Effect of vortex circulation on injectant from a single film-cooling hole and a row of film-cooling holes in a turbulent boundary layer, Part 2: injection beneath the vortex upwash
Ligrani, Phillip M.
Subramanian, Chelakara S.
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Results are presented which illustrated the effects of single embedded longitudinal vortices on heat transfer and injectant downstream of a row of film-cooling holes and downstream of a single hole in a turbulent boundary layer. Attention is focussed on the changes resulting as circulation magnitudes of the vortices are varied from 0.0 to 0.144 m2 /s. Mean temperature results are presented which show how injectant is distorted and redistributed by vortices, along with heat transfer measurements and mean velocity surveys. Injection hole diameter is 0.952 cm to give a ratio of vortex core diameter to hole diameter of about 1.5-1.6. The freestream velocity is maintained at 10 m/s, and the blowing ratio is approximately 0.5. Film-cooling holes are oriented 30 degrees with respect to the test surface. Stanton numbers are measured on a constant heat flux surface with a nondimensional temperature parameter of about 1.5. The situation studied is one where the middle injection hole is beneath the vortex upwash. For all results, vortex centers pass well within 2.9 vortex core diameters of the middle injection hole. To quantify the influences of the vortices on the injectant, the parameter S is introduced, defined as the ratio of vortex circulation to injection hole diameter times mean injection velocity. The perturbation to film injectant and local heat transfer is determined by the magnitude of S. When S is greater than 1.0-1.5, injectant is swept into the vortex upwash and above the vortex core by secondary flows, and Stanton number data show little evidence of injectant beneath the vortex core and downwash near the wall for x/d only up to about 17.5. For large x/d, local hot spots are present, and the vortices cause local Stanton numbers to be augmented by as much as 25 percent in the film-cooled boundary layers. When S is less than 1.0, some injectant remains near the wall beneath the vortex core and downwash where it continue to provide some thermal protection. In some cases, the protection provided by film cooling is augmented because of vortex secondary flows which cause extra injectant to accumulate near upwash regions.
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