Abstract:  

This paper analysed the impact forces acting on a flat plate exposed normally to a rarefied plume issuing from a nozzle with a planner exit. The plate is assumed to be completely diffuse and the gaseous plume flow out of the exit is modelled with a Maxwellian distribution function, which was characterized with known number density, nonzero exit velocity, and temperature. The analytical collisionless flow results for drag force and shear force due to the impingement on the plate were derived. Effects of speed ratio, wall temperature, exit plume temperature, plate length and vertical distance between nozzle exit and plate center in the impact forces were studied. The results showed that the drag or shear force was directly proportional to the surface area of the flat plate. The drag and shear force increased as the speed ratio increased up to plate semi width of 0.7 m, then both forces decreased as the speed ratio increased up to the end of the plate length. The drag or shear force increased as the distance between the plate and nozzle exit decreased. In addition, the drag force increased as the plume exit temperature or plate temperature increased, while the shear force increased as the plume exit temperature increased. In considering the reflected particles from the plate or neglecting these particles; shear force was not affected, while drag force decreased when the reflected particles were neglected from the computation. Numerical simulation results obtained with the direct simulation Monte Carlo method validate the analytical collisionless flow solution for the surface pressure, shear stress distributions, and the impact forces