Experiment study of shock structure in aqueous foams and the unsteady shock emergence at a foam/air boundary

Abstract

The interactions of shock waves initially in atmospheric air (Mach Numbers <2.4) with aqueous foams (5<foam density <90 kg m−3) have been investigated experimentally. In addition to the characterisation of general behaviour, two particular topics are reported.i) The evolution of waves in aqueous foam has been explored, including the appearance and development of double‐fronted compressive structures for a restricted range (incident shock Mach Number ≳1.7, from density <30 kgm−3) of initial conditions; possible mechanisms for the formation of double‐fronted waves are discussed.ii) The non‐steady wave refraction at a foam/air boundary and the formation of a weakened transmitted shock in the downstream air has been studied; the strength of the transmitted wave is found to be a function of the upstream shock strength and the foam density.