Measurements of Fluctuating Wall Pressure for Separated/Reattached Boundary Layer Flows

1986 ◽  
Vol 108 (3) ◽  
pp. 301-307 ◽  
Author(s):  
T. M. Farabee ◽  
M. J. Casarella
Keyword(s):  
Boundary Layer ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Plate Boundary ◽  
Low Frequency ◽  
Wall Pressure ◽  
Boundary Layer Flows ◽  
Backward Facing Step ◽  
Wall Pressure Fluctuations ◽  
Layer Flow

Measurements were made of the wall pressure field beneath separated/reattached boundary layer flows. These flows consisted of two types; flow over a forward-facing step and flow over a backward-facing step. Wall pressure fluctuations from an equilibrium flat plate boundary layer flow were also measured and used as a baseline for comparative purposes. Values of the RMS fluctuating pressure as well as the frequency spectral density, phase velocity, and coherence of the surface pressure field were measured at various locations upstream and downstream of the steps. The experimental results show that the separation-reattachment process produces large-amplitude, low-frequency pressure fluctuations. The measured spectral statistics of the wall pressure fluctuations are consistent with the view that at reattachment there exists a region of coherent highly energized velocity fluctuations located near the wall which, as it convects downstream, decays and diffuses away from the wall. This energized region remains identifiable in the wall pressure statistics as far as 72 step heights downstream of the backward-facing step.

The scaling of the wall pressure fluctuations in polymer-modified turbulent boundary layer flow

2000 ◽  
Vol 108 (1) ◽  
pp. 71-75 ◽  
Author(s):  
Timothy A. Brungart ◽  
Wayne J. Holmberg ◽  
Arnold A. Fontaine ◽  
Steven Deutsch ◽  
Howard L. Petrie
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Flow ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Wall Pressure Fluctuations ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

An Experimental Study of the Flow and Wall Pressure Field Around a Wing-Body Junction

1986 ◽  
Vol 108 (3) ◽  
pp. 308-314 ◽  
Author(s):  
M. A. Z. Hasan ◽  
M. J. Casarella ◽  
E. P. Rood
Keyword(s):  
Pressure Gradient ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Low Frequency ◽  
Adverse Pressure Gradient ◽  
Horseshoe Vortex ◽  
Wall Pressure ◽  
Frequency Content ◽  
Wall Pressure Fluctuations

The flow and wall-pressure field around a wing-body junction has been experimentally investigated in a quiet, low-turbulence wind tunnel. Measurements were made along the centerline in front of the wing and along several spanwise locations. The flow field data indicated that the strong adverse pressure gradient on the upstream centerline causes three-dimensional flow separation at approximately one wing thickness upstream and this induced the formation of the horseshoe root vortex which wrapped around the wing and became deeply embedded within the boundary layer. The wall-pressure fluctuations were measured for their spectral content and the data indicate that the effect of the adverse pressure gradient is to increase the low-frequency content of the wall pressure and to decrease the high-frequency content. The wall pressure data in the separated region, which is dominated by the horseshoe vortex, shows a significant increase in the low-frequency content and this characteristic feature prevails around the corner of the wing. The outer edge of the horseshoe vortex is clearly identified by the locus of maximum values of RMS wall pressure.

Wall pressure fluctuations in attached boundary-layer flow

AIAA Journal ◽  
1983 ◽  
Vol 21 (4) ◽  
pp. 495-502 ◽  
Author(s):  
A. L. Laganelli ◽  
A. Martellucci ◽  
L. L. Shaw
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Wall Pressure Fluctuations ◽  
Layer Flow

Acoustic Radiation From Separated Boundary-Layer Flow Over a Rearward-Facing Step on a Flat Panel

2003 ◽  
Author(s):  
Walter A. Kargus ◽  
Gerald C. Lauchle
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Acoustic Radiation ◽  
Fluid Dynamic ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Wall Jet ◽  
Measured Velocity ◽  
Wall Pressure Fluctuations ◽  
Layer Flow

The acoustic radiation from a turbulent boundary layer that occurs downstream of a rearward facing step discontinuity and reattaches to a flat plat is considred experimentally. The step is exposed ot a zero incidence, uniform subsonic flow. a quiet wall jet facility situated in an anechoic chamber is used for the studies. The “point” wall pressure spectra are measured by small, “pinhole” microphones located at various locations under the layer, including a point directly in the 90° corner of the step. The wall pressure fluctuations measured at the various locations are correlated with the signal detected by a far-field microphone. The measured cross-spectral densities are thus used to identify the relative contributions of the various flow regimes to the direct radiation. It is shown that the separation of the flow over the corner of the step is a dominant acoustic source, which is supported not only by the measured cross spectra, but also by the favorable comparison of the measured velocity power law to the theoretical value. Measurements made where the flow reattaches and at the turbulent boundary layer are less conclusive. This is because the pinhole tube attached to the microphone produced a sound due to a fluid-dynamic oscillation, which contaminated the measurement of the aeroacoustic sources.

