Numerical investigation of the shock formation process in underexpanded jets

Supersonic jets can be found in a wide range of aeronautical applications. The general shock structures underlying both free and impinging underexpanded jets is well understood. The present numerical investigation is an attempt to characterise the shock formation process of underexpanded impinging and free jets. To do this, a moving planar shock is passed through a pipe into the ambient air. The resulting flow field exhibits the characteristics of either a highly or moderately underexpanded jet depending on the shock propagation speed. In the present study, a planar shock travelling at Ms =1.5 and 1.8 was used to reproduce the shock diamonds and Mach disks commonly associated with moderately and highly underexpanded jets respectively. The study revealed that the the inner, outer and tail shocks are formed near the pipe wall along with the production of a large convecting vortex rotating in the counter clockwise direction.