DSMC Simulation of Axial and Radial Spreading of the Feed Gas in a High Speed Rotating Cylinder.

The main focus of this work is to characterize the axial and radial spreading of the feed gas introduced into the high speed rotating cylinder at different axial and radial locations for wall pressure in the range 20 to 100 m-bar using two dimensional Direct Simulation Monte Carlo (DSMC) simulations. The feed gas is accelerated through collisions with the surrounding rotating gas molecules, and there is a slowdown of the rotating gas molecules near the feed injection point, and the slow-down (V_{θ, solid body rotation} – V_θ) decreases with the increase of axial distance away from the feed point in a very complex manner, with initial slow reduction, and then rapid decrease to zero value. An important finding is that at a given feed flow rate and feed gas temperature, the axial and radial spreading of the feed gas decreases with the increase of wall pressure, and at 100 m-bar wall pressure the axial spreading continues up to the 0.141 Z, with radial spreading up to 0.733 R_wall ((Pradhan & Kumaran, J. Fluid Mech., vol. 686, 2011, pp. 109-159); (Kumaran & Pradhan, J. Fluid Mech., vol. 753, 2014, pp. 307-359)). Here, Z is the effective counter-current length, R_wall is the radius of the cylinder, V_{θ, solid body rotation} is the angular velocity corresponding to solid body rotation, and V_θ is the actual angular velocity of the rotating gas after feed injection at a given axial and radial location. The DSMC simulation result indicates that the radial velocity is symmetric around the center-line of the feed point, and decreases along the radial and axial directions following a polynomial function. The DSMC simulation result also reveals that with the increase of axial feed location away from the top baffle, the radial profile of the axial mass flux becomes more flatten at the axial mid plane, and effects the counter-current circulation rate to a great extent.