Decay of Turbulence in a Closed Vessel : 4th Report, Comparison between the Results of Theoretical Calculations and the Experimental Ones

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The authors carried out the numerical integrations with several initial shapes of spectra and with varied initial values of Reλ according to the Kraichnan theory which was introduced in order to complete the series of equations expressing decay of turbulence in free space. By comparing the results of calculation with the experimental results obtained for the decay of grid-turbulence in a steady tunnel flow carried out by Van Atta et al., it was first proved that the validity of Kraichnan theoty was satisfactory. It was found that the asymptotic line of the decay-law of turbulence resulting from the theoretical computations was able to be approximated by the line of decay-law experimentally obtained by the authors for the relaxed turbulence in closed vessel. It was also found that (1) depending on whether the peak in the initial spectrum was too high or too low, the approaching manner toward the asymptote was reversed, and the influence of the manner on the time variation of turbulence characteristics was significant ; and (2) there existed the most conformable form of spectrum for a turbulence field with respect to the existing turbulence intensity and viscosity, and the peak of the spectrum grew steeper as decay of turbulence progressed.
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