Simulations of planar flapping jets in confined channels

Computational analyses are used to provide a more complete understanding of the mechanisms which contribute to the development of oscillating planar jets. The geometry considered is a twodimensional jet exhausting into a blind channel whose open end is opposite to the initial direction such that the jet must turn through 180° 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 symmetrybreaking 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 artificial compressibility formulation with dualtime stepping.