The effects of non-condensable gas on cavitating flow over a cylinder*

The effects of non-condensable gas (NCG) in cavitating flow over a circular cylinder are investigated using a homogeneous mixture model. We consider Reynolds number = 200 at different cavitation numbers (σ = 0.7 to σ = 1.0). The numerical method developed by Gananaskadan and Mahesh (2015) for the mixture of water and vapor is extended to include the effect of non-condensable gas. It is observed that the non-condensable gas has a stabilizing effect on the cavity being formed. The decrease in sound speed when the gas is added to the flow creates a damping effect, effectively decreasing the magnitudes of shock-waves generated during the cavity collapse. Thus, weaker pressure waves impinge on the body. In the bubbly shock regime (σ = 0.7), it is shown that the NCG substantially decreases the strength of the condensation shock. A shock speed equation is derived from the Rankine-Hugoniot jump conditions to explain the phenomenon. We show that this decrease in condensation shock speed in the presence of NCG is due to the decrease in the pressure ratio across the shock as it moves.