Shock-wave propagation and gas phase growth in droplets deviating from sphericity

In this paper we present a numerical study of supersonic wave propagation in water droplets with shapes deviating from sphericity; uniformly distributed gas nuclei are assumed to be present in the droplet volume, which are subjected to growth under the influence of the passing shockwave. A homogeneous compressible mixture model is utilised together with a finite-rate relaxation approach for the liquid-gas interfacial dynamics, and validated against experimental results. The effect of varying deformation for a range of nominal droplet diameters and for Mach numbers based on the axial velocity ranging from M = 2.4 to 4.4 is reported. The results reveal that as the examined deformed droplet shapes have a shorter length in the direction of the impacting shockwave, gas phase expansion is advanced and reaches higher volume fractions. Additionally, the effect of coherent liquid-aid interfacial structures in the form of harmonic surface disturbances attributed resembling Kelvin–Helmholtz (KH) instabilities is examined. The presence of those surface disturbances lead to multiple wave reflections and wave superpositions that give rise to further amplification of pressure and stronger gas-expansion effects.