DIRECT SIMULATION MONTE-CARLO MODEL OF LOW-REYNOLDS-NUMBER NOZZLE FLOWS

A numerical analysis of low Reynolds number nozzle flows is performed to investigate the loss mechanisms involved and to determine the nozzl e wall contour that minimizes these losses. The direct simulation Mont e Carlo method is used to simulate nitrogen flows through conical, tru mpet-shaped, and bell-shaped nozzles at inlet stagnation temperatures of 300 and 1000 K. The Reynolds number of the flows based on throat di ameter range from 90 to 125. The trumpet-shaped nozzle has the highest efficiency with the unheated flow. With the heated flow both the trum pet and hell-shaped nozzles have a 6.5% higher efficiency than the con ical nozzle. The conical nozzle has the highest discharge coefficient, which is unaffected by the change in stagnation temperature; however, the increase in stagnation temperature increases the heat-transfer an d viscous losses in the boundary layer. These results suggest that the trumpet-shaped wall contour performs most efficiently except near the throat region, where it incurs large viscous losses. However, the bel l-shaped nozzle may increase its overall performance with an increase in stagnation temperature.