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Investigation of Turbulent Flow Noise Based on TR-PIV Data

Author: DiShuCheng
Tutor: ZhaoFeng
School: China Ship Research Institute
Course: Fluid Mechanics
Keywords: cavity flow flow noise TR-PIV Curle equation instantaneous pressure field
CLC: O357.5
Type: Master's thesis
Year: 2011
Downloads: 92
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Abstract


Either measuring or simulating is still difficult to predict the performance of flow noise. It is well accepted that the connection between flow and noise is the key to solve the problem. The Curle’s acoustic analogy presents an applicable approach to get the noise from the flow. To realize this, detailed flow information should first be accessible in spatio-temporal high resolution. Fortunately, the TR-PIV may pretty capture the instantaneous evolvement of a spatial flow field. Basing on the thought, a new attempt was set to find the corresponding relationship between the flow and its noise and predict the acoustic radiation from the flow data measured by TR-PIV.First, basing on particularly review of the updated references on the flow noise and detailed flow measurements by TR-PIV, the whole study route of the dissertation was set. A two-dimensional rectangular cavity with 3:1 aspect ratio was designed for the model test of TR-PIV. The TR-PIV measurement test was implemented in the cavitation tunnel of CSSRC. From the TR-PIV data, the time-averaged velocity, vorticity and turbulence intensity in and around the cavity were gotten and analyzed at different inflow speed. Besides these basic information of the flow field, the spectrum analysis was specially carried out for the inner cavity flow field by TR-PIV temporal measurements. By quantificational comparison, the overall feature and especially the peak of the frequency spectrum were in good agreement with the data of Rossiter empirical formula. The works showed that the TR-PIV measurement well captured the detailed flow characteristics of the cavity which would be helpful for understanding the complicated physical mechanism of the flow and building the bridge between the flow and its noise.Second, the corresponding pressure field is the internuncial necessity to predict the flow noise. To present a high fidelity instantaneous pressure field, the numerical integration method derived by incompressible Navier-Stokes momentum equations was adopted to solve the pressure distribution. An averaged method was used to evaluate and minimize the influence of different routes. The computer program of pressure integration was developed and validated by a synthetic rotational flow. Before applying the integration method to the real data by TR-PIV, the measured velocities were first processed by a numerical lowpass filter.This pre-process was remarkable for the following step to get the instantaneous pressures of high quality to predict flow noise.Finally, the Curle acoustic analogy was applied to numerically predict the acoustic radiation. The acoustic spectrums of the cavity at different receiving points were predicted and compared with the frequencies of vortex shedding in detail. It can be found that there is a certain quantitative relation between the acoustic radiation and the vortex shedding near the free shear layer of the cavity flow.

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CLC: > Mathematical sciences and chemical > Mechanics > Fluid Mechanics > Viscous fluid > Turbulence ( turbulence )
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