Transverse Jet Shear Layer Instabilities: Theory and Computations

Linear stability analysis and 3D transient numerical simulations of the round jet injected normally into a crossflow are performed. The intent of this investigation is to understand the significant changes in transverse jet nearfield shear layer stability characteristics observed in recent experiments(Megerian, S., et al., Bull. Amer. Phys. Soc.), Vol. 49, No. 10, 2004.. The stability analysis used here is an extension of that in a prior study(Alves, L., et al., Bull. Amer. Phys. Soc.), Vol. 48, No. 10, 2003.. The numerical simulations use a dual-time preconditioned scheme for the low Reynolds number compressible flow(Merkle, C., Von Karman Institute Lecture Series, 1999.) as an alternative approach to the LSA. Both LSA and numerical simulations provide support for the experimental observations that indicate the possibility of a transition in the nature of the jet's Kelvin-Helmholtz instability as the crossflow velocity increases. Both approaches provide the correct trends in the Strouhal number associated with this instability as the jet to crossflow velocity ratio is varied. In addition, the studies indicate that at high velocity ratios the jet is convectively unstable, whereas at low velocity ratios the jet is absolutely unstable. This understanding and prediction of the stability characteristics is of crucial importance for transverse jet control.