Numerical Modeling of Upstream Nozzle Effect in Supersonic/Hypersonic Impactors for Nano-Particles

In this study the performance of supersonic and hypersonic impactors under various operating conditions was analyzed using a computer simulation model. The study was focused on the effect of the nozzle upstream condition on the performance of the supersonic and hypersonic impactors. In our earlier work, the computational domain covered downstream of the nozzle with a sonic boundary condition at the inlet. In the present study, the computational domain included the upstream nozzle where the flow and particles enter with at low velocities. Axisymmetric forms of the compressible Navier-Stokes and energy equations were solved and the gas flow and thermal condition in the impactor were for evaluated. A Lagrangian particle trajectory analysis procedure was used and the deposition rates of different size particles under various operating conditions were studied. For dilute particle concentrations, one-way interaction was assumed and the effect of particles on gas flow field was ignored. The importance of drag and Brownian forces on particle motions in supersonic/hypersonic impactors was analyzed. Sensitivity of the simulation results to the use of different expressions for the drag force was also examined. It was shown that when the upstream nozzle is included in the computational model, the Stokes-Cunningham drag with variable correction coefficient and a constant Cunningham correction factor based on stagnation point properties lead to the same results. Thus these drag laws are most suitable for computer simulation studies of nano-particles in supersonic/hypersonic impactors. The computer simulation results were shown to compare favorably with the experimental data.