Effects of standoff distance on the supersonic flow fields in cold gas dynamic spraying

In this study, the effects of standoff distance (SoD) on the supersonic flow fields (including gas and particle flow fields) during cold gas dynamic spraying are investigated by means of computational fluid dynamics. The variation of velocity, temperature, pressure and density with different SoD is elucidated through the analysis of the distribution properties of the flow fields. It is found that the shock waves in front of the substrate remarkably influence the gas and particle flow fields. The wave system of expansion waves and pressure waves come into being continuously. The velocity of gas reaches the supersonic speed at the position of the Mach disc, while it decreases sharply when the gas flow crosses the Mach disc. The optimal SoDs are 40 mm for 1 mu m particles and 50 mm for both 5 mu m and 22 mu m particles.