The effects of base bleed on plug nozzles

Abstract

This is an experimental comparison Of two axi-symmetric, isentropic plug nozzles. In one of these (Model No. 1) the afterbody is cylindrical and a secondary flow is bled into the annular base. The other (Model No. 2) has a parabolic afterbody with no base or bleed. In both cases the expansion is all-external and the design pressure ratio is 14. These models were tested over a range of primary and secondary flows at M∞ = 0, 0.9 and 2.0. In the case of Model No. 1 measurements include the primary and secondary flow rates, the base pressure and the plug pressure distribution. The overall thrust was determined by a balance and analysed into its components; namely, the nozzle thrust and the drag of the bleed system. With Model No. 2 only the primary flow rate and overall thrust were measured. Both nozzles are efficient at the cruising condition (M∞ = 2.0) and both are exceptionally flexible with regard to off-design operation (M∞ = 0.9 and 0). However, at M∞ = 0.9 and 2.0, the overall thrust of Model No. 1 using optimum bleed is slightly less than that of Model No. 2.