Simulations of planar flapping jets in confined channels

Computational analyses are used to provide a more complete understanding of the mechanisms that contribute to the development of oscillating planar jets. The geometry considered is a two-dimensional jet exhausting into a blind channel, whose open end is opposite to the initial direction such that the jet must turn through 180 deg to exit. The resulting flowfields exhibit three distinct characters that depend on the channel expansion ratio and the Reynolds number. At low Reynolds numbers the flow is steady and symmetric. A symmetry-breaking bifurcation at intermediate Reynolds numbers produces steady asymmetric flows. A Hopf bifurcation at higher Reynolds numbers yields unsteady flows. Predicted critical Reynolds numbers and oscillation frequencies are presented for different expansion ratios. Solutions are obtained from the time-dependent Navier-Stokes equations by means of an incompressible formulation based on dual-time stepping via artificial compressibility.