Entrainment of fine particles from surfaces by impinging shock waves

Abstract

When a shock wave impinges on a surface, it reflects and propagates across the surface at supersonic velocity. The gas is impulsively accelerated by the passing shock wave. The resulting high-speed flow imparts sufficiently strong forces to particles on the surface to overcome strong adhesive forces and entrain the surface-bound particles into the gas. This paper describes an experimental study of the removal of fine particles from a surface by impinging shock waves. The surfaces examined in this study were glass slides on which uniformly sized (8.3 μm diameter), spherical polystyrene particles had been deposited. Shock waves were generated in a small, open-ended shock tube at various heights above and impingement angles to the surface. Particle detachment from the carefully prepared substrates was determined from images of the surfaces recorded before and after shock impingement. A single shock wave effectively cleaned a large surface area. The centerline length of the cleared region was used to characterize the efficacy of shock cleaning. A model based upon the far field solution for a point source surface shock provides a good fit to the clearance length data and yields an estimate to the threshold shock strength for particle removal.

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