Measuring Microparticle Acceleration in Low-pressure Supersonic Nozzles

AUSTIN ANDREWS, Nathan Bellefeuille, Hasan Celebi, Ioannis Pothos, Kaleb Siekmeier, Bernard Olson, Thomas Schwartzentruber, Christopher J. Hogan, University of Minnesota

     Abstract Number: 101
     Working Group: Aerosol Physics

Abstract
Understanding high-speed particle transport is essential for predicting particle-surface interactions in applications such as damage to thermal projection systems in dusty environments and material synthesis from cold spray depositions. We report velocity measurements of micrometer-sized particles (1.18–7.88 µm diameter) using laser Doppler velocimetry (LDV). The particles are accelerated to speeds approaching 0.9 km/s through a converging-diverging (CD) nozzle and impinge on a substrate placed just beneath the nozzle throat, under low-pressure (3–5 torr), supersonic conditions. We examine how gas type (nitrogen, helium, carbon dioxide, and argon) and particle composition/density (ferrous sulfate, ammonium sulfate) influence particle acceleration. To assess inertial mismatch between particles and gas, we define a dimensionless “velocity lag” parameter. This lag increases steadily with a modified Stokes number tailored for high-speed flows. Measured results are compared to 3D flow simulations and particle trajectory predictions, based on a CT scan of the nozzle and a drag model valid across broad ranges of Mach and Knudsen number. The simulations reproduce key trends in velocity lag, reinforcing the applicability of these drag laws to supersonic, particle-laden flows.