the noise over a wider range of polar angles and operating conditions than either the purely beveled nozzle or the purely corrugated nozzle.