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Confined Flows

Underlying Flow Regime 4-08


The flow through a sharp-edged orifice plate mounted concentric into a pipe of constant cross-section induces a flow contraction and a separation downstream of the orifice plate. The narrowest cross-section of the flow is however not located in the orifice itself, but some distance downstream (Figure 1). The region of the narrowest cross-section is often called “vena contracta”. Further downstream of this location the flow expands again up to the pipe cross-section. Naturally, such a flow configuration is associated with a considerable pressure loss, since a great deal of kinetic energy is dissipated within the recirculation region. Therefore, such an orifice plate is often used as a flow meter mounted into a pipe (Hayward 1979). For such an application normally a special design of the orifice hole is used and the pressure tapings should be mounted at a certain distance with respect to the orifice location (Figure 2).

Figure 1. Illustration of the flow structure through a pipe with a sharp-edge orifice plate.
Figure 2. Different designs of the orifice plates used for flow meters.

Contributors: Martin Sommerfeld - Martin-Luther-Universitat Halle-Wittenberg