Gas Turbine Flow and Heat Transfer

Vortex Model
This sketch shows a model of the secondary (vortex) flow that was determined using flow visualization techniques. Horseshoe vortices form at the elading edges of the blades. The suction side legs wrap around the suction surface, while the pressure side legs move across the passage from the neighboring blade. As they merge, the suction leg(s) move upward on the blade surface, while the pressure leg grows a fluid feeds it due to the pressure gradient in the passage. The suction leg eventually wraps around the stronger vortex (pressure leg) and a new wall vortex froms in its absense.

These vortices all play a large role in the heat transfer to the blades in these regions. The variation in the heat transfer coefficient can be quite strong depending on the direction of the local velocities in the vortices. The mass transfer method used in the measurements to follow, offers a detailed picture of these variations that would be much more difficult to measure with other techniques.