An Advanced Impingement/film-cooling Scheme For Gas Turbines – Numerical Study
Free (open access)
A. Immarigeon & I. Hassan
This study is a numerical investigation of a novel film-cooling scheme for high temperature gas turbine applications. The scheme combines both the advantages of traditional film cooling with those of impingement cooling. The hole that transports coolant fluid from the inside to the outside of the blade is designed in such a way that the coolant must go through a bend before exiting the blade, thus impinging on the blade material. Furthermore, flow turbulators or pin fins are located on the path of the coolant to increase the cooling performance. The flared hole exit was also designed to reduce the coolant momentum and ensure wide lateral spreading of the coolant on the downstream surface. This scheme is expected to produce the greatest coverage of the blade with the least amount of mixing, using the least possible amount of coolant. Turbulence was modeled using the standard k-ε turbulence model and two of its variants, with enhanced wall treatment. The shape of the impingement nozzle and the configuration of the pedestals inside the hole were varied in order to determine the effect of hole geometry on the adiabatic film cooling effectiveness. The blowing rates were varied between 0.44 to 1.77 based on the hole exit conditions, while the mainstream and coolant inlet temperatures were set to 1300 K and 750 K, respectively. The flow field, the temperature field, and the turbulence field were studied in great detail. The results showed that the downstream film cooling effectiveness was affected by the shape of the impingement nozzles and the pedestals configuration; recommendations were made for the best possible cooling scheme. Furthermore, the cooling jet remains attached to the surface at much higher blowing rates than for standard circular holes, indicating a superior performance for the proposed scheme. Keywords: film cooling, gas turbines, flow turbulators, CFD.
film cooling, gas turbines, flow turbulators, CFD.