Resonance from Contactless Ultrasound in Alloy Melts

Contactless ultrasound uses Lorentz forces from a secondary coil to induce ultrasonic vibrations in alloy melts. To achieve pressures high enough for cavitation, resonance is required. However, the prediction of the resonant modes for a melt in a crucible is complex, due to the transmission and reflection of sound within the crucible walls. Two acoustic models, one solving a simplified momentum equation in the time domain, the other solving the Helmholtz equation in the frequency domain are compared. The frequency domain model allows a fast sweep of frequencies for resonance tuning, and the transient model enables a more detailed analysis. Validation is against analytic test cases derived with boundary conditions specific for the liquid metal medium and against experimental data obtained in an aluminum melting crucible. Results confirm that sound transmission into the crucible walls has a significant effect on resonant frequencies and needs to be accounted for.