Role of the Magnus effect in additive manufacturing at the scale of the micron-sized powders within the supersonic gas flow of cold spraying

This paper investigates the kinematic responses of the micron sized powder particles to the supersonic gas flow of cold spray additive manufacturing. An experimental shadowgraph observation reveals a dispersion of the particles over a wide and long zone ahead the nozzle. A computational fluid dynamics analysis of the particle/gas flow allows for identifying the potential origin of such a prominent dispersion. The computational analysis attributes to the phenomenological turbulence of the gas flow, a kinematic role due to eddies that create the spinning of the powder particles which in turn generates a Magnus force capable for deviating the trajectory of the particles from the axial direction of the flow. The phenomenological computation showed a physically realistic dispersion of the particles within the gas stream if a Magnus force is added to the motion of the particles. Simulations of different powder cases using a wide range of material density from lightweight to heavy (Al, Ti, Cu, Ag, WC) show the occurrence of the dispersion due to the Magnus force that suggests a predominant role of the Magnus effect in cold spray additive manufacturing. An analytical depiction based on the equations of motion of the particles resulted in a criterion of rotational lift coefficient much smaller than the translational drag coefficient for characterizing the phenomenological transitions of the particles kinematics depending on the particle size. These transitions are a massless like behaviour to a predominant drag behaviour, and then from a drag behaviour to a predominant drag-Magnus behaviour.