Mass/Heat Transfer in Rotating Dimpled Turbine-Blade Coolant Passages

Naphthalene sublimation measurements are made in a rotating dimpled square coolant flow passage with radially-outward flow. The coolant flow passage represents a typical internal cooling channel of a turbine blade. The dimples are in the form of hemispherical depressions and are arranged in staggered rows. In the present study, only the leading and trailing surfaces are dimpled. Measurements are made at a Reynolds number of 7,000 and 21,000 and for Rotation number of 0.2. The measurements indicate that dimples enhance surface mass transfer by a factor of about two compared to a smooth surface. With rotation, the trailing wall mass transfer is increased to nearly twice that of the leading wall mass transfer. Peak mass transfer occurs immediately downstream of the dimples, while the minimum mass transfer occurs in the dimple region itself. Higher mass transfer is also observed along the lateral edges of the dimple. The locations of the Sherwood number peaks suggest the existence of streamwise vortical structures generated from the leading and lateral edges of the dimples.