Parametric CFD design of cold spray nozzles for metal deposition by the Method of Characteristics

The study aims to improve on the metal particle delivery of current commercial cold spray nozzles by performing a multi-objective optimization of the nozzle inner wall profile. The nozzle inner wall is varied by changing the nozzle inlet convergent angle, the throat radius of curvature, and the inflection angle. This is done using two aerospace design codes based on the Method of Characteristics (MOC). By using coupled Eulerian-Lagrangian Computational Fluid Dynamics (CFD) simulations, the performance of a current commercial cold spray nozzle is compared with that of the redesigned nozzle profiles. The design performance is then assessed by evaluating a penalty function for the different nozzle shapes. The penalty function combines some of the most desirable characteristics in cold spraying, namely: a high particle impact velocity, a uniform particle velocity distribution, and a high degree of spatial uniformity of particle distribution.

The numerical predictions show that the new nozzle shape delivers a more radially uniform deposit. A higher particle velocity is obtained at the same operating conditions/costs used by the industry standard nozzle. Flow analysis shows further performance is available by lengthening the nozzle, owing to the high Stokes number. This study shows the potential of this integrated, multi-objective, parametric design approach that can be built up in complexity to further improve the deposition performance of cold spray nozzles. It can also be used for predicting the best nozzle configuration for the application of interest, such as coating, dimensional restoration, or additive manufacturing.