Investigation Of Film Cooling On The Surface Of Blade In A Turbine Cascade

The purpose of this investigation is to understand the flow and heat transfer characteristics of film cooling on the blade surface in a turbine cascade by means of detailed experimental and numerical simulation methods. The influences of many factors on film cooling effectiveness were also investigated.The turbine cascade test sections and turbine blades were set up according to the geometry provided by Gas Turbine Establishment of China. Experimental measurements were carried out in a large-scale low speed wind tunnel in Northwestern Poly-technical University. Firstly, the pressure coefficients distribution on the blade surface were measured with the Reynolds number of Re∞ = 250,000 - 450,000. Then, the discharge coefficients of film holes were obtained in the condition of Re∞ =100,000-450,000, BR = 0.5 -2.5 for stator and Re∞ = 250,000- 450,000, BR = 0.5-2.5 for rotor. The influence of Reynolds numbers and blowing ratios on discharge coefficients were investigated. Lastly, the film cooling effectiveness at different locations on blade surface were detailed measured in the cases of mainstream Reynolds number changing from 250000 to 450000 and blowing ratio changing from 0.5 to 2.5. The results have shown that there are three-dimentional characteristics of pressure coefficients distribution on the suction surface near the end-wall of turbine cascade. Film hole discharge coefficients were increased obviously with blowing ratio, especially in the case of low blowing ratio. The influences of location of film cooling holes on film cooling effectiveness are described. The experimental results indicate that (1)On the suction surface, the film cooling effectiveness decreases with increasing blowing ratio and is not significantly affected by mainstream Reynolds number. (2) On the leading edge, the film cooling effectiveness at the zone immediately downstream of the cooling holes is affected by blowing ratio and mainstream Reynolds number, while the effects are not important in the downstream zone far from the cooling holes. (3) On the front half of pressure surface, the effectiveness increases with decreasing blowing ratio at the downstream near the cooling row and it is contrary at the downstream far from the cooling row. (4) On the rear pare of the pressure surface, the effectiveness decreases with increasing blowing ratio and does not vary so much downstream in the cases of higher blowing ratio.The method of prediction the discharge coefficients of film cooling holes on the turbine blade suggested by D.A.Rowbury et.al has been improved in this paper to fit the computations in the cases of low pressure ratios and the holes in leading edge region especially. The effects of external cross-flow, hole geometry and Reynolds number in the hole were taken into account. An additive loss coefficient method is subsequently appliedto the test data in order to assess the effect of the external cross-flow. To compare with great deal of experimental data, the results show the improved method could be used as a generalized design methodology of film cooling for turbine blade.Predictions of span-wise averaged effectiveness are made with a two-dimensional boundary layer code using the low Reynolds number k-ε two-equation turbulent model. A new injection model, which is incorporated in the code, to describing the discrete-hole injection process had been suggested. The developed code can be used to calculate the film cooling effectiveness on the turbine blade surface successfully.Detailed numerical simulations on the three-dimentional turbulent flow and heat transfer were carried out in the case of no injection and with surface film cooling injection. RNG k-ε turbulence model and standard wall functions were used. The results show that the basic flow and heat transfer patterns of both cases were all well simulated, but further improvement on the accuracy of numerical simulation is needed.