Growth of the two-dimensional mixing layer from a turbulent and nonturbulent boundary layer

Abstract

The effect of the initial boundary layer upon the downstream growth of the turbulent mixing layer between two streams is studied experimentally. Two conditions are carefully documented; in one case the boundary layers at separation are laminar and in the other case one boundary layer is made turbulent with a trip wire. When the boundary layer is turbulent; the lateral length scale, ϑ, characterizing the thickness of the mixing region, grows more slowly. At 400–500 initial momentum thickness downstream, the growth rate relaxes toward, but does not meet, the growth rate of the untripped mixing layer. The lateral distributions of the turbulence quantities, when scaled with the local lateral thickness, achieve the same form at distances beyond approximately 800 initial momentum thicknesses.