Measurement of Microparticle Acceleration in Low-Pressure Supersonic Nozzles

Understanding particle acceleration in supersonic jet flows is critical in applications including propulsion systems, particle impact modeling, and gas dynamic cold spray deposition. We present velocity measurements of micrometer-sized particles in the [Formula: see text] diameter range accelerated through a converging/diverging (CD) nozzle and impinging onto a substrate at speeds approaching [Formula: see text] with downstream (preshock) pressures in the [Formula: see text] range. Using laser Doppler velocimetry (LDV), we characterize particle velocity distributions across multiple gas compositions (nitrogen, helium, carbon dioxide, and argon) and particle chemistries (ferrous sulfate and ammonium sulfate). We introduce a dimensionless velocity lag to parameterize inertial effects and find that the degree of velocity lag increases monotonically with a modified definition of the particle Stokes number, which accounts for high-speed conditions. Measurement results are compared to particle velocity predictions based upon a three-dimensional simulation of the nozzle flow, with particle trajectories modeled using a recently developed drag model applicable to particles at variable Mach number and Knudsen number. Simulations largely capture the experimentally observed manner in which velocity lag varies with Stokes number.