The effect of a central jet on the base pressure of a cylindrical after-body in a supersonic stream

Abstract

This Report describes an experimental investigation of the factors affecting the base flow and jet structure behind a cylindrical after-body with a central nozzle. Seven interchangeable nozzles were tested. Six of these were convergent-divergent, with a design Mach number of 2.0, jet/base diameter ratios ranging from 0.2 to 0.8 and nozzle divergence angles ranging from 0 deg to 10 deg. The seventh nozzle was convergent with a jet/base diameter ratio of 0.6. In the main experimental programme the free-stream Mach number was 2.0 and the boundary layer was turbulent both on the after-body and in the nozzle. Measurements were made of the base pressure, the surface pressure distribution inside the nozzle, the overall thrust and the nozzle mass flow, over a range of jet pressures. This programme was supplemented by comparative tests with the jet exhausting into still air (static tests). Readings were taken of the internal nozzle pressures arm the jet thrust at different jet pressures. Schlieren photography was used extensively throughout. The results of the tests with external flow are presented in the form of curves showing the separate effects of jet pressure ratio, jet/base diameter ratio, nozzle design Mach number and nozzle divergence angle on the base pressure and overall thrust. The special case of base bleed is discussed separately. Similar curves are included for the static tests. These show the effect of jet pressure ratio-and nozzle geometry on the jet thrust. A general method of correlating data on annular base pressures is proposed and discussed. Essentially, this method compares the pressure on an annular base with the calculated pressure on the corresponding two-dimensional base. It correlates the present results reasonably well, but is less successful when applied to more extensive data.