Two-dimensional shear-layer entrainment

It is observed experimentally that a spatially growing shear layer entrains an unequal amount of fluid from each of the freestreams, resulting in a mixed fluid composition that favors the high-speed fluid. A simple argument is proposed, based on the geometrical properties of the large-scale now structures of the subsonic, fully developed, two-dimensional mixing layer, which yields the entrainment ratio and growth of the turbulent mixing layer. The predictions depend on the velocity and density ratio across the layer and are in good agreement with measurements to date.