Small Silicon Pressure Transducers for the Determination of the Longitudinal Space-Time Correlation of Wall Pressure Fluctuations

1995 ◽  
pp. 335-339
Author(s):  
L. Löfdahl ◽  
E. Kälvesten ◽  
G. Stemme
Keyword(s):  
Pressure Fluctuations ◽  
Time Correlation ◽  
Space Time ◽  
Wall Pressure ◽  
Pressure Transducers ◽  
Wall Pressure Fluctuations

Wall-pressure fluctuations beneath turbulent boundary layers on a flat plate and a cylinder

1970 ◽  
Vol 41 (1) ◽  
pp. 47-80 ◽  
Author(s):  
W. W. Willmarth ◽  
C. S. Yang
Keyword(s):  
Boundary Layer ◽  
Pressure Field ◽  
Time Correlation ◽  
Space Time ◽  
Wall Pressure ◽  
Plane Boundary ◽  
Wall Pressure Fluctuations ◽  
Turbulent Pressure ◽  
Transverse Scale ◽  
Convection Speed

Measurements of the turbulent pressure field on the outer surface of a 3 in. diameter cylinder aligned with the flow were made at a point approximately 24 ft. downstream of the origin of the turbulent boundary layer in an air stream of 145 ft./sec. The boundary-layer thickness was 2·78 in. and the Reynolds number based on momentum thickness was 2·62 × 104. The wall-pressure measurements were made with pressure transducers constructed from 0·06 in. diameter lead–zirconate–titanate disks mounted flush with the wall. The measurements including root-mean-square, power spectrum, and correlations of the wall pressure are compared with the existing experimental results for the turbulent pressure field beneath a plane boundary layer. The streamwise convection speed deduced from longitudinal space-time correlation measurements was almost identical to that obtained in the plane boundary layer. The rate of decay of the maxima of the space-time correlation of the pressure produced by the convected eddies was double that in a plane boundary layer. The longitudinal and transverse scales of the pressure correlation were approximately equal (in a plane boundary layer the transverse scale is larger than longitudinal scale) and were one-half or less than the longitudinal scale in the plane boundary layer. It is concluded that the effect of the transverse curvature of the wall is an overall reduction in size of pressure-producing eddies. The reduction in transverse scale of the larger eddies is greater than that of the smaller eddies. In general, the smaller eddies decay more rapidly and produce greater spectral densities at high frequencies owing to the unchanged convection speed.

Effect of Internal Bubbly Flow on Channel Vibration: Comparison Between Experiment and Model

2008 ◽  
Author(s):  
Ming Ming Zhang ◽  
Joseph Katz ◽  
Andrea Prosperetti
Keyword(s):  
Void Fraction ◽  
Channel Wall ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Pressure Fluctuations ◽  
Initial Energy ◽  
Wall Pressure ◽  
Attenuation Coefficients ◽  
Pressure Transducers ◽  
Wall Pressure Fluctuations

The effect of an internal turbulent bubbly flow on vibrations of a channel wall is investigated in this paper both experimentally and theoretically. Vibrations of an isolated channel wall and associated wall pressure fluctuations are measured using several accelerometers and pressure transducers along streamwise direction under various gas void fractions and characteristic bubble diameters. A waveguide theory based mathematical model, i.e. a solution to the 3D Helmholtz Equation in an infinite long channel, and the physical properties of bubbles is developed to predict the spectral frequencies of the vibration and the wall pressure fluctuation, the corresponding attenuation coefficients of spectral peak and propagated phase speeds. Results show that compared with the same flow without bubbles, the presence of bubbles substantially enhances the power spectral density of the channel wall vibrations and pressure wall fluctuations in the 250–1200 Hz by up to 27 dB and 26 dB, respectively, and increases their overall rms values by up to 14.1 times and 12.7 times, respectively. In the lower frequency range than the resonant frequency of individual bubble, i.e. 250–1200 Hz range, both vibrations and spectral frequencies increase substantially with increasing void fraction and slightly with increasing bubble diameter. The origin for enhanced vibrations and wall pressure fluctuations is demonstrated to be the excitation of the streamwise propagated acoustic pressure waves, which are created by the initial energy generated during bubble formations. The measured magnitudes and trends of the frequency of the spectral peaks, their attenuation coefficients and phase velocities are well predicated by the model. All the three variables decrease as the void fraction or bubble diameter increase. But the effect of void fraction is much stronger than that of bubble diameter. For the same void fraction and bubble diameter, the peaks at higher spectral frequencies decay faster.

