Flow Visualization Study of Passive Flow Control Features on a Film- Cooled Turbine Blade Leading Edge

摘要

A flow visualization study was conducted on a model of a film-cooled turbine blade leading edge in a closed-loop water channel at ReD = 30k. The model consisted of an 8.89 cm diameter half cylinder with flat afterbody joined at the ninety-degree point. A single radial coolant hole drilled 21.5. from the stagnation line, angled 20. to the surface generated a coolant jet transverse to the free stream. Water channel testing assessed the hydrodynamic effects of 16 surface modifications, to include a variety of dimples adjacent to the coolant hole and transverse trenches milled over the coolant hole. Compared to an unmodified coolant hole, a single row of small cylindrical or spherical dimples upstream of the coolant hole steadies the coolant at low blowing ratios. Medium and large spherical dimples downstream of the coolant hole have a similar effect. None of the dimple geometries studied affect the coolant jet at M > 0.75. A single-depth, square-edged transverse trench spreads the coolant, increasing spanwise coverage of a single coolant hole more than two times. This trench suffers from coolant blow-out above M = 0.50, but a deeper, tapereddepth trench provides very effective film cooling at blowing ratios above M = 0.50. It spreads the coolant in the spanwise direction, prevents coolant jet liftoff, and was the only geometry studied that holds the coolant tighter to the surface than an unmodified coolant hole.