FLOW AND HEAT TRANSFER CHARACTERISTICS OF TWO EFFUSED COOLING MODELS: TRANSPIRATION COOLING AND FULL COVERAGE FILM COOLING

摘要

Though both discrete hole and slot film cooling has been proved to be effective cooling methods, strong demand for further improvement of turbine blade cooling exists with the increase of turbine inlet temperature of modern gas turbine. Transpiration cooling, by replacing the cooled surface with porous wall, could be a satisfied choice for next generation high temperature gas turbine for its larger and evenly distributed cooling effectiveness. Full coverage film cooling has been severing as the main external cooling method of G class gas turbine. But the implementation of transpiration cooling in gas turbine blade cooling requires elaborated research. Numerical simulation was conducted to make a comparison of cooling effectiveness between two effused cooling models: porous plate model and inclined-multi holes model with the same coolant mass flow rate. For the porous plate model, the flow resistance for porous plate was simulated with the packed bed formula, and the porosity studied was 0.33. For the inclined-multi holes model, the geometry consisted of 10 rows of cylindrical round holes in staggered arrangement, which were angled at 20 degree. The study covered 4 blowing ratio of M=0.5, 1.0, 1.5, 2.0, and the coolant-to-mainstream density ratio was equal to 2. The influence of Reynolds number within the coolant duct was considered by covering the case of Rec=3000. The 3 dimension geometric models were meshed with a structured, multi-block grid containing about 1 million elements for inclined-multi holes model and 0.3 million elements for porous plate model. The steady state Reynolds- averaged Navier-Stokes equations with turbulence closure of RNG k-ε turbulence model were solved with the aid of FLUENT.Based on the laterally averaged cooling effectiveness over the investigated plate, the two effused cooling models studied in this paper were much higher comparing with the traditional slot film cooling. Detailed flow and heat transfer characteristics of the two effused cooling models were compared.