Cavitation tunnel

A cavitation tunnel is a closed-circuit water tunnel that recirculates flow past a model propeller or foil while the absolute pressure in the test section is lowered to reproduce full-scale cavitation numbers. Matching sigma = (p_0 - p_v) / (0.5 rho n^2 D^2) at model scale is the controlling similarity law, so the tunnel runs partly evacuated to drop p_0 and a deaerator strips dissolved gas that would otherwise trigger spurious nuclei. Stroboscopic and high-speed imaging record sheet, tip-vortex, and cloud cavitation patterns and hull pressure pulses. Large facilities add a wake screen or a dummy hull upstream to set the correct non-uniform inflow, since cavitation extent depends on the wake peak the blade meets at top dead center.