Velocity Measurements in Film Cooling Flows

Streamwise Injection:

Streamwise Injection U Profile Streamwise Injection V-W Profile

Both of these figures show typical streamwise injection film cooling flow patterns. The film cooling hole is located at z=0. In the first figure, the streamwise velocity distribution is shown. We can see that the film cooling injection flow acts as a flow blockage, producing a region of decreased velocity downstream of the hole, with a region of higher velocity around the periphery of this blockage as the remaining flow accelerates around the blockage.

The second figure shows the cross-stream velocity components. In this plot, you can see the pair of "kidney vortices" typical of a film cooling flow.

Lateral Injection:

Lateral Injection U Profile Lateral Injection V-W Profile

In these figures, we show the same plots as above, but for lateral injection (injection is in the -z direction) instead of streamwise. Comparing these to the above images, we can see that the lateral injection flow presents a larger obstacle to the approaching flow, and hence a large region of decreased velocity. Like the streamwise flow, around the periphery of the low-velocity region we can see the flow accelerating around the blockage. Also, the entire flow pattern is "skewed" in the -z direction by the momentum of the injection jet.

Looking at the cross-stream velocity components, we can see that the "kidney vortex" pattern present in the streamwise injection flow is no longer present, being replaced by a larger scale vortex moving the freestream fluid towards the blade surface, resulting in a higher heat transfer coefficient, and hence poorer cooling performance.

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