Separation dynamics of a spherical particle detaching from a two-dimensional ramp in hypersonic flow

Abstract

In this work, the trajectories of spherical particles shed from the surface of a simple two-dimensional ramp in high-speed flow are examined numerically and experimentally. First, inviscid numerical simulations are performed, examining the interactions of the particle solely with the ramp-generated oblique shock, then including the effects of the ramp wall to understand the full separation behavior. It is found that three types of trajectories are possible: (i) direct entrainment of the particle inside the shock layer; (ii) initial expulsion followed by re-entry and entrainment; or (iii) surfing of the particle down the shock. At a relatively low hypersonic Mach number of 6, the first two types of trajectories are found to be predominant, but at higher Mach numbers (10 and 20), surfing becomes possible over a wider range of ramp angles and initial sphere positions. Viscous simulations examining the effect of the ramp boundary layer are also performed. It is found that the presence of the boundary layer decreases the initial repulsion from the wall, reducing the likelihood of type (ii) trajectories above but making surfing more likely at lower Mach numbers. Finally, experiments are performed with free-flying spheres in a hypersonic shock tunnel to verify that surfing trajectories can indeed be obtained at Mach 6.

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ORCID for Ralf Deiterding: orcid.org/0000-0003-4776-8183

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