### Simulations of Planar Flapping Jets in Confined Channels

- Dr. Francine Battaglia
- Fire Safety Engineering Div. (864)

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 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 degrees 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
artificial compressibility formulation with dual-time stepping.