A Study of the Influence of Air Release on Column Separation in an Aviation Kerosine Pipeline

Abstract

The occurrence of column separation on the downstream side of a valve in an aviation kerosine pipeline has been the subject of an investigation involving the method of characteristics to solve the partial differential equations governing the propagation of pressure transients. Particular attention has been paid to assessing the influence of air released from the fuel during the opening phase of the cavity and the cavity boundary equations have been modified accordingly. A series of experiments carried out on a test rig, utilizing L56 alloy fuel piping and other aircraft standard components and pumping aviation kerosine Specification 2494, has been employed to test the validity of the computing procedures developed. Comparison of the computed and observed results shows that the effect of released air is significant, but that it can be dealt with by including the partial pressure of any gas in the cavity in the equations governing cavity pressure and interface velocity. A wide range of tests indicate that the agreement between observed and predicted results for maximum and minimum pressures and event times following valve closure is at worst within 10 per cent. The predicted cavity collapse pressures are consistently above those observed. The velocity of the separated fuel column was measured, by means of a high speed camera, at 1000 frames/s and by a hot film probe and linearizer unit. The latter method proved successful, and should allow further work to be carried out on the measurement of velocity profiles during transient propagation.