Acoustic streaming and its attendant effects in the sump of a direct-chill (DC) casting process have been successfully predicted under ultrasonic treatment using the finite volume method. This numerical model couples acoustic cavitation, fluid flow, heat and species transfer, and solidification to predict the flow pattern, acoustic pressure, and temperature fields in the sump. The model is numerically stable with time steps of the order of 0.01 s and is computationally attractive for optimization studies of DC casting. The model successfully predicted the growth orientation of dendritic grains in the billet off-centre position.