Resolvent Analysis of a Supersonic Rectangular Multi-stream Jet Flow*

We perform a resolvent analysis of a supersonic multi-stream jet flow to understand its principal dynamics, with the ultimate goal of acquiring physical insights for flow control design. The nozzle configuration comprises three primary shear layers: (i) an upper shear layer between the flow on the upper single-sided expansion ramp stream and the freestream, (ii) a splitter plate shear layer from the mixing of a core Mach 1.6 stream and a sonic lower stream which evolves above an aft deck-plate and (iii) a lower shear layer downstream of the aft-deck plate where it mixes with the freestream flow. The time-averaged flow field obtained from an LES is used as the base flow to construct a resolvent operator. A range of frequency-spanwise wave number pairs is considered. For cases with large gains, the dominant response modes are observed in the lower shear layer region downstream of the aft deck-plate. In sub-dominant modes, the response is concentrated in the upper shear layer and the splitter-plate shear-layer regions. Furthermore, a discounted resolvent analysis is performed over a finite-time window by introducing a discount parameter in the resolvent operator. Observations from the resolvent analysis will imply active and passive flow control design and parameter selection.