The influence of phase-averaging window size on the determination of turbulence quantities in unsteady turbulent flows |
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Authors: | Z Zhang K Eisele F Hirt |
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Institution: | (1) Fluid Dynamics Laboratory 1504, Sulzer Inotec, CH-8401 Winterthur, Switzerland, CH |
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Abstract: | The phase-averaging window size is shown to affect the measurement of phase-averaged turbulence quantities in unsteady turbulent
flows. The flow turbulence is usually estimated on the assumption of quasi-constant flow velocity during the duration of the
phase-averaging window. The calculated turbulence level then consists of two parts: one due to the turbulent velocity fluctuations
and the other due to the changes in the mean flow velocity. This second part is shown to be directly proportional to the averaging
window size. In order to determine the true turbulence the averaging window size has to be made as small as possible, especially
if the unsteady flow exhibits large temporal gradients and the flow turbulence itself is small.
Received: 9 April 1996/Acceped: 17 August 1996 |
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