Modeling of jet flows for straight and angled nozzles in air-plasma powder spraying

Comparative modeling of plasma jets generated by a direct-current plasma torch using straight and angled nozzles was carried out. The geometry of the angled nozzle developed by the authors was numerically analyzed; this nozzle was created for air-plasma spraying of powder coatings onto the inner surfaces of small-sized parts. The gas dynamics of the mixing of a high-temperature plasma gas jet with flows of cold carrier and focusing gases in the nozzle was studied. The proposed aerodynamic model and calculation algorithm were validated by comparison of the coordinates of shock diamonds along the jet length in the off-design mode of plasma torch operation, which showed acceptable agreement with full-scale experiments. The effect of wall cooling on the jet enthalpy was calculated, and its significant role was demonstrated in the case of using an angled nozzle. The distances and optimal gas flow rates at which the velocity and temperature profiles along the jet cross-section acquire an axisymmetric and uniform appearance were determined.