Rough Wall Boundary Layer Noise: Theoretical Predictions

Glegg, Stewart; Devenport, William J.; Grissom, Dustin L.; Smith, Benjamin S.

doi:10.2514/6.2007-3417

Cited by 13 publications

(3 citation statements)

References 6 publications

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“…Conceptually, the new understanding of acoustic source mechanisms can help identify physically important sources to model and eliminate unimportant noise sources. For example, vortex shedding from roughness elements used to be viewed as a dominant noise source and modelled in terms of bluff-body vortex shedding in a free stream (Smol'yakov 2001;Glegg et al 2007). The computational results suggest, however, that vortex shedding is unimportant as a source of self-noise and should not be modelled as such, but its role in enhancing Q. Yang and M. Wang near-wall turbulence and thereby the noise from downstream elements needs to be considered.…”

Section: Further Discussionmentioning

confidence: 99%

Boundary-layer noise induced by arrays of roughness elements

Yang

Wang

2013

J. Fluid Mech.

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Sound induced by arrays of 10 × 4 roughness elements in low-Mach-number turbulent boundary layers at Re θ = 3065 is studied with Lighthill's theory and large-eddy simulation. Three roughness fetches consisting of hemispheres, cuboids and short cylinders are considered. The roughness elements of different shapes have the same height of 0.124δ, the same element-to-element spacing of 0.727δ and the same flow blockage area. The acoustically compact roughness elements and their images in the wall radiate sound primarily as acoustic dipoles in the plane of wall. The dipole strength, orientation and spatial distribution show strong dependence on the roughness shape. Correlations between dipole sources associated with neighbouring elements are found to be small for these sparsely distributed roughness arrays. Correlations and coherence between roughness dipoles and surface pressure fluctuations are analysed, which reveals the importance of the impingement of upstream turbulence and surrounding vortical structures to dipole sound radiation, especially in the streamwise direction. For roughness shapes with sharp frontal edges, the edge-induced unsteady separation and reattachment also play important roles in sound generation. Large-scale turbulent structures in the boundary layer have a relatively low influence on roughness dipoles, except for the first row of elements.

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Section: Further Discussionmentioning

confidence: 99%

Boundary-layer noise induced by arrays of roughness elements

Yang

Wang

2013

J. Fluid Mech.

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“…According to the previous works [20][21][22][23] , there might be two mechanisms governing the noise generation when turbulent flows experience discontinuities on a plate: diffraction of the incoming turbulence and turbulence modification. The former refers to the diffraction process that hydrodynamic pressure fluctuations are efficiently converted into acoustic energies by surface inhomogeneity.…”

Section: Noise Mechanismsmentioning

confidence: 99%

An experimental study of aerodynamic noise from large obstructions in turbulent boundary layer flows

Sundeep

Zhou

et al. 2022

Physics of Fluids

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This paper reports an experimental study on the aerodynamic noise generated by a two-dimensional large obstacle in a turbulent boundary layer. Square and triangular obstacles with varying heights of h/δ=0.48,0.8,1.2,1.6, and 2 (where δ is the boundary layer thickness measured without the obstacle present) are tested at various flow speeds ranging from 20 to 50 m/s. The Reynolds number based on step height and free stream velocity ranged between 7500 and 79 000. A linear microphone array is arranged aside to measure the sound radiation in the spanwise direction. It is suggested that both square and triangular obstructions can lead to a broadband source with a dipole-type directivity. A consistent increase in the noise strength is observed with obstacle height and flow speed. The underlying noise source is revealed by comparing the acoustic spectra of different obstacle geometries. The low-frequency noise is contributed by the turbulence modification due to the flow impingement onto the obstacle, while the high-frequency sound is mainly caused by the diffraction of hydrodynamic pressure by the sharp leading edge.

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“…Howe 8 made this prediction by relating the wall wavenumber pressure spectrum to the acoustic spectrum. Turbulent boundary layers near rough walls were examined by Glegg et al, 9 in a similar way to that of Howe, 8 by defining two additional sound sources for the noise generation. The wall wavenumber pressure spectrum was used like in Howe, 8 as well as a correlation function for the surface roughness distribution.…”

Section: Introductionmentioning

confidence: 99%

The Prediction of Noise from Turbulent Boundary Layers Attached to Porous Media

Pager

Miller

2018

2018 AIAA/CEAS Aeroacoustics Conference

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Aerospace vehicles, wind tunnel test section walls, and other structures often contain porosity that alters the turbulent boundary layer and radiated noise. A semi-empirical mathematical model is developed to predict and analyze the acoustic radiation from turbulent boundary layers over porous media. The model is an acoustic analogy that depends on local flow-field statistics. These statistics are calculated through a steady Reynoldsaveraged Navier-Stokes computational fluid dynamics solver that includes porous material. Acoustic predictions are conducted for four subsonic Mach numbers without a pressure gradient. At each Mach number, four porosities with constant liner depth and porous turbulent length scale are examined along with the non-porous solution. The flow-field is validated through comparison with acoustic measurement. Predictions are conducted to ascertain changes in acoustic radiation with varying porosity. We find that noise is amplified or reduced in a non-intuitive way with the introduction of porosity, variation of frequency, and increase of Mach number.

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Rough Wall Boundary Layer Noise: Theoretical Predictions

Cited by 13 publications

References 6 publications

Boundary-layer noise induced by arrays of roughness elements

Boundary-layer noise induced by arrays of roughness elements

An experimental study of aerodynamic noise from large obstructions in turbulent boundary layer flows

The Prediction of Noise from Turbulent Boundary Layers Attached to Porous Media

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