Experimental and numerical study on the transient temperature response and evolution during near-wall collapse of...

The near-wall collapse of cavitation bubbles is accompanied by high-speed micro-jets, localized high pressure, and transient thermal effects. The transient temperature evolution is difficult to measure directly because of its microsecond time scale and highly localized thermal response. Therefore, the temperature evolution and energy-transfer mechanism under near-wall conditions remain insufficiently understood. In this study, a combined experimental and numerical approach is adopted to investigate the transient temperature response during near-wall cavitation bubble collapse. A microsecond-resolved high-speed thin-film thermocouple system is developed for direct wall-temperature measurement during cavitation bubble collapse. A thermal-nucleation model based on the hybrid thermal multi-relaxation-time lattice Boltzmann method (MRT-LBM) is established to analyze and verify the corresponding thermal mechanism. The hybrid thermal MRT-LBM model is validated under free-field conditions by comparing the simulated bubble-radius evolution and temperature response with the experimental measurements. The asymmetric collapse, and wall-temperature evolution under near-wall conditions are then analyzed. The influence of the dimensionless stand-off distance γ on the thermal response is also examined. Experimental and numerical results indicate that the instantaneous temperature response during the near-wall collapse of cavitation bubbles can be generally divided into four stages: the shock wave-induced temperature rise phase, the liquid film compression-induced temperature rise phase, the cavitation cooling phase, and the post-cavitation plateau phase. We have analyzed the mechanisms underlying the temperature response in each stage, supported by experimental or numerical results. This study presents two valuable findings. For the first time, we measured temperature changes induced by a shock wave with a temperature change rate on the order of 10⁶ K/s and the cavitation cooling effect with a cooling rate on the order of 10⁵ K/s. These discoveries validate the feasibility of the direct temperature measurement experimental scheme for cavitation bubble collapse based on microsecond-level high-speed thermocouples, elucidate the thermal response mechanism of near-wall cavitation bubble collapse, and establish a theoretical and experimental foundation for studying thermal damage caused by cavitation bubble collapse.