Tri-global resolvent analysis of a supersonic multi-stream rectangular nozzle flow

We conduct a tri-global resolvent analysis of a supersonic multi-stream rectangular nozzle flow in a three-dimensional (3-D) domain with spanwise periodicity to understand the flow’s global perturbation dynamics. The configuration consists of three primary shear layers: (I) an upper shear layer (USL) forming due to the jet flow and the freestream on the upper side of the nozzle, (II) a splitter plate shear layer (SPSL) from the mixing of a core Mach 1.6 stream and a bypass Mach 1.0 stream, and (III) a lower shear layer (LSL) downstream of the aft-deck plate where jet flow mixes with the freestream flow. The tri-global resolvent analysis uses the 3-D mean flow as the base state. At the resonant frequency (St=3.3), the optimal response mode shows the two-dimensional (2-D) Kelvin-Helmholtz-like roller structures in the SPSL, and at lower frequencies (St<=1) inputs result in the optimal 2-D response in the USL and LSL, indicating the dominance of shear-layer instabilities. However, the sub-optimal modes show 3-D structures in the different shear-layer regions based on input frequency. Moreover, we compare the tri- and bi-global resolvent results to reveal the modeling effect of a spanwise wavenumber on the amplification mechanisms.