Boundedness of the velocity derivative skewness in various turbulent flows

The variation of S. the velocity derivative skewness, with the Taylor microscale Reynolds number Re-lambda is examined for different turbulent flows by considering the locally isotropic form of the transport equation for the mean energy dissipation rate (epsilon) over bar (iso). In each flow, the equation can be expressed in the form S +2G/Re-lambda= CIRe lambda, where G is a non-dimensional rate of destruction of (epsilon) over bar (iso) and C is a flow-dependent constant. Since 2G/Re-lambda is found to he very nearly constant for Re-lambda >= 70, S should approach a universal constant when Re-lambda is sufficiently large, but the way this constant is approached is flow dependent. For example, the approach is slow in grid turbulence and rapid along the axis of a round jet. For all the flows considered, the approach is reasonably well supported by experimental and numerical data. The constancy of S at large Re A has obvious ramifications for small-scale turbulence research since it violates the modified similarity hypothesis introduced by Kolmogorov (J. Fluid Mech., vol. 13, 1962, pp. 82-85) but is consistent with the original similarity hypothesis (Kolmogorov, Doki. Akad, Nauk SSSR, vol. 30, 1941, pp. 299-303).