Numerical investigations on the effect of total pressure and nozzle divergent length on the flow character and particle impact velocity in cold spraying

This study investigates the effect of total pressure (P0) and nozzle divergent length (Ld) on the flow character and particle impact velocity in cold spraying. Computational fluid dynamic (CFD) approach is employed in the present work to achieve this objective. The simulated results indicate that P0 and Ld significantly influence the flow regime and particle acceleration. With gradually increasing P0, the nozzle exit Mach number (Me) firstly increases and then fluctuates after P0 exceeds a critical value, finally Me reaches the maximum value and maintains stable. Differing from Me, the particle impact velocity (Vp) continually goes up with P0 due to the increasing gas density which can improve the drag force, but the growth rate levels out gradually. Besides, it is also found that Me shows a downward trend with increasing Ld. However, as for Vp, there exists an optimal Ld which can guarantee the particle achieving the maximum Vp. Moreover, for nozzles with larger expansion ratio, the optimal Ld is longer. This optimal length is considered as a consequence of the competition between the particle acceleration time and drag force on the particle surface.