Measurement of turbulent boundary layer unsteady wall pressures beneath elastomer layers of various thicknesses on a plate

2021 ◽  
Vol 69 (3) ◽  
pp. 182-198
Author(s):  
Cory J. Smith ◽  
Dean E. Capone ◽  
Timothy A. Brungart ◽  
William K. Bonness
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Excellent Agreement ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Wall Pressure ◽  
Shear Stresses ◽  
Backward Facing Step ◽  
Wall Pressure Fluctuations ◽  
Velocity Statistics

The attenuation of turbulence-inducedwall pressure fluctuations through elastomer layers is studied experimentally and analytically. Wall pressure statistics are measured downstream from a backward facing step, with no elastomer present and beneath 2-, 3- and 4-mm-thick elastomers in a water tunnel facility. In the absence of an elastomer layer, the wall pressure spectra, cross-spectra and velocity statistics measured at the various locations downstream from the backward facing step are in excellent agreement with those reported in the archival literature. The streamwise coherence measured beneath the elastomer layers is higher than that measured in the absence of an elastomer layer, an effect which increases with increasing elastomer thickness. It is speculated that this increase in coherence level is due to the ability of the elastomer to support shear stresses, which effectively increases the area over which an eddy influences the normal stresses measured by the pressure sensors. The high-frequency filtering of the elastomers is also observed in the coherence at the smallest streamwise separation. The attenuation of the turbulent boundary layer wall pressure fluctuations through the elastomer layer using an analytical elastomer transfer function is in excellent agreement with the attenuation measured experimentally through all thicknesses of elastomer and at all the free stream velocities at which the experiments are performed.

The wall pressure signature of transonic shock/boundary layer interaction

2011 ◽  
Vol 671 ◽  
pp. 288-312 ◽  
Author(s):  
MATTEO BERNARDINI ◽  
SERGIO PIROZZOLI ◽  
FRANCESCO GRASSO
Keyword(s):  
Boundary Layer ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Space Time ◽  
Wall Pressure ◽  
Spanwise Direction ◽  
Frequency Spectra ◽  
Wall Pressure Fluctuations ◽  
Time Correlations

The structure of wall pressure fluctuations beneath a turbulent boundary layer interacting with a normal shock wave at Mach number M∞ = 1.3 is studied exploiting a direct numerical simulation database. Upstream of the interaction, in the zero-pressure-gradient region, pressure statistics compare well with canonical low-speed boundary layers in terms of fluctuation intensities, space–time correlations, convection velocities and frequency spectra. Across the interaction zone, the root-mean-square wall pressure fluctuations attain very large values (in excess of 162 dB), with a maximum increase of about 7 dB from the upstream level. The two-point wall pressure correlations become more elongated in the spanwise direction, indicating an increase of the pressure-integral length scales, and the convection velocities (determined from space–time correlations) are reduced. The interaction qualitatively modifies the shape of the frequency spectra, causing enhancement of the low-frequency Fourier modes and inhibition of the higher ones. In the recovery region past the interaction, the pressure spectra collapse very accurately when scaled with either the free-stream dynamic pressure or the maximum Reynolds shear stress, and exhibit distinct power-law regions with exponent −7/3 at intermediate frequencies and −5 at high frequencies. An analysis of the pressure sources in the Lighthill's equation for the instantaneous pressure has been performed to understand their contributions to the wall pressure signature. Upstream of the interaction the sources are mainly located in the proximity of the wall, whereas past the shock, important contributions to low-frequency pressure fluctuations are associated with long-lived eddies developing far from the wall.

Effects of Surface Irregularity on Turbulent Boundary Layer Wall Pressure Fluctuations

1984 ◽  
Vol 106 (3) ◽  
pp. 343-350 ◽  
Author(s):  
T. M. Farabee ◽  
M. J. Casarella
Keyword(s):  
Spectral Density ◽  
Flat Plate ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Velocity Profiles ◽  
Wall Pressure ◽  
Surface Irregularity ◽  
Wall Pressure Fluctuations ◽  
Frequency Components

Measurements were made of the mean velocity profiles and wall pressure field upstream and downstream of the flow over both a backward-facing and forward-facing step. For each configuration the velocity profiles show that the effects of the separation-reattachment process persist more than 24 step heights downstream of the step. Extremely high values of the RMS wall pressure are measured near reattachment. These values are 5 and 10 times larger than on a smooth flat plate for the backward-facing step and the forward-facing step, respectively. The spectral density of the wall pressure fluctuations in the recirculation region is dominated by low frequency components. Downstream of reattachment there is a reduction in the low frequency content of the wall pressures and an increase in the high frequency components. At the farthest measured position downstream, the spectral density is still higher than that found on a smooth flat plate. These results show that the complex turbulent flow generated by a surface irregularity can significantly increase the localized wall pressure field and these increases persist far downstream of the irregularity. Consequently, a surface irregularity can be a major source of turbulence-induced vibrations and flow noise, as well as a cause of the inception of cavitation in marine applications.

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