ABSTRACT
Many of the compressible flows that occur in engineering practice can be adequately modeled as a flow through a duct or streamtube whose cross-sectional area is changing relatively slowly in the flow direction. A duct is here taken to mean a solid-walled channel, whereas a streamtube is defined by considering a closed curve drawn in a fluid flow. A series of streamlines will pass through this curve as shown in Figure 2.1. Further downstream, these streamlines can be joined by another curve as shown in Figure 2.1.
