Numerical investigation on transpiration cooling performance with different porosities and mainstream pressure gradients

Improving transpiration cooling performance is a challenge to meet the requirements for the cooling perfor- mance and thermal stress restrict. In the current study, numerical simulations are carried out to investigate the transpiration cooling performance with different porosity configurations and mainstream pressure gradients. Eight porosity configurations, three mainstream pressure gradients, and three injection ratios are considered. Cooling effectiveness distributions and cooling effectiveness uniformities are evaluated. Velocity distributions and coolant allocations are also studied to reveal the cooling mechanism. Results show that all the transpiration cooling cases gain higher cooling effectiveness than the film cooling cases, and the maximum enhancement reaches up to 100%. However, the transpiration cooling cases have non-uniformity distributions of cooling effectiveness due to the uneven coolant allocations caused by the superposition effects. For uniform porosity configuration cases, the cooling effectiveness increases monotonically with the increasing porosity due to the enhanced external coolant coverage, whereas the uniformity of cooling effectiveness decreases due to the more uneven coolant allocation distribution along the mainstream direction, especially for the configurations with large porosity. In addition, when streamwise pressure gradients exist in the mainstream, only the TC-3 case with a small uniform porosity and the TC-8 case with a streamwise decreasing porosity perform better robustness. Among them, the TC-8 case gains obvious advantages in engineering applications due to the highest cooling effectiveness and the smallest non-uniformity, which is caused by the better coolant coverage and more uniform coolant allocation.