Non-Steady Flow through a Square-Edged Orifice in a Pipe

One-dimensional quasi-steady flow theories for flow through an orifice in a pipe are developed. These theories are presented in a form to be used with wave action calculations using the methods of characteristics. Steady flow experiments are described for determining the effective area of the orifice and the location of the plane of the pressure recovery. Non-steady flow tests using a single unit of a pulse generator are described. The results of non-steady flow experiments in the pipe are compared with the calculated pressure diagrams using a quasi-steady flow one-dimensional theory. These showed that the theory may be used for predicting the overall wave action in the pipe. In the plane of the enlargement, downstream of the orifice, the theory did not give an exact prediction of the pressure, particularly with small orifice area to pipe area ratios and high overall pressures. For small pressure changes, however, it is considered that the theory was satisfactory and may be used as the basis for calculating instantaneous mass flows if a square-edged orifice was used in pulsating flow streams.