Influence of machined surface roughness on thrust performance of micro-nozzle manufactured by micro-milling

This paper describes an investigation of the effects of machined surface roughness on micro-nozzle performance through computational fluid dynamics (CFD) simulations and experiment. Firstly, both ball end mill and taper end mill were used in the finish micro-milling processes for micro nozzles where different surface quality were obtained. A residue surface model for micro-nozzle was proposed and used in CFD simulation. The simulation results show that the increase of roughness causes that the outlet velocity decreases, total pressure drops and boundary layer thickness increases. The roughness increasing also leads to the deterioration of thrust performance of the micro nozzle. Secondly, a thrust measuring apparatus was designed and manufactured to evaluate the thrust performance of the machined micro nozzle. The thrust was measured at different inlet pressure for the machined micro-nozzles with different surface roughness. The measurement results indicate that the simulation results were consistent with the experiment. The nozzle with small roughness can achieve better thrust performance. Actual thrust fluctuation was caused by the incremental turbulent intensity with surface roughness.