An experimental investigation on instability of transpiration cooling with phase change

Transpiration cooling using liquid coolant has been proven to be one of the most potential thermal protection techniques for hypersonic vehicles. However, the drastic pressure variation during phase change of liquid coolant may result in unsteady cooling effects, and this complicated problem has not been studied in detail, up to now. This paper presents the experimental investigation and theoretical analysis on the unstable performances of transpiration cooling with phase change. The experiment is carried out at four mainstream temperatures and four coolant injection ratios in the electric heating wind tunnel at University of Science and Technology of China (USTC). The results indicate that under a certain mainstream temperature and a range of coolant injection ratios, the transpiration cooling will never reach steady state, but fluctuate periodically instead. Particularly, the regular cooled wall temperature fluctuation of the entire plate surface and synchronous drastic variation of coolant chamber pressure under the complex action of capillary force and severe phase change are first captured. For the instant, under the condition of T∞ = 573 K and F = 0.28%, the entire surface temperature fluctuates regularly with a period of 197s, and a pressure peak of 23750Pa occurs in the coolant chamber. Then the essential reason of the fluctuation phenomenon in transpiration cooling is lucubrated theoretically, and the characteristics and influence factors are quantitatively analyzed.