Direct Computation of Jet Noise Produced by Large-Scale Axisymmetric Structures

2000 ◽  
Vol 16 (2) ◽  
pp. 207-215 ◽  
Author(s):  
R. R. Mankbadi ◽  
S. H. Shih ◽  
R. Hixon ◽  
L. A. Povinelli
Keyword(s):  
Large Scale ◽  
Jet Noise ◽  
Direct Computation ◽  
Axisymmetric Structures

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

2021 ◽  
Vol 20 (1-2) ◽  
pp. 4-34
Author(s):  
Reda R Mankbadi ◽  
Saman Salehian
Keyword(s):  
Large Scale ◽  
Flat Surface ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Dominant Frequency ◽  
Wavy Surface ◽  
Initial Region ◽  
Reflected Waves ◽  
Free Jet

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

scholarly journals Anisotropic source modelling for turbulent jet noise prediction

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190075 ◽  
Author(s):  
Xihai Xu ◽  
Xiaodong Li
Keyword(s):  
Large Scale ◽  
Noise Source ◽  
Jet Noise ◽  
Source Model ◽  
Noise Prediction ◽  
Reynolds Stresses ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Navier Stokes Equation ◽  
Anisotropic Source

An anisotropic component of the jet noise source model for the Reynolds-averaged Navier–Stokes equation-based jet noise prediction method is proposed. The modelling is based on Goldstein's generalized acoustic analogy, and both the fine-scale and large-scale turbulent noise sources are considered. To model the anisotropic characteristics of jet noise source, the Reynolds stress tensor is used in place of the turbulent kinetic energy. The Launder–Reece–Rodi model (LRR), combined with Menter's ω -equation for the length scale, with modified coefficients developed by the present authors, is used to calculate the mean flow velocities and Reynolds stresses accurately. Comparison between predicted results and acoustic data has been carried out to verify the accuracy of the new anisotropic source model. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

The role of shear-layer instability waves in jet exhaust noise

1977 ◽  
Vol 80 (2) ◽  
pp. 321-367 ◽  
Author(s):  
C. J. Moore
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Broad Band ◽  
Jet Noise ◽  
Acoustic Power ◽  
Thermal Fluctuations ◽  
Excess Noise ◽  
Number Range ◽  
Instability Waves ◽  
Noise Measurements

Large-scale structures in the form of instability waves are an inherent part of a shearlayer mixing process. Such structures are shown to be present in an acoustically and aerodynamically well behaved jet even at high Mach numbers. They do not directly radiate significant acoustic power in a subsonic jet, but do govern the production of the turbulent fluctuations which radiate broad-band jet noise. Over the whole subsonic Mach number range, a significant increase in jet noise can be produced by exciting the shear layer with a fluctuating pressure at the nozzle of only 0·08 % of the jet dynamic head but with the correct Strouhal number. Such excitation by internal acoustic, aerodynamic or thermal fluctuations could explain the variability of jet noise measurements between different rigs and could also be responsible for some components of ‘excess’ noise.

Far-field noise of a subsonic jet under controlled excitation

1985 ◽  
Vol 152 ◽  
pp. 83-111 ◽  
Author(s):  
K. B. M. Q. Zaman
Keyword(s):  
Flow Field ◽  
Shear Layer ◽  
Strouhal Number ◽  
Large Scale ◽  
Jet Noise ◽  
Large Scale Structure ◽  
Broadband Noise ◽  
Scale Structure ◽  
Initial Condition ◽  
High Speeds

The phenomena of excitation-induced suppression and amplification of broadband jet noise have been experimentally investigated in an effort to understand the mechanisms, especially in relation to the near flow-field large-scale structure dynamics. Suppression is found to occur only in jets at low speeds with laminar exit boundary layers, the optimum occurring for excitation at Stθ ≈ 0.017, where Stθ is the Strouhal number based on the initial shear-layer momentum thickness. The suppression mechanism is linked to an initial-condition effect on the large-scale structure dynamics. The interaction and evolution of laminar-like structures at low jet speeds produce more (normalized) noise and turbulence, compared to asymptotically lower levels at high speeds when the initial shear layer is no longer laminar. The effect of initial condition has been demonstrated by tripped versus untripped jet data. The excitation at Stθ ≈ 0.017 results in a quick roll-up and transition of the laminar shear-layer vortices, yielding coherent structures which are similar to those at high speeds. Thus, the broadband noise and turbulence are suppressed, but at the most to the asymptotically lower levels. When at the asymptotic level, the broadband jet noise can only be amplified by the excitation; the amplification is found to be maximum for excitation in the StD range of 0.65–0.85, StD being the Strouhal number based on the jet diameter. Excitation in this StD range also produces strongest vortexpairing activity. From spectral analysis of the flow-field and the near sound-pressure field, it is inferred that the pairing process induced by the excitation is at the origin of the broadband noise amplification.

The noise from the large-scale structure of a jet

1978 ◽  
Vol 84 (4) ◽  
pp. 673-694 ◽  
Author(s):  
J. E. Ffowcs Williams ◽  
A. J. Kempton
Keyword(s):  
Experimental Data ◽  
Shear Layer ◽  
Large Scale ◽  
Noise Source ◽  
Broad Band ◽  
Jet Noise ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Dominant Contribution ◽  
Excitation Field

In this paper we assess the importance as a noise source of the well-ordered large-scale structure of a jet. We propose two simple models of the structure: the first emphasizes those features in common with waves that initially grow on an unstable shear layer but eventually saturate and decay, while the second regards the abrupt pairing of eddies as the most significant event in the jet's development. Our models demonstrate the possibility that forcing at one frequency could increase the broad-band noise of a jet, though, for jets with supersonic eddy convection velocities, the sound propagating in the direction of the Mach angle retains the spectrum of the excitation field. These features are consistent with the available experimental data, and strongly support the view that the large-scale structure of jet turbulence provides the dominant contribution to jet noise.

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