Influence of perforated tabs on subsonic set control

An experimental analysis has been carried out to examine the mixing encouraging effectiveness of tabs with circular perforation of different perforation diameters, 1.5 mm, 2 mm and 2.5 mm. The geometrical blockage offered by the perforated tabs, placed diametrically opposite, at the nozzle exit, were 8.42%, 7.55% and 6.42%, respectively, for perforation diameters 1.5 mm, 2 mm and 2.5 mm. The Mach along the jet central axis and Mach profiles in the directions along and tangential to the tabs were calculated at various axial locations. The results of the Mach 0.4, 0.6 and 0.8 jets studied show that the tab with 2 mm perforation is a better mixing promoter than 1.5 mm and 2.5 mm perforations, effecting in a core length decrement of 62% for Mach 0.6 jet. The corresponding reduction in core length for 1.5 mm and 2.5 mm holes are only 47.61% and 42% respectively.