Measurements of roughness noise

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

doi:10.1016/j.jsv.2011.03.017

Cited by 50 publications

(17 citation statements)

References 21 publications

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“…The second surface, pictured in Figure 5b, was formed by a sheet of 20-grit sandpaper roughness extending 200 mm streamwise and 600 mm spanwise. This type of surface, tested previously by Devenport et al 13 , has a nominal grain size of 0.95 mm, a grain density of 0.23 grains/mm 2 , and an RMS roughness height of 0.206 mm. The edges of these roughness patches were taped and faired to the surrounding wall using 0.12 mm thick aluminum tape.…”

Section: Rough Surfacesmentioning

confidence: 98%

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Bio-inspired canopies for the reduction of roughness noise

Clark

Daly

Devenport

et al. 2016

Journal of Sound and Vibration

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This work takes inspiration from the structure of the down covering the flight feathers of larger species of owls, which contributes to their ability to fly almost silently at frequencies above 1.6 kHz. Microscope photographs of the down show that it consists of hairs that form a structure similar to that of a forest. The hairs initially rise almost perpendicular to the feather surface but then bend over in the flow direction to form a canopy with an open area ratio of about 70%. Experiments have been performed to examine the noise radiated by a large open area ratio canopy suspended above a surface. The canopy is found to dramatically reduce pressure fluctuations on the underlying surface. While the canopy can produce its own sound, particularly at high frequencies, the reduction in surface pressure fluctuations can reduce the noise scattered from an underlying rough surface at lower frequencies. A theoretical model is developed which characterizes the mechanism of surface pressure reduction as a result of the mixing layer instability of flow over forest canopies.

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Section: Rough Surfacesmentioning

confidence: 98%

“…The fabric acted as a canopy over the surface roughness in order to simulate the downy coating of the owl's feathers. The rough surfaces included two surfaces (hemispherical and sandpaper) whose roughness noise characteristics are well known from previous studies 12,13 .…”

Section: Experimental Apparatus and Instrumentationmentioning

confidence: 99%

Bio-inspired canopies for the reduction of roughness noise

Clark

Daly

Devenport

et al. 2016

Journal of Sound and Vibration

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“…However, there were significant disagreements over suggested scaling laws, controlling parameters and the physical mechanisms behind the theories. The lack of understanding and predictive tools for roughness noise prompted a number of investigations in recent years, including the study of Liu, Dowling & Shin (2006 aimed at evaluating and modelling the contribution of roughness noise to airframe noise, and a concerted effort (Blake et al 2008) consisting of theoretical Glegg & Devenport 2009), experimental (Anderson et al 2007;Smith et al 2008;Alexander et al 2009Alexander et al , 2010, 2013Devenport et al 2010Devenport et al , 2011 and numerical (Yang & Wang 2008 investigations. Liu & Dowling (2007) evaluated Howe's semi-empirical model (Howe 1998) using a number of different smooth wall pressure-spectrum theories with enhanced friction velocities and boundary-layer thicknesses to adjust for the presence of roughness, and 284 Q.…”

Section: Introductionmentioning

confidence: 99%

“…Roughness noise from short fetches of sandpaper roughness Smith et al 2008;Devenport et al 2011) as well as discrete roughness elements (Alexander et al 2009 were measured. The sandpaper noise measurements were performed at a number of flow speeds and with various roughness sizes ranging from hydrodynamically smooth to fully rough.…”

Section: Introductionmentioning

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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“…The sensing area of five of these microphones was reduced by fitting them with ½-mm pinhole caps. Previous measurements under a wall jet boundary layer, by Devenport et al (2011) showed a ½-mm pinhole to be sufficiently small enough to resolve pressure fluctuations up to 20-kHz. However, Gravante et al (1998) had a more conservative estimate on the pinhole size required to ensure sensor attenuation was not found at high frequencies.…”

Section: Wall Pressure Microphone Instrumentationmentioning

confidence: 96%

The Wall Pressure Spectrum of High Reynolds Number Rough-Wall Turbulent Boundary Layers

Forest

2011

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)

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Measurements of roughness noise

Cited by 50 publications

References 21 publications

Bio-inspired canopies for the reduction of roughness noise

Bio-inspired canopies for the reduction of roughness noise

Boundary-layer noise induced by arrays of roughness elements

The Wall Pressure Spectrum of High Reynolds Number Rough-Wall Turbulent Boundary Layers

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