DefinePK

Abstract

In this paper results reported are the outcome of investigation carried to regulate the suddenly expanded flow through a converging-diverging nozzle at high supersonic Mach numbers and at lower length to diameter ratios. The geometrical and the flow variables assessed in this investigation are the diameter ratio, length to diameter (L/D) ratio, expansion level, and the Mach number. The step heights of the present case are 1.6, 1.8, 2.2 and 2.5. The tests were conducted for P0/Patm in the range of 3 to 11. The (L/D) ratio of the suddenly expanded duct of the test was from 10 to 1, however, the outcome are presented for L/D 4, 3, 2, and 1. The Mach numbers tested in the investigation are 1.9, 2.1, 2.4, and 2.8. The results show that the efficacy of the active control is considerable in regulating the base pressure. Further, it found that for Mach numbers 1.9 and 2.1 the control is very effective for NPRs 9 and 11 but, for NPRs 3, 5, and 7 the control efficiency is only marginal. At NPRs 7 and 9 for some cases peculiar trends are observed and the flow becomes oscillatory. It is seen that majority of the outcomes represent similar behavior for duct length up to L = 3D, which means; that the back pressure has not negatively affected the flow field in the base region as well as in the duct. The lowest duct length needed for the flow to remain latched on with the duct is L/D = 3 in general for all the cases of the flow variables of the current investigation, however, for few combinations of the flow and geometrical parameters the flow remains attached even for L/D =2 as well as 1. With this it can be stated that the micro jets can be used as one of the methods for flow in the base area control without having any untoward effect in the flow field at the base region.