Chapter 3 - Boundary-Layer Equations

Abstract

This chapter considers the layer of fluid called the boundary layer in the narrow boundary region, where the velocity gradient may be so large that, even if the fluid viscosity is small, the viscous forces may be of the same order as the inertia forces. There, because gradients perpendicular to the surface are much larger than gradients parallel to the surface, some of the terms in the Navier-Stokes equations can be ignored, which simplifies the equations considerably. Boundary-layer approximations for compressible laminar and turbulent flows are discussed; then continuity, momentum, and energy equations are considered in relation to two-dimensional, three-dimensional and axisymmetric flows. Following this mean-kinetic-energy flows and Reynolds-stress transport equations are dealt with and the chapter concludes with an examination of integral equations of the boundary layer, including momentum, mean energy and turbulent energy integral equations.