Local stability of single phase jet in crossflow – an impulse response analysis

Jet in cross flow involves a jet exiting from an orifice and exchanging momentum with a cross flow. Transverse jets are used in devices such as in lean burn gas turbine combustors where fuel jets mix with an air cross flow ahead of the flame. It is therefore desirable to understand what conditions promote self-excited instabilities in these jets to improve the homogeneity of fuel air mixing.

We will present results from a 2D local stability analysis, carried out in a plane normal to the jet exit. We use an analytical baseflow model derived by Kelly and Alves (2008). We explore a parameter space spanned by the ratio of crossflow velocity to the jet velocity and the exit shear layer thickness of the jet. A spatio-temporal stability analysis is carried out by numerically evaluating the dispersion relation using a 2D Chebyshev collocation method. The aim is to determine qualitatively, the conditions under which local absolute instability occurs in the jet. The presence of these pockets promotes the occurrence of global instability in the flow and can be used to achieve better uniformity in mixing and hence lower levels of pollutant emissions from gas turbine systems.