Numerical investigation of the flow field and cut-off characteristics of supersonic/hypersonic impactors

The flow field and particle transport in supersonic/hypersonic impactors are investigated numerically for a wide range of pressure ratios P0/Pb, nozzle to plate distances L/Dn and nozzle diameters. The results show that in the range of 0.5 < L / D n ≤ 0.3 P 0 / P b , the flow field properties at the impactor centerline depend only on L/Dn but not on the pressure ratio. On the basis of the numerical results for the flow field, new correlations are developed for the stagnation pressure at the impactor plate, for the maximum jet velocity, and for the distance between the bow shock and impaction plate which corresponds to the stopping distance in supersonic/hypersonic impactors. The nano-particle trajectory calculations show that in the range of 0.5 < L / D n ≤ 0.25 P 0 / P b the cut-off size d50 decreases with increase in L/Dn independent of pressure ratio. Approximation functions are presented for d50 and Stokes number, St, under conditions of supersonic/hypersonic flow. Also an expression is developed for the critical Stokes number, St50, as a function of the flow properties at the nozzle inlet.