Stability and sensitivity analysis of jets in crossflow

Global linear stability and adjoint sensitivity are used to analyze the low speed jet in crossflow (JICF). The simulations and analyses are both performed on unstructured grids at a jet Reynolds number of $2000$, based on the jet exit diameter and the average velocity at the jet exit. Two jet-to-crossflow velocity ratios ($R= v_{jet }/u_\infty$), $R=2$ and $R=4$, based on the maximum jet exit velocity, are chosen to study the transition of the upstream shear-layer from absolutely to convectively unstable. The most unstable frequencies from the stability analysis correspond to shear-layer modes, and agree qualitatively and quantitatively with experiment, DNS and DMD, over both regimes. High frequency downstream shear-layer modes become prominent at the higher velocity ratio. The adjoint and wavemaker modes reveal the importance of the nozzle and the jet near-field. Low frequency wake modes and their asymmetries will also discussed.