Internal versus External Flow
A fluid flow is classified as being internal or external, depending on whether
the fluid flows in a confined space or over a surface. The flow of an
unbounded fluid over a surface such as a plate, a wire, or a pipe is external
flow. The flow in a pipe or duct is internal flow if the fluid is completely
bounded by solid surfaces. Water flow in a pipe, for example, is internal flow,
and airflow over a ball or over an exposed pipe during a windy day is external
flow (Fig. 1–18). The flow of liquids in a duct is called open-channel flow if
the duct is only partially filled with the liquid and there is a free surface. The
flows of water in rivers and irrigation ditches are examples of such flows.
Internal flows are dominated by the influence of viscosity throughout the
flow field. In external flows the viscous effects are limited to boundary layers near solid surfaces and to wake regions downstream of bodies.
Comments
Post a Comment