Stability of a jet in crossflow

TL;DR

This study investigates the stability and flow behavior of a jet in crossflow using DNS, revealing a transition from periodic vortex shedding to chaotic motion as the velocity ratio increases, and analyzing the first instability's origin.

Contribution

It provides a detailed stability analysis of a jet in crossflow, identifying the flow transition sequence and pinpointing the initial instability location using eigenmode analysis.

Findings

Flow transitions from periodic to chaotic with increasing velocity ratio R.

First instability occurs in the shear layer downstream of the jet orifice.

Flow exhibits asymmetric chaotic motion at higher R.

Abstract

We have produced a fluid dynamics video with data from Direct Numerical Simulation (DNS) of a jet in crossflow at several low values of the velocity inflow ratio R. We show that, as the velocity ratio R increases, the flow evolves from simple periodic vortex shedding (a limit cycle) to more complicated quasi-periodic behavior, before finally exhibiting asymmetric chaotic motion. We also perform a stability analysis just above the first bifurcation, where R is the bifurcation parameter. Using the overlap of the direct and the adjoint eigenmodes, we confirm that the first instability arises in the shear layer downstream of the jet orifice on the boundary of the backflow region just behind the jet.