Abstract-
In the present study, the interaction of a shock wave with an interface between
two gases which results in Richtmyer-Meshkov (RM) instability is studied
experimentally. The basic mechanism for the initial growth of perturbations on
the interface is the baroclinic generation of vorticity which results from the
misalignment of the pressure gradient in the shock and the density gradient
at theinterface. The growth of perturbations soon enters into a non-linear
regime with the appearance of bubbles of light fluid rising into heavy fluid and
spikes of heavy uid falling into light fluid. In the non-linear regime
interaction between various scales and appearance of other instabilities like
Kelvin-Helmholtz instability along the boundaries of the spikes occur which
results in the breakup of the interface. These processes lead to a turbulent
mixing zone (TMZ) which grows with time. The present set of experiments are done
in GALCIT 17-inch shock tube with Air and SF6 as light and heavy gases. The
growth of the TMZ is studied in a straight test section for single mode initial
perturbation consisting of two different wavelength and amplitude combinations
at incident shock Mach number of Ms = 1.55. The multimode initial
perturbation growth at late times is studied in a conical geometry to study the
effect of area convergence at incident Mach numbers of Ms = 1.55 and
1.39. The results are compared with experiments of Vetter which were done in the
same shock tube with a straight test section with no area convergence and at the
same Mach number.
The study of RM instability of single scale perturbations on Air/SF6 interface in a straight test section shows that the growth rate decreases rapidly with time with a small dependence on the initial wavelength persisting till late times. In the case of RM instability growth of multimode initial perturbations in a conical geometry, it is found that the interface thickness grows about 40 to 50% more rapidly than in Vetter's experiments. Laser induced scattering experimental results at late times are presented for Air/Helium gas combinations at the interface. In situations when the back of the interface is not clearly demarcated, the thickness is determined by an image processing technique. This is also used to determine the possible dominant eddy/blob size in the TMZ from the schlieren pictures. Some computational studies of spherical/planar shock interaction with spherical/planar interface will also be presented.
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