A Parametric Study of Active Flow Control on a Rectangular Multi-Stream Supersonic Jet Nozzle*

Active control techniques are applied to a multi-stream rectangular supersonic nozzle. The nozzles unique geometry and operating conditions produce a highly three-dimensional turbulent field comprised of several canonical flows such as shear layers, shock-shear interactions, and supersonic mixing layers. The flow features a core (M = 1.6) flow that coalesces with a bypass (M = 1.0) stream behind a splitter plate and exits onto a deck plate on one side meant to simulate airframe integration. This interaction results in the emission of a high frequency tone that propagates throughout the flow field. Alleviation of this tone, as well as the near-field unsteadiness in the aft-deck region, and modification of the shock train are the areas sought to be addressed by the active control techniques. Active control to the system is implemented via steady blowing in the near-splitter plate region through an array of span-wise microjets. Several microjet configurations are tested experimentally varying the hole size, spacing, angle, and injection location. All the experiments were conducted within an anechoic chamber, providing the acquisition of simultaneous and synchronized pressure measurements in the far-field (via an array of microphones), in the near-field (via pressure transducers embedded within the aft deck plate), and time-resolved schlieren imaging at two downstream locations (providing measurements up to 3.5 diameters downstream). Spectral-Proper Orthogonal Decomposition techniques are applied to the schlieren image sets to quantify the spatio-temporal evolution of coherent structures for the different control configurations. This parametric study of active control configurations seeks to progress towards optimal control and understanding of the system as part of an extensive experimental (Syracuse University) and simulated (via LES at The Ohio State University) campaign.