Analysis of swirling and choking in diffuser using CFD analysis

Abstract

Effect of swirl on static pressure evolution, total pressure, velocity component recirculation zones and wall shear stress such parameters in conical diffuser flow is studied. Higher pressure recovery is attained with swirl addition at the exit of the diffuser without addition tailpipe. Generally, swirling may not prevent boundary layer separation due to an intermediary recirculation zone appears hence tailpipe is suitable to allow a large-scale mixing for enhancing pressure recovery process. The present study involves the CFD analysis to predict swirl effect in the diffuser which is use in subsonic wind tunnel. 1/8th part of diffuser uses for CFD analysis. Also, it has 50swirl angle, area ratio 2 and length 1.5 m. Reynolds Average Navierstoke’s [RANS] and Shear Stress Transport [SST] use to solve closing problem and turbulence modeling respectively. For solving these numerical simulations, CFX5 Ansys based solver use. Governing equation may solved by finite volume method using Software. Turbulence effect is taken into account employing the k-ε model with an enhanced wall treatment. Mass flow (0.3445) i.e. 25 m/s velocity take as initial boundary condition for steady, incompressible as well as density based flow. Reynolds number kept constant as 30*105. Result show that swirl velocity component develops into a Rankine-vortex type or a Forced-vortex type. Input swirl intensity provides minimum energy loss and leading pressure recovery to an optimum level. Total pressure, static pressure and Mach number verses mass flow graphic result shows swirl uniformity at exit ofdiffuser.