An experimental investigation has been carried out to study themixing promoting efficiency of perforated tabs with 9.55% blokage (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. TheMach numberdecay along the centerline in case of subsonic and sonic jets and Pitotpressure decay in case of underexpanded jet (NPR3 and NPR4) were measured. Similarly Mach and Pitot pressure profiles along and normal to the tabs werealsomeasured Thewavespresentinthecoreofuncontrolledandcontrolled jets were visualized with shadowgraph technique. The nozzlepressurratio for shadowgraph was3, 4 and6. Theresults ofpreset studydemonstrate the validity of the hypothesis that, solid tab is better mixing promotr among all the tabs investigated in the subsonic and sonic jets. Thrust loss associated with moreblockagesincase ofsolidtab can beregardedasmajor disadvanage, which is overcome by perforated tabs used in presentstudy. Tab with 2 mm circular perforation due to varying sizes of vortices shed by the combination of perforation and webith varying width of webfrom center to tangential web is better mixing promoter than other the tabswith 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 mmcircular perforation are 47.61%.
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