A wavenumber approach to modelling the response of a randomly excited panel, part i: general theory

Flight test measurement of exterior turbulent boundary layer pressure fluctuations on Boeing model 737 airplane

Low wavenumber wall pressure measurements using a rectangular membrane as a spatial filter

Noise generated by low pressure axial flow fans, I: Modeling of the turbulent noise

The aerodynamic flow and fluctuating surface pressure of a plane, turbulent, twodimensional wall jet flow into still air over smooth and rough surfaces has been investigated in a recently constructed wall jet wind tunnel testing facility. The facility has been shown to produce a wall jet flow with Reynolds numbers based on the momentum thickness, , of between 395 and 1100 and nozzle exit Reynolds numbers, , of between 16000 and 45000. The wall jet flow properties (δ, δ, θ, y1/2, Um, u, etc.) were measured and characterized over a wide range of initial flow conditions and measurement locations relative to the wall jet source. These flow properties were measured for flow over a smooth flow surface and for flow over roughness patches of finite extent. The patches used in the current study varied in length from 305 mm to 914 mm (between 24 and 72 times the nozzle height, b) and were placed so that the leading edge of the patch was fixed at 1257 mm (x/b = 99) downstream of the wall jet source. These roughness patches were of a random sand grain roughness type and the roughness grain size was varied throughout this experiment. The tests covered roughness Reynolds numbers (k) ranging from less than 2 to over 158 (covering the entire range of rough wall flow regimes from hydrodynamically smooth to fully rough). For the wall jet flows over 305 mm long patches of roughness, the displacement and momentum thicknesses were found to vary noticeably with the roughness grain size, but the maximum velocity, mixing layer length scale, y1/2, and the boundary layer thickness were not seen to vary in a consistent, determinable way. Velocity spectra taken at a range of initial flow conditions and at several distinct heights above the flow surface showed a limited scaling dependency on the skin friction velocity near the flow surface. The spectral density of the surface pressure of the wall jet flow, which is not believed to have been previously investigated for smooth or rough surfaces, showed distinct differences with that seen in a conventional boundary layer flow, especially at low frequencies. This difference is believed to be due to the presence of a mixing layer in the wall jet flow. Both the spectral shape and level were heavily affected by the variation in roughness grain size. This effect was most notable in overlap region of the spectrum. Attempts to scale the wall jet surface pressure spectra using outer and inner variables were successful for the smooth wall flows. The scaling of the rough wall jet flow surface pressure proved to be much more difficult, and conventional scaling techniques used for ordinary turbulent boundary layer surface pressure spectra were not able to account for the changes in roughness present during the current study. An empirical scaling scheme was proposed, but was only marginally effective at scaling the rough wall surface pressure.

Wall Jet Boundary Layer Flows Over Smooth and Rough Surfaces

This paper reports measurements of the cross‐spectral density of the wall‐pressure fluctuations beneath a turbulent boundary layer for three different surface‐roughness conditions. The roughness consisted of sparsely populated, uniformly distributed sand particles—each roughness being distinguished by the sand‐particle size. Separate studies of the spectral density and of the lateral and longitudinal narrow‐band normalized space‐time correlations were made in order to determine the cross‐spectral density of the wall‐pressure fluctuations. The results indicate that only the spectral density is strongly dependent on roughness size, for the roughnesses examined. To relate quantitatively the spectral densities measured on each surface, the roughness was characterized in terms of Nikuradse's equivalent sand‐roughness parameter. The spectral density was then normalized, using this roughness parameter, the shear velocity, and the local coefficient of skin friction. Also, for the roughest surface, the pressure fluctuations in the vicinity of a particle and the correlation of these fluctuations with pressure fluctuations at some distance from the particle were examined in order to determine any observable effects of the local flow about the particles. The results indicate that the local flow can be ignored, provided that the roughness size is not too large. The measurements do not reveal any direct relation between the cross‐spectral densities measured on rough surfaces with those measured on smooth.

Effects of roughness on measured wall-pressure fluctuations beneath a turbulent boundary layer

Acoustic radiation from plates excited by flow noise

On the utilization of a flexible beam as a spatial filter

Aerial noise measurement methods may be well suited to the determination of spatially averaged traffic noise exposure levels, and could possibly be used as a means of assessing the long‐term effectiveness of motor vehicle noise regulations. In this study two theoretical models are developed for some specific aerial measurement situations. Several characteristics of the models are examined. Limited experimental measurements agree well with theoretically predicted results; elevated measured noise levels are nearly proportional to the density of the traffic (in vehicles per unit area) on the city streets.

R. F. Lambert

Papers

Effects of roughness on measured wall-pressure fluctuations beneath a turbulent boundary layer

Acoustic radiation from plates excited by flow noise

On the utilization of a flexible beam as a spatial filter

Elevated measurement of traffic noise above an ideal reverberant city

Elevated measurement of traffic noise above an ideal reverberant city