Point-vortex simulations reveal universality class in growth of 2D turbulent mixing layers

Abstract

A central but controversial issue in free turbulent shear flows has been the universality (or otherwise) of their growth rates. We resolve this issue here in the special case of a temporal 2D mixing layer in a point vortex gas by extensive high-precision numerical simulations, utilizing for the first time a powerful ensemble-averaging strategy. The simulations show that the momentum thickness of such a mixing layer grows at the universal asymptotic rate of 0.0167 0.00017 times the velocity differential across the layer over a wide range of initial conditions, often after very long transients.