Active Flow Control in a Supersonic Rectangular Jet

This paper summarizes the results of high-speed schlieren experiments on a supersonic rectangular jet of sharp throated design. The rectangular nozzle is of aspect ratio two and has a design Mach number of 1.50. A strongly screeching overexpanded case as well as the weakly screeching nozzle design case are investigated. LAFPA based excitation is used to explore the inherent physics of the jet as well as to control the generation and development of coherent structures (CS). The baseline jet displays a screech signature with a natural flapping mode behavior. LAFPA excitation at the screech frequency is able to reinforce the natural behavior or shift some energy towards another azimuthal pattern, depending on the excitation mode employed. Exciting the jet at a frequency above the natural screech produces smaller CS in an azimuthal mode reflecting that of the excitation. The smaller structures entrain less ambient air resulting in thinner shear layers and a lengthened jet core. The excitation is able to disrupt the natural screech loop when the jet is screeching weakly (operated at the design condition), resulting in the LAFPA introduced structures dominating the flow.