Corrugated Tabs for Supersonic Jet Control

The efficiency of corrugated tabs in promoting the mixing of Mach 1.8 axisymmetric jet has been investigated experimentally. Two rectangular tabs of 4.2% blockage, with corrugations at the edges, located diametrically opposite at the exit of a Mach 1.8 convergent-divergent nozzle were found to be better mixing promoters than identical rectangular tabs without corrugations, at overexpanded, correctly expanded, and underexpanded states of the jet. Furthermore, the corrugated tabs were found to be more efficient in weakening the shocks in jet core compared with the plain tabs. As high as 78 % of reduction in core length was achieved with corrugated tabs for the jet operated at nozzle pressure ratio of 7, the corresponding reduction with the plain tabs is only 54%. The mixing effectiveness of corrugated tabs increases progressively with increase of nozzle pressure ratio whereas, the maximum mixing effectiveness of the plain tabs is found to be at the correctly expanded state. The shadowgraph pictures for the uncontrolled and controlled jets clearly demonstrate the effectiveness of corrugated tabs in weakening the waves in the jet core. The speculation of smaller vortices generated by the corrugated tab is supported by a preliminary visualization with water flow channel.