Comparison of Unsteady Flow Discharge Coefficients for Sharp-Edged Orifices with Steady Flow Values

Abstract

A simple theory, based on quasi-steady, one-dimensional flow arguments, is presented for the reflection of a compressive wave in air in a pipe when incident upon a coaxial, convergent nozzle situated at the end of the pipe. Preliminary shock-tube experiments using quadrant arc nozzles confirm the validity of the theory, and thus enable it to be used to predict the discharge coefficients of sharp-edged orifices from pressure measurements taken in the pipe in the immediate vicinity of the orifices during further shock-tube experiments. Steady flow discharge coefficients measured experimentally differ from the unsteady flow values by a maximum of 7 per cent.