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

Abstract

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.

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“…( 12) and ( 13) to retrieve parameters z 1 and z 2 . For the current study, we did not perturb our synthetic data by random noise because: (1) when generating time-averaged synthetic transmissivity data, the noise will be simply smoothed out when calculating the average; (2) although adding random noise to the instantaneous synthetic transmissivity data will significantly alter the rms synthetic transmissivity spectrum, techniques may be applied to filter random noise from turbulent signals [60,61] or distinguish uncorrelated measurement noise from correlated turbulent fluctuations [62]. However, this is beyond the scope of the current study.…”