Comparison of Visualized Turbine Endwall Secondary Flows and Measured Heat Transfer Patterns

Various flow visualization techniques were used to define the secondary flows near the endwall in a large scale turbine vane cascade. The cascade was scaled up from one used to generate endwall heat transfer data under a joint NASA-USAF contract. A comparison of the visualized flow patterns and the measured Stanton number distributions was made for cases where the inlet Reynolds number and exit Mach number were matched. Flows were visualized by using neutrally buoyant helium-filled soap bubbles, by using smoke from oil soaked cigars, and by a new technique using permanent marker pen ink dots and synthetic wintergreen oil. For the first time, details of the horseshoe vortex and secondary flows can be directly compared with heat transfer distributions. Near the cascade entrance, there is an obvious correlation between the two sets of data, but well into the passage the effect of secondary flow is not as obvious.