Seminar: Fluid Mechanics

Blast wave interaction with straight and inclined elliptic inhomogeneities

Speaker: S Sembian
Organization: KTH Mechanics
Time: 2018-05-17 10:30
Place: Teknikringen 8


The unstable evolution of a long isolated elliptic inhomogeneity embedded in ambient air, aligned both normal and at an angle to the incident plane blast wave of impact Mach number 2.15 is investigated both experimentally and numerically. While two symmetric counter rotating vortices due to Richtmyer-Meshkov instability (RMI) are observed for the straight interaction, the formation of a train of vortices similar to Kelvin-Helmholtz instability (KHI), introducing asymmetry in the flow field are observed for an inclined interaction. During the early phase of interaction process in the straight case, the growth of the counter-rotating vortices and circulation are found to be linear in both space and time. Moreover, the normalized circulation is independent of the inhomogeneity density and the ellipse thickness, enabling the formulation of a unique linear fit equation. Conversely, the circulation for an inclined case follows a quadratic function, with each vortex in the train estimated to move with different velocity directly related to their size at that instant. Two factors influencing the quadratic nature are identified: the reduction in strength of the transmitted shock thereby generating vortices with reduced vorticity along with the gradual loss of vorticity of the earlier generated vortices.