Comparisons between different approximations to energy dissipation rate in a self-preserving far wake

By using a four-hot-wire probe and an eight-hot-wire probe, different approximations to energy dissipation rate have been made in the far field of a cylinder wake. The appropriateness of the various approximations is evaluated by examining their mean values, spectra, conditional analysis, and scaling range exponents. It is found that there are significant differences between the instantaneous values of epsilon(iso), the isotropic dissipation rate, and other approximations. The present measurements also allow the examination of the spatial correlation between the energy dissipation rate and the enstrophy Omega. While the correlation between epsilon(iso) and Omega is low, there is a strong correlation between the other approximations to energy dissipation rate epsilon and the enstrophy Omega. The scaling range exponents show that the substitutes to the energy dissipation rate and enstrophy based on isotropy are more intermittent than their corresponding true values. The present results suggest that using epsilon(iso) as a substitute of epsilon should be re-examined, especially for the instantaneous values.