Simulations of compressible swirling flows in a circular pipe

The dynamics of inviscid, compressible and axisymmetric swirling flow of a perfect gas in a straight finite-length circular pipe is studied by numerical simulations.  The flow solver is based on integration in time of the flow parameters using an explicit, first-order accurate finite-difference scheme with a second-order accurate difference formulation in the axial and radial directions. Perturbed flow evolution at various levels of the incoming flow swirl ratio and at various subsonic flow Mach numbers is described, including decaying dynamics of perturbations when the swirl ratio is below the critical level and evolution to vortex breakdown states when the swirl ratio is below the critical level. Computed results are compared with the theoretical predictions from the studies of Rusak, Choi & Lee (2007) and Rusak, Choi, Bourguard & Wang (2015).