We experimentally investigate the impingement of a gas jet onto a flowing liquid metal film, focusing on the resulting free-surface deformation and the subsequent evolution of surface waves. Our results show that the bulk flow significantly influences both the deformation of the free surface and the characteristics of the generated surface waves, which is different from the classical gas jet impingement on static liquid surfaces. Under steady gas jet impingement, the periodicity of free surface waves intensifies with a dominant frequency around 10 Hz at high gas Reynolds number ${\mathrm{Re}}_g$ for a stationary liquid surface. Critically, the interaction of the bulk flow with the gas flow establishes asymmetric coupling conditions, countercurrent flow upstream and cocurrent flow downstream, which cause the momentum exchange between the gas and the surface waves to exhibit opposite trends upstream and downstream as the liquid Reynolds number ${\mathrm{Re}}_l$ increases. In addition, under the impingement of a pulsating gas jet, we use the attenuation coefficient $c$ to correlate the wave amplitude with the jet momentum at different locations. We also find that the nonlinear interaction between the bulk flow and the forced wave accelerates the nonlinear evolution and energy dissipation of the wave. These findings can help engineers design liquid metal divertors to prevent excessive liquid evaporation, dry spots, and droplet splashing, which could damage the divertor substrate.

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• Instability of free-surface flows
• Waves and free surface flows