Simulation of convective flow and thermal conditions during ultrasonic treatment of an Al-2Cu alloy

•A new approach to simulating the effect of ultrasonics on convection and thermal gradients has been developed.•The simulation shows that colder sonotrode during ultrasonic treatment creates a favourable environment for crystal nucleation on or near the radiation surface.•The convection transports all grains formed on or near the sonotrode into the bulk of the melt and creates a low temperature gradient throughout the melt which favours the formation of an equiaxed grain structure.•Convection is dampened with an increase of the solid fraction.