Improved entrainment method for calculating turbulent boundary layer development

Abstract

Summary. A simple integral method is presented for the calculation of two-dimensional incompressible turbulent boundary layers. Use is made of established relationships to determine values of the entrainment coefficient for equilibrium layers, and the entrainment coefficient for non-equilibrium conditions is obtained by multiplying the corresponding equilibrium value by a suitable empirical function. This increases the entrainment when the rate of growth of the layer is less than that of the corresponding equilibrium layer, and decreases it when the rate of growth is greater. This variation of entrainment is in accordance with observation, and a simple physical explanation is proposed to account for it. This explanation further suggests how the effects of flow convergence may be taken into account. Comparisons with measured boundary-layer developments show the general accuracy of the method.