Recent Developments in the Application of the Generalized Acoustic Analogy to Jet Noise Prediction

Goldstein, M. E.

doi:10.1260/1475-472x.10.2-3.89

Cited by 8 publications

(3 citation statements)

References 37 publications

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“…For example, one of the early approaches based on Lilley's (1972) equation, which is still used in modern noise prediction codes (Khavaran, Bridges & Georgiadis 2005), explicitly accounts for sound interaction with a simplified jet mean flow. More discussion on acoustic analogy methods can be also found in Morris & Farassat (2002), Tam et al (2008), Michel (2009), Morris (2009), Karabasov (2010 and Goldstein (2011).…”

Section: Introductionmentioning

confidence: 99%

An investigation of the mechanisms of sound generation in initially laminar subsonic jets using the Goldstein acoustic analogy

2013

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The details of the sound sources within two initially laminar subsonic jets corresponding to different inflow conditions, one fully laminar and the other with nozzle boundary layer forcing, are studied using the Goldstein acoustic analogy. The statistics of the acoustic analogy equivalent sources are generated from large eddy simulations (LES) and issues associated with the range of validity of these are explored. The predicted comparative importance of various source terms confirms the results of previous studies, with the exception of one extra term that involves the longitudinal and the lateral source components. Agreement within 1 dB over the frequency range from Strouhal number $\mathit{St}= 0. 8$ to $\mathit{St}= 6$, which was shown to best correspond to the validity range of the acoustic source model for the LES data available, is found between noise predictions using the acoustic analogy model and those of a previously conducted LES–ILEE (isotropic linearized Euler equation) control surface method for the nominally laminar inflow jet case. The acoustic analogy is used to determine the source length scales which contribute to noise at different radiated angles to the jet, how they are distributed and how they change with change of inflow conditions. For the vortex pairing frequency, using a new acoustic source decomposition technique based on the correlation length scale, two types of noise sources are found. One source, which corresponds to the peak source amplitude, is located at the upstream end of the jet and is associated with the vortex pairing. The other one, which is the dominant source, is associated with jet mixing at the end of the jet potential core. It is also shown that boundary layer forcing leads to a reduction in the contribution to the noise of the large source length scales in comparison with the fully laminar case.

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Section: Introductionmentioning

confidence: 99%

An investigation of the mechanisms of sound generation in initially laminar subsonic jets using the Goldstein acoustic analogy

2013

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“…Note that the latter (4x3) tensor includes both the fluctuating Reynolds stresses and the fluctuating enthalpy vector. This is the same term that appears as a separate source component in other formulations of the generalised acoustic analogy (Goldstein 2002(Goldstein , 2003(Goldstein , 2011.…”

Section: Introductionmentioning

confidence: 91%

A volume integral implementation of the Goldstein generalised acoustic analogy for unsteady flow simulations

Semiletov

Karabasov

2018

J. Fluid Mech.

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A new volume integral method based on the Goldstein generalised acoustic analogy is developed and directly applied with large-eddy simulation (LES). In comparison with the existing Goldstein generalised acoustic analogy implementations, the current method does not require the computation and recording of the expensive fluctuating stress autocovariance function in the seven-dimensional space–time. Until now, the multidimensional complexity of the generalised acoustic analogy source term has been the main barrier to using it in routine engineering calculations. The new method only requires local pointwise stresses as an input that can be routinely computed during the flow simulation. On the other hand, the new method is mathematically equivalent to the original Goldstein acoustic analogy formulation, and, thus, allows for a direct correspondence between different effective noise sources in the jet and the far-field noise spectra. The implementation is performed for conditions of a high-speed subsonic isothermal jet corresponding to the Rolls-Royce SILOET experiment and uses the LES solution based on the CABARET solver. The flow and noise solutions are validated by comparison with experiment. The accuracy and robustness of the integral volume implementation of the generalised acoustic analogy are compared with those based on the standard Ffowcs Williams–Hawkings surface integral method and the conventional Lighthill acoustic analogy. As a demonstration of its capabilities to investigate jet noise mechanisms, the new integral volume method is applied to analyse the relative importance of various noise generation and propagation components within the Goldstein generalised acoustic analogy model.

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“…The far-field pressure spectrum can be expressed in terms of the two-point time-delayed correlation of the stress tensor, a statistical property that may be supplied using computational data for the near field of the flow. Applications of this generalised analogy indeed led to improved predictions of jet noise (Goldstein 2011;Afsar, Sescu & Leib 2019a;Afsar, Sescu & Sassanis 2019b). However, the acoustic analogy type of approach does not provide an unambiguous identification of the physical sources, as remarked by Goldstein (2003).…”

Section: Introductionmentioning

confidence: 99%

Nonlinear evolution and low-frequency acoustic radiation of ring-mode coherent structures on subsonic turbulent circular jets

Zhang

2022

J. Fluid Mech.

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By adapting the triple decomposition of an instantaneous turbulent flow into a time-averaged mean field, large-scale coherent motion and fine-scale random fluctuations, and treating the coherent motion as instability modes on the mean flow, a mathematical theory is developed to describe the nonlinear spatial–temporal modulation and acoustic radiation of a coherent structure (CS) on a circular jet in the form of a wavepacket consisting of an axisymmetric (ring) mode and its sideband components. The effect of fine-scale turbulence on the CS is characterised via a gradient closure model, and the non-parallelism due to the axial variation and radial velocity of the mean flow is taken into account. By employing the matched asymptotic expansion and multi-scale techniques, a strongly nonlinear system is derived, which governs the envelope of the CS and its vorticity and temperature in the critical layer. Numerical solutions to the evolution system show that the theory captures the nonlinear amplitude attenuation and vorticity roll-up as observed in experiments. The large-distance asymptotic properties of the CS allow us to describe and predict its acoustic radiation on the basis of first principles. The CS is trapped within the jet, but its self-interaction generates a temporally and axially modulated mean-flow distortion, which acts as the emitter to radiate low-frequency sound waves, with the Reynolds stresses driving this mean-flow distortion being identified unambiguously to be the physical source in the present context. An equivalent source in the Lighthill type of acoustic analogy is also identified. For the present ring-mode CS in the fully developed region of a circular jet, the equivalent source can be determined before the acoustic field is, and the intensity of the radiated sound waves is found to be $O(\epsilon ^3)$ , where $\epsilon$ measures the magnitude of the CS. The directivity and spectrum of the acoustic far field are calculated for representative parameters, and the predicted features resemble experimental measurements.

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Recent Developments in the Application of the Generalized Acoustic Analogy to Jet Noise Prediction

Cited by 8 publications

References 37 publications

An investigation of the mechanisms of sound generation in initially laminar subsonic jets using the Goldstein acoustic analogy

An investigation of the mechanisms of sound generation in initially laminar subsonic jets using the Goldstein acoustic analogy

A volume integral implementation of the Goldstein generalised acoustic analogy for unsteady flow simulations

Nonlinear evolution and low-frequency acoustic radiation of ring-mode coherent structures on subsonic turbulent circular jets

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