Single and Multiple Row Endwall Film Cooling of a Highly Loaded First Turbine Vane With Variation of Loading

Abstract

This paper reports endwall filmcooling investigations with single and multiple rows of fanshaped film holes using temperaturesensitive paint (TSP). The experiments are carried out in a sixbladed linear cascade based on the geometry of a highly loaded gas turbine first vane. The film effectiveness performance of the cooling rows is investigated under the influence of enhanced nearwall secondary flow. Tests are conducted at three different loading conditions changing the profile incidence. Filmcooling injection is established at elevated coolant density ratios of 1.4 using heated carbon dioxide. Due to the finite thermal conductivity of the wall material, the heat conduction effects observed in the measured temperature fields are assessed by a newly developed data analysis based on a finite element thermal analysis and tracking algorithms along CFDcomputed nearwall surface streamlines. The results showed that the coolant trajectories are visibly influenced revealing the intense interaction between the film jets and the nearwall flow field. These effects are certainly enhanced with higher incidence leading to increased streamwise coolant consumption and reduced wall coverage. At the cascade inlet, the filmcooling injection is significantly affected by the nearwall flow field showing distinct overand undercooled regions. Due to the enhanced deflection and mixing of the film jets injected from a single row, areaaveraged film effectiveness and wall coverage decreases about 9 and 11%, respectively. With adding more cooling holes to this endwall area, the influence of the enhanced secondary flow becomes more pronounced. Hence, larger reduction in film effectiveness of 23% and wall coverage with 28% is observed. For single row injection at the airfoil pressure side, the stronger secondary flow motion with intensified streamwise mixing leads to a visibly decreased endwall coverage ratio of about 38% and maximum flow path reduction of about 41%. In this case, film effectiveness is found to be reduced up to 47% due to the small amount of coolant injected through this row. This effect is significantly smaller when more cooling rows are added showing an almost constant cooling performance for all incidence cases.