Large eddy simulation of film cooling from cylindrical holes partially blocked by CaO-MgO-Al2O3-SiO2

CaO-MgO-Al2O3-SiO2 (CMAS) melting and then sticking in the film cooling holes is one of the important factors causing the cooling performance degradation of gas turbines. Large eddy simulation was used to study the unsteady flow physics, mixing heat transfer, and film cooling performance degradation of film cooling under the synergistic effect of typical blowing ratios (0.5 < M < 1.5) and blockage levels (0 < H/D < 0.75) and a particle deposition model was developed to predict the blockage characteristics. The results show that the deposition efficiency of CMAS is negatively correlated with the blowing ratio, and the CMAS blockage level increases nonlinearly with the service time. The film cooling effectiveness degradation rate of blocked cylindrical holes can be described by effective momentum flux ratio. With the increase of blockage and blowing ratio, the optimal effective momentum flux ratio increases from 0.14 to about 0.2, and the maximum cooling performance degradation rate reaches 95%. The blockage makes the coherent structures of film cooling more complex and disordered. The evolution of hairpin vortices and counter-rotating vortex pairs in spatial affects vertical mixing and lateral dispersion. The aggravation of hot-gas entrainment, coolant mixing, and flow separation are the root causes of the deterioration of cooling performance.

Automated summary

The deposition efficiency of CMAS is negatively correlated with the blowing ratio, and the CMAS blockage level increases nonlinearly with the service time. With the increase of blockage and blowing ratio, the film cooling effectiveness degradation rate also increases.