Noise Filtering for Wall-Pressure Fluctuations in Measurements Around a Cylinder With Laminar and Turbulent Flow Separation

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
C. Sardu ◽  
D. Lasagna ◽  
G. Iuso
Keyword(s):  
Turbulent Flow ◽  
Flow Separation ◽  
Adaptive Filters ◽  
Fluid Dynamic ◽  
Pressure Fluctuations ◽  
Free Field ◽  
Noise Cancellation ◽  
Wall Pressure ◽  
Wall Pressure Fluctuations ◽  
Laminar And Turbulent Flow

This paper proposes two different noise cancellation techniques for cleaning wall-pressure fluctuations signals. These fluctuations are measured around a circular cylinder with laminar and turbulent flow separation. The noise cancellation techniques are based on Wiener and adaptive filters and use the signals of pressure transducers mounted in a cross section of the cylinder and the signal of a free-field sensor opportunely located upstream. First, synthetic signals are used in order to validate the procedure. Then, both techniques are applied to the experimental data. Specific attention is paid to the filter order, optimized by a method introduced in this paper. Both filter types showed a selective behavior preserving the essence of the fluid dynamic phenomena characterizing the flow fields at each Reynolds number tested, especially when laminar separation occurs.

Improvement on acoustic performance of the accumulator of double-cylinder rotary compressors

2007 ◽  
Vol 221 (11) ◽  
pp. 1391-1396 ◽  
Author(s):  
Z Y Huang ◽  
W K Jiang ◽  
C H Liu ◽  
H S Jin ◽  
Y Zhou
Keyword(s):  
Noise Level ◽  
Fluid Dynamic ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Rotary Compressor ◽  
Acoustic Performance ◽  
Wall Pressure Fluctuations ◽  
Large Pressure ◽  
Flow Phase ◽  
Single Pipe

Since the accumulator is one of main contributors to the overall noise level of the rotary compressor, research on the acoustic performance of accumulators is essential. Numerical analysis based on the computational fluid dynamic method shows that large pressure fluctuations are caused mainly by periodic rotating piston. The idea that the flow phase differences of two pipes could be utilized for suppressing fluctuations is proposed. The double standpipes of an accumulator are changed to the single pipe with two branches and each branch is connected to the inlet of the compressor. Flow structures and wall pressure fluctuations for the two configurations are computed. Computational results show that wall pressure pulsations of the new accumulator are obviously lower than that of the original. The acoustic experiments were carried out under the real working conditions. Compared with the original, the new accumulator shows that the overall noise level is reduced about 1.2 dB(A) and the sound spectrum levels are also lower in a wide frequency domain, which validate the numerical and theoretical analysis.

Wall Pressure Fluctuations in the Reattachment Region of a Backward Facing Step

2007 ◽  
Author(s):  
Yu-Tai Lee ◽  
Theodore M. Farabee ◽  
William K. Blake
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Turbulent Kinetic Energy ◽  
Source Term ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Mean Flow ◽  
Backward Facing Step ◽  
Fluctuating Pressure ◽  
Wall Pressure Fluctuations

Steady mean flow fields and turbulent flow characteristics obtained from solving the Reynolds Averaged Navier Stokes (RANS) equations with a k-ε isotropic turbulence model are used to predict the frequency spectrum of wall-pressure fluctuations for flow past a backward facing step. The linear source term (LST) of the governing fluctuating-pressure equation is used in deriving the final double integration formula for the fluctuating wall pressure. The integrand of the solution formula includes the mean-flow velocity gradient, modeled turbulence normal fluctuation, Green’s function and the spectral model for the interplane correlation. An anisotropic distribution of the turbulent kinetic energy is implemented using a function named anisotropic factor. This function represents a ratio of the turbulent normal Reynolds stress to the turbulent kinetic energy and is developed based on an equilibrium turbulent flow or flows with zero streamwise pressure gradient. The spectral correlation model for predicting the wall-pressure fluctuations is obtained through modeling of the streamwise and spanwise wavenumber spectra. The nonlinear source term (NST) in the original fluctuating-pressure equation is considered following the conclusion of Kim’s direct numerical simulation (DNS) study of channel flow. Predictions of frequency spectra for the reattachment flow past a backward facing step (BFS) are investigated to verify the validity of the current modeling. Detailed turbulence features and wall-pressure spectra for the flow in the reattachment region of the BFS are predicted and discussed. DNS and experimental data for BFSs are used to develop and validate these calculations. The prediction results based on different modeling characteristics and flow physics agree with the observed turbulence field.

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.

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