ABSTRACT
We have examined in some detail the effects of area changes on a compressible flow, and in doing so we have invoked the isentropic idealization. When it was impossible to obtain realistic results under the constraints of this idealization, such as in the case of the C-D nozzle with partially supersonic flow, a model was developed for entropy change by means of a discontinuity—the shock wave. In this chapter we look at other common cases in which entropy changes, but, as has been our habit, we remove one complication to make room for another. In this chapter, for the study of compressible flows with entropy change, we restrict our discussion to cases in which the flow cross-sectional area is constant. (Recall that in cases involving shock waves, the constant-area approximation was also appropriate.) When computer methods are brought into play, it is a relatively simple matter to relax the constant-area constraint and compute the effects of area change from the principles outlined in Chapter 7.
