Effects of temperature on the coupled flow field of underwater jet and ventilated cavitation

To investigate temperature effects on the coupled flow field of underwater jet and ventilated cavity, systematic experiments were conducted in the HT01 closed cavitation water tunnel. Using proper orthogonal decomposition entropy analysis and 1/3-octave band noise spectrum analysis, we explored single-factor effects of temperature, inflow velocity (Froude number Fr), and ventilation rate (Cq) under gas-only jet conditions, as well as temperature impacts on coupled flow field states. Experimental parameters are as follows: jet temperature 20–700°C, Fr = 14.29–42.86, and Cq = 34.72–416.69. For gas-only jets, increasing temperature reduces gas–liquid interfacial tension, intensifies Kelvin–Helmholtz (K–H) instability, and promotes bubble breakup. At high Fr, global spatial entropy increases with temperature. Increasing Fr doubles jet penetration depth and reduces total sound pressure level by 5 dB and global entropy by 56.12%, converting large-scale low-frequency flow pulsations to small-scale high-frequency oscillations. Higher Cq expands jet influence; above Cq208.34, gas retention saturates, entropy growth slows sharply, and noise stabilizes. In the coupled flow field, cavitation morphology evolves with Cq as “Integrated Cavity (IC) → Partially Broken Cavity (PBC) → Pulsating Foam Cavity (PFC),” with distinct temperature responses: IC suppresses global disturbances to enhance flow stability; PBC enhances local disturbances, with spatial entropy increasing significantly only in the far-nozzle region via turbulent superposition; for PFC, higher temperature strengthens overall flow turbulence, expanding high-entropy region coverage and widening the entropy peak-low value gap.