Effect of Pore Blockage on Transpiration Cooling With Additive Manufacturable Perforate Holes

Transpiration Cooling is an effective cooling technology to protect hot section components such as gas turbine airfoils, rocket heads and space craft. This external cooling method has much higher efficiency than film cooling with holes when consuming the same amount of coolant, due to the uniformity of coolant distribution. However, pore blockage, which frequently occur during the operation of transpiration cooled components, prevented its application in turbine components which require long term stability. Dust deposition was one the main reasons causing blockage of pores for transpiration cooling. A lot of effort was devoted into dust deposition and erosion while optimization for the components themselves were generally difficult as the blockage caused by dusts was unpredictable for traditional sintered porous media. Additive manufacturing, with capability to precisely construct structures in small scales, is a considerable tool to enhance the controllability of porous media, and furthermore, to find a good solution to minimize the blockage disadvantage. Present study selected a cooling configurations containing perforate straight holes with an additive manufacturable diameter of 0.4 mm. Computational Fluid Dynamics (CFD) methods were utilized to model the pore blockage and its effect on heat transfer. A scripting code in addition to the ANSYS CFX solver was utilized to simulate the random blockage conditions of the holes. Two hundred numerical cases with four different blockage probabilities were calculated and statistically evaluated to quantify the disadvantage of pore blockage on the cooling effectiveness. Results obtained from the numerical analysis indicated that the overall blockage ratio was a dominating parameter for the cooling effectiveness. Upstream regions of the cooled surface were more sensitive to local blockage compared to downstream regions. Randomness of the cooling effectiveness increased with the increase of blockage probability. Present study provided a quantitative understanding of the random blockage disadvantage on the specific transpiration cooling configuration, and could benefit further optimization effort to reduce the blockage disadvantage of transpiration cooling using additive manufacturing.