Contoured Holes for Film Cooling: the Effect of Kidney-Shaped Vorticles.
Final technical rept. 1 Apr 95-31 Oct 96,
WASHINGTON UNIV SEATTLE DEPT OF AERONAUTICS AND ASTRONAUTICS
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Flow visualization studies were carried out in water to ferret out the fluid dynamical mechanisms underlying the shaped holes used in film cooling. Both laser induced fluorescence and particle image velocimetry were used. The results uncovered two fundamental reasons why shaped holes work. First, by proper shaping of holes, one can increase the lateral separation of the kidney-vortices this delays the lift off of coolant jets. Second, some shaped holes are found to be conducive to what we call an anti-kidney pair, whose sense of rotation is opposite to that of the kidney pair. The anti-kidney pair, the presence and the formation mechanism of which appears to be first identified in this study, has also the undesirable effect it enters the hot crossflow into the central region of the jet and toward the surface. However, if the anti-kidney pair is properly positioned so that it can cancel the adverse effect of the kidney-pair, then the anti-kidney pair can prevent the jet lift-off. Thus the very key for the improved design of shaped holes is the manipulation of the hole geometry in such a way that the kidney and anti-kidney vortices annihilate each other.
- Fluid Mechanics