CO₂ transpiration cooling for infrared-stealth thermal protection: An experimental and numerical study on mid-infrared radiation of a porous plate

This study investigates the dual role of transpiration cooling in thermal protection and infrared radiation regulation for high-speed aircraft. An experimental system is established using a porous plate with CO₂ as the coolant, and a dual-optical path measurement system is developed to examine the effects of coolant momentum flux ratio on cooling efficiency and total radiation power. The mid-infrared radiation characteristics of the porous plate under CO₂ transpiration cooling are analyzed through combined experimental and numerical approaches. Experimental results demonstrate that as the momentum flux ratio increases from 6.67 × 10⁻³ to 8.95 × 10⁻³, the cooling efficiency improves from 27.0% to 41.5%. Concurrently, the total radiation power in the 4.2–4.4 μm band is reduced by 19.6% to 39.5% compared to the uncooled baseline, confirming the dual effectiveness of CO₂ transpiration cooling in achieving both thermal protection and infrared stealth. Numerical analysis reveals a critical threshold for the contribution of gas film radiation to the total radiation power, identified within the momentum flux ratio range of 8.18 × 10⁻³ to 8.76 × 10⁻³. Below this threshold, gas film radiation intensifies with increasing CO₂ concentration; above it, radiation saturates due to the dominant temperature suppression effect from near-wall cooling. Furthermore, as the momentum flux ratio increases, the peak location of gas film radiation intensity progressively shifts away from the wall, providing additional insight into the coupled control of film radiation by temperature and concentration fields.