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 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.

scholarly journals Influence of Surface Roughness Geometry on Trailing Edge Wall Pressure Fluctuations and Noise

2021 ◽  
Author(s):  
Fernanda Leticia dos Santos ◽  
Nikolaj A. Even ◽  
Laura Botero ◽  
Cornelius Venner ◽  
Leandro D. de Santana
Keyword(s):  
Surface Roughness ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Trailing Edge ◽  
Wall Pressure Fluctuations

LES Prediction of Wall-Pressure Fluctuations and Noise of a Low-Speed Airfoil

2009 ◽  
Vol 8 (3) ◽  
pp. 177-197 ◽  
Author(s):  
Meng Wang ◽  
Stephane Moreau ◽  
Gianluca Iaccarino ◽  
Michel Roger
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Transition To Turbulence ◽  
Trailing Edge ◽  
Frequency Spectra ◽  
Potential Core ◽  
Low Speed ◽  
Wall Pressure Fluctuations

This paper discusses the prediction of wall-pressure fluctuations and noise of a low-speed flow past a thin cambered airfoil using large-eddy simulation (LES). The results are compared with experimental measurements made in an open-jet anechoic wind-tunnel at Ecole Centrale de Lyon. To account for the effect of the jet on airfoil loading, a Reynolds-averaged Navier-Stokes calculation is first conducted in the full wind-tunnel configuration, and the mean velocities from this calculation are used to define the boundary conditions for the LES in a smaller domain within the potential core of the jet. The LES flow field is characterized by an attached laminar boundary layer on the pressure side of the airfoil and a transitional and turbulent boundary layer on the suction side, in agreement with experimental observations. An analysis of the unsteady surface pressure field shows reasonable agreement with the experiment in terms of frequency spectra and spanwise coherence in the trailing-edge region. In the nose region, characterized by unsteady separation and transition to turbulence, the wall-pressure fluctuations are highly sensitive to small perturbations and thus diffcult to predict or measure with certainty. The LES, in combination with the Ffowcs Williams and Hall solution to the Lighthill equation, also predicts well the radiated trailing-edge noise. A finite-chord correction is derived and applied to the noise prediction, which is shown to improve the overall agreement with the experimental sound spectrum.

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.

Measurements of the fluctuating pressure at the wall beneath a thick turbulent boundary layer

1962 ◽  
Vol 14 (2) ◽  
pp. 187-210 ◽  
Author(s):  
W. W. Willmarth ◽  
C. E. Wooldridge
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Pressure Fluctuations ◽  
Spatial Separation ◽  
Wall Pressure ◽  
Small Scale ◽  
Mean Square ◽  
Pressure Transducers ◽  
Wall Pressure Fluctuations ◽  
Displacement Thickness

Measurements of the turbulent pressure field at the wall beneath a thick (5-inch) turbulent boundary layer produced by natural transition on a smooth surface are reported. The data include the mean-square pressure, parallel to the stream, and spatial correlation of the pressure transverse to the stream.The root-mean-square wall pressure was 2.19 times the wall shear stress. The power spectra of the pressure were found to scale with the free-stream speed and the boundary-layer displacement thickness. A few tests with a rough surface showed that the increase in root-mean-square wall pressure was greater than the increase in wall shear stress.The space-time correlation measurements parallel to the stream direction exhibit maxima at certain time delays corresponding to the convection of pressure-producing eddies at speeds varying from 0.56 to 0.83 times the stream speed. The lower convection speeds are measured when the spatial separation of the pressure transducers is small, or when only the pressure fluctuations at high frequencies are correlated. Higher convection speeds are observed when the spatial separation of the pressure transducers is large, or when only low frequencies are correlated. The result that low-frequency pressure fluctuations have the highest convection speed is in agreement with the measurements of Corcos (1959, 1962) in a fully turbulent tube flow. Analysis of these measurements also shows that both large- and small-scale pressure-producing eddies decay after travelling a distance proportional to their scale. More precisely, a pressure-producing eddy of large or small wavelength λ decays and vanishes after travelling a distance of approximately 6λ.The transverse spatial correlation of the wall-pressure fluctuations was measured and compared with the longitudinal scale. Both the transverse and the longitudinal scale of the pressure fluctuations were of the order of the boundary-layer displacement thickness. The transverse and longitudinal scales of both large- and small-scale wall-pressure fluctuations were also measured and were also found to be approximately the same.

Prediction of the Blade Trailing-Edge Noise of an Axial Flow Fan

2011 ◽  
Author(s):  
Alain Guedel ◽  
Mirela Robitu ◽  
Nicolas Descharmes ◽  
Didier Amor ◽  
Je´rome Guillard
Keyword(s):  
Input Data ◽  
Pressure Fluctuations ◽  
Axial Flow ◽  
Suction Side ◽  
Axial Fan ◽  
Trailing Edge ◽  
Frequency Spectra ◽  
Pressure Transducers ◽  
Trailing Edge Noise ◽  
Wall Pressure Fluctuations

The objective of this work is to predict the trailing-edge noise of axial fans with an analytical model deduced from an extension of Amiet’s formulation. The input data of the acoustic model are the frequency spectra and the spanwise correlation length scales of the wall-pressure fluctuations on the blade suction side close to the trailing edge. This model was successfully validated in former studies on single steady airfoils in anechoic wind tunnels and, to a lesser extent, on an axial fan equipped with small unsteady pressure transducers flush mounted on the blade suction side. The present research is carried out on a 6-blade axial fan no longer equipped with embedded pressure transducers. The input data of the prediction are then deduced from non-dimensional spectra and correlation lengths of the pressure fluctuations measured in the previous study and RANS simulations performed on the test fan. A validation of the prediction method is made by comparing the predicted and measured sound power spectra of the fan for two blade pitch angles and different operating points.

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