Flow behaviors and throttle effects of high-pressure air flow through orifices

In this study, the flow behaviors and throttle effects of high-pressure air flow through orifices were experimentally investigated in a pipe system and numerically simulated using Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) k-omega turbulence model. Three orifice configurations with porosities (orifice hole area to pipe area ratio) of beta = 28.4%, 7.1%, and 1.8% were comparatively evaluated under four different inflow pressures, i.e., p(in)= 1, 2, 3, and 4 bar. The numerical results agreed well with the corresponding experimental measurements. A primary recirculation with a smaller secondary recirculation region was formed immediately behind the trailing face. In the presence of supersonic flow, the streamwise velocity exhibited periodic oscillations, increasing at the expansion wave and decreasing at the shock wave region. The throttle effects were highly sensitive to the orifice porosities and the inflow conditions. In the beta = 28.4% configuration, shock waves and expansion waves were evident under different inflow pressures and alternately dominated the downstream flow, leading to periodic streamwise temperature variations, with the minimum temperature reaching -160 degrees C at p(in)= 4 bar. For the orifice with beta = 7.1%, the expansion and shock waves appeared at p(in)>= 2 bar, and continuously expanded with intensified flow fluctuations at p(in)= 3 and 4 bar, with the minimum temperature reaching -120 degrees C. For the orifice with beta = 1.8%, the impact of shock waves on the temperature field was barely observable under p(in)= 1 and 2 bar due to the small porosity. When p(in)>= 3 bar, similar temperature patterns with larger-porosity orifices were observed downstream of the orifice trailing face but were smaller in size.