The effect of asymmetry on the absolute instability of confined jets and wakes

Abstract Jets and wakes are fundamental fluid flows that arise in a wide range of environmental and aerospace applications. They are typically studied as open systems. Here we are interested in the implications of placing the jet or wake inside of another system, as well as the implications of compliant walls. In particular, the effect of asymmetry is considered on the absolute instability properties for this internal flow, when it is transversely confined by compliant walls. Two distinct cases are considered, namely the case of two compliant walls with non-identical wall parameters and the case of identical compliant walls asymmetrically located about the fluid center line. The absolute instability characteristics are identified by following special saddle points (pinch points) of the dispersion relation in the complex wavenumber plane, and the flow’s stability properties are mapped out using parameter continuation techniques. The compliant walls introduce new modes which typically dominate the stability properties of the flow, in comparison to the case of pure shear layers. In the case of symmetrically located walls with non-identical wall parameters, it was found that the absolute stability properties are dominated by the modes linked to the more flexible of the two walls. In the case of identical walls asymmetrically confining the flow, it was found that these flows exhibit smaller regions of absolute instability in parameter space, when compared to the symmetric flow configuration.