ABSTRACT
In the application of the governing equations, although in some flow cases, one may ignore (or not need to model) the flow resistance, in most practical flow cases in general, one must account for the fluid viscosity and thus model the resulting shear stress and flow resistance. As such, in the application of the governing equations (continuity, energy, and momentum), it is important to make the distinction between real flow, ideal flow, and a hydraulic jump. And, for ideal flow, it is important to make the distinction between internal flow (pipe or open channel flow), external flow, and flow from a tank (see Table 4.1). While the continuity, energy, and momentum equations are applied (as necessary) to internal flows (pipe and open channel flow) and to flow from a tank, etc., only the energy and momentum equations are applied to external flows. The application of the governing equations (continuity, energy, and momentum) for real flow (internal) and ideal flow (flow-measuring devices for internal flow, and external flow around objects) requires the modeling of flow resistance (frictional losses). The modeling of flow resistance requires a “subset level” application of the governing equations. However, in the application of the governing equations (continuity, energy, and momentum) for ideal flow (flow from a tank, etc., and gradual channel transitions) and a hydraulic jump, there is no flow resistance to model. While in the case of ideal flow (flow from a tank, etc., and gradual channel transitions), the flow resistance is actually ignored, in the case of the hydraulic jump, the major head loss is due to flow turbulence due to the jump and not due to flow resistance (frictional losses).
