7 - Short Cut Methods

Abstract

This chapter discusses simple methods and formulas for calculating two-dimensional turbulent flows. Their main advantage and usefulness lies in their simplicity; unlike differential boundary-layer and Navier-Stokes methods, they either do not require computers or require only small computers. They can be easily used in many practical engineering problems. For laminar flow over a flat plate, the boundary-layer parameters can be obtained exactly from the solution of the similarity equations and can be expressed in terms of very useful formulas. For a turbulent flow, the momentum and energy equations do not reduce to similarity equations. Furthermore, the presence of the Reynolds stress terms in the equations prevents an exact solution. The analysis of thermal boundary layers on smooth surfaces with specified heat flux is similar to those with specified temperature. The difference in Stanton-number formulas between the constant wall heat flux case and the constant wall temperature case is considerably more in laminar flows, where the difference is 36 percent.