Measurements Over a Film-Cooled, Contoured Endwall With Various Coolant Injection Rates

This paper presents the results of a study of film coverage for coolant injection through an axisymmetric, contoured endwall of a high-pressure turbine first stage vane row. Tests are done on a low speed, linear cascade. The injection is either through a single slot upstream of the leading edges of the vanes or through two slots, one upstream of the other. Because the contouring begins upstream of the leading edges, injection is in an accelerating flow region. The effects of such injection on the secondary flows within the vane cascade are inferred by means of contours of dimensionless temperature. These thermal measurements are made by slightly heating the injection stream above the main flow temperature and documenting the temperatures inside the coolant-mainstream mixing zone. The thermal results are complemented with three-component, hot-wire measurements taken near the exit plane. Performance with different injection rates is discussed. The secondary flow seems to affect the cooling flow strongly when the momentum of the injected flow is small, compared to the main flow momentum. As a result, coolant coverage is non-uniform, with most of the coolant accumulating near the suction side of the passage. As the injection momentum is increased, some pressure-side accumulation of coolant is observed. However, non-uniformity still exists, with a lesser amount of coolant in the central region and more near the suction and pressure surfaces. For the same ratio of coolant to mainstream mass flow rates, cooling through a single slot seems to give more cooling towards the pressure side than does cooling through two slots. With the same mass flow rate, the one-slot case has higher injection momentum than does the two-slot case. This indicates that momentum flux is an important parameter in establishing the distribution of the coolant within the passage.