  Compressible vortex rings, usually formed at the open end of a shock tube,
often show interesting phenomena during their formation, evolution, and
propagation depending on the shock Mach number (Ms) and exit flow conditions.
The Mach number of the translating compressible vortex rings (Mv) investigated
so far in the literature is subsonic as, the shock tube pressure ratio (PR)
considered is relatively low. In this numerical study we focus on low to high
vortex ring Mach numbers (0.31 < Mv < 1.08) cases with a particular focus on
very high Mv cases that are not been reported in experiments as, it is
difficult to obtain in laboratory. Using hydrogen as a driver section gas
inside the shock tube, a supersonic compressible vortex ring (Mv > 1) is
obtained for first time. It is established that the SST k-{\omega} based DES
turbulent model replicates the experimental observation better than the
previously published results at different stages of development of the vortex
ring. DES, which is an inbuilt hybrid of LES and RANS approaches is evoked that
can automatically switch to the sub-grid scale (SGS) model in the LES regions
(i.e. with different scale vortical structures) and to a RANS model in the rest
of the region (i.e. where the grid spacing is greater than the turbulent length
scale). The DES model can predict characteristics of the shear layer vortices
as well as counter-rotating vortex rings (CRVRs) as reported in the
experimental measurements. Formation of multiple triple points and the
corresponding slip-stream shear layers and thus multiple CRVRs behind the
primary vortex ring at different radial locations, in addition to the usual
CRVRs, appears to be a unique characteristic for high Mach number vortex rings.
For high PR, H2, case during formation stage, a vortex layer of reverse
circulation (that of primary vortex ring) is formed (contd...)