Direct Determination of the Onset of Transition to Turbulence in Flow Passages

1991 ◽  
Vol 113 (4) ◽  
pp. 602-607 ◽  
Author(s):  
N. T. Obot ◽  
J. A. Jendrzejczyk ◽  
M. W. Wambsganss
Keyword(s):  
Reynolds Number ◽  
Pressure Fluctuations ◽  
Direct Determination ◽  
Wall Pressure ◽  
Transition To Turbulence ◽  
Pressure Data ◽  
Wall Pressure Fluctuations ◽  
Power Spectral ◽  
Critical Reynolds Numbers

Easily applied methods are proposed, based on tests with air and water, for direct determination of the onset of transition in flow passages using static and dynamic wall pressure data. With increasing Reynolds number from laminar flow, the characteristic feature of transition is the change from steady to oscillating pressure readings. It is established that the power spectral density (psd) representations exhibit a distinctive change in profile at transition. Further, it is shown that the root-mean-square (rms) values of the wall pressure fluctuations rise sharply at transition. The critical Reynolds numbers recorded via the change from steady to unsteady pressure readings are almost the same as those deduced from the psd and rms pressure data or from the familiar friction factor-Reynolds number plots.

scholarly journals Wall pressure fluctuations induced by a single stream jet over a semi-finite plate

2020 ◽  
Vol 19 (3-5) ◽  
pp. 240-253 ◽  
Author(s):  
Stefano Meloni ◽  
Jack LT Lawrence ◽  
Anderson R Proença ◽  
Rod H Self ◽  
Roberto Camussi
Keyword(s):  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Trailing Edge ◽  
Statistical Characterization ◽  
Pressure Transducers ◽  
Finite Plate ◽  
Wall Pressure Fluctuations ◽  
Time Domains ◽  
Subsonic Regime ◽  
The University

This work provides an experimental investigation into the interaction between a jet flow and a semi-finite plate parallel to the jet. Wall pressure fluctuations have been measured in a high compressible subsonic regime and for different distances between the jet and the plate trailing edge. The experiment has been carried out in the ISVR anechoic Doak Laboratory at the University of Southampton, using wall pressure transducers flush mounted on the plate surface. Signals were acquired in the stream-wise direction along the jet centreline and in the span-wise direction in a region close to the trailing edge. The radial position of the flat plate was fixed very close to the jet axis to simulate a realistic jet–wing configuration. The plate was moved axially in order to investigate four different jet-trailing edge distances and to include measurements upstream of the nozzle exhaust. The acquired database was analyzed in both the frequency and the time domains providing an extensive statistical characterization in terms of spectral uni– and multi–variate quantities as well as high order statistical moments. A wavelet analysis was performed as well to investigate the time evolution of the wall pressure events.

Effect of Bubbles on Flow Induced Vibration

2006 ◽  
Author(s):  
Angela R. Pelletier ◽  
Ian A. McKelvey ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Bubble Size ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Flow Induced Vibration ◽  
Pressure Transducers ◽  
Plate Vibrations ◽  
Wall Pressure Fluctuations ◽  
Bubble Sizes ◽  
The Impact

The effects of a turbulent, bubbly boundary layer on wall skin friction have been investigated in numerous previous studies. However, the impact of such a multiphase flow on fluid-structure interactions has not been studied. To this end, the present project examines experimentally the effect of a bubbly boundary layer on the vibration of a vertical plate. Using a combination of accelerometers and pressure transducers, we simultaneously measure the plate vibrations and wall pressure fluctuations for varying flow rates, gas void fractions, and characteristic bubble sizes. The results show that the presence of bubbles substantially increases both the plate vibrations and the wall pressure fluctuations. The vibrations increase by up to 20 dB compared to the same flow without bubbles. The spectra of vibrations become broad and vary significantly with the characteristic bubble size. The variations with bubble size are consistent with the resonant frequency of the bubbles, indicating that, in addition to changing the compressibility of the medium, individual bubbles act at sources.

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.

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