Effect of Injector Shape on Penetration and Spread of Liquid Jets

Abstract

L injection into a supersonic air stream finds applications in supersonic combustion ramjets (scramjets), transpiration cooling of re-entry bodies and thrust vector control of rockets. The injector geometry will have a significant role in liquid injection applications. The injection of liquid into a supersonic air stream produces an interaction shock and a freestream boundary-layer separation zone upstream of the injector. The separation zone plays an important role during combustion due to the high rate of heat transfer to the wall in this region. The shock system associated with each injector in a practical supersonic combustor has two important effects: 1) it reduces the total pressure of the freestream and thus adversely affects the overall performance of the engine; 2) static temperature and pressure of the freestream rise through the injector shock system thus creating better conditions from the viewpoint of chemical reaction rates. The shape and strength of the shock also affect the forces on the liquid column and thus penetration. In general, the shock system is a strong function of injector geometry. The influence of injector geometry on penetration and spread of the jet were given major emphasis in the present investigation. The purpose was to obtain experimental penetration and spread data suitable for engineering use and to seek theoretical correlations incorporating and governing parameters. The motivation for the present work comes from the work of Kush and Schetz who observed that a liquid jet through a rectangular slot aligned with the flow gives significantly higher penetration than through a circular hole of the same area.