Innovative passive control for high speed jets

Abstract

newlineAn experimental investigation has been carried out to study the mixing promoting efficiency of perforated tabs with 9 55 blockage solid tab 8 42 blockage 1 5 mm circular perforation 7 55 blockage 2 mm circular perforation and 6 42 blockage 2 5 mm circular perforation Tabs were attached diametrically opposite at the convergent nozzle The investigation was carried out for the jet with the exit Mach 0 2 0 4 0 6 0 8 1 0 and sonic underexpanded levels of NPR3 and NPR4 The Mach number decay along the centerline in case of subsonic and sonic jets and Pitot pressure decay in case of underexpanded jet NPR3 and NPR4 were measured Similarly Mach and Pitot pressure profiles along and normal to the tabs were also measured The waves present in the core of uncontrolled and controlled jets were visualized with shadowgraph technique The nozzle pressure ratio for shadowgraph was 3 4 and 6 The results of present study demonstrate the validity of the hypothesis that solid tab is better mixing promoter among all the tabs investigated in the subsonic and sonic jets Thrust loss associated with more blockages in case of solid tab can be regarded as major disadvantage which is overcome by perforated tabs used in present study Tab with 2 mm circular perforation due to varying sizes of vortices shed by the combination of perforation and web with varying width of web from center to tangential web is better mixing promoter than other the tabs with 1 5 mm 2 5 mm circular perforation As high as 61 9 reduction in core length was achieved with 2 mm circular perforation at 0 6 jet Mach number The corresponding core length reduction caused by 1 5 mm and 2 5 mm circular perforation are 47 61 newline newline