LAUSR

Abstract Vorticity dynamics plays an essential role in the description of turbulent flows, so an alternative definition of the mixing length ( l ω = y H − y L , where y H and y L represent the transverse boundary positions of turbulent shear layer at the high- and low-speed free streams, respectively) in a turbulent planar mixing layer, based on the shear induced vorticity field, is suggested in this study. A theoretical analysis for determining the values of y H and y L in the self-preserving development region is presented. An experimental study that demonstrates the self-preserving state in planar turbulent mixing layer is next made with particle image velocimetry (PIV) measurements to support the theoretical results. It is shown that “a linear growth rate of l ω along stream-wise distance” can be now used as the necessary and sufficient conditions to identify the achievement of a self-preserving state in a turbulent mixing layer. Another advantage of this alternative definition of mixing length is that l ω gives a better sectional range of shear turbulence in a turbulent mixing layer than the usual definitions of mixing length, which are determined on the basis of the mean velocity field, such as l u .