A comparative study of cooling mechanisms in effusion and TPMS-based transpiration cooling

Additively manufactured transpiration cooling based on triply periodic minimal surface (TPMS) lattices has emerged as a promising thermal management strategy for next-generation gas turbines. However, the relative contributions of external film cooling and conjugate heat transfer (CHT), comprising internal convection and solid conduction, remain unclear. This study experimentally quantifies these contributions by independently measuring adiabatic film effectiveness (AFE) and overall film effectiveness (OFE) using pressure-sensitive paint (PSP) and temperature-sensitive paint (TSP), respectively. Three configurations were investigated: baseline effusion cooling with zero compound angle, effusion cooling with a 45° compound angle, and Koch-type TPMS-based transpiration cooling. The 45° compound-angle configuration enhanced both AFE and OFE relative to the baseline by improving lateral coolant spreading and suppressing jet lift-off, with the improvement primarily attributed to enhanced film cooling. TPMS-based transpiration cooling achieved substantially higher AFE and OFE over the investigated injection ratios through more effective coolant-film formation and enhanced internal heat transfer. CHT remained the primary contributor to the overall cooling performance of both effusion configurations, whereas film cooling became dominant for the TPMS configuration. The temperature-based comparison of AFE and OFE suggests a greater relative role of external film cooling in the investigated Koch-type TPMS configuration than in the effusion configurations under the tested conditions.