Effect of Gap Geometry on the Cooling Effectiveness of the Wheelspace Coolant Injection Upstream of a Row of Rotor Blades

An experimental investigation is performed with a linear cascade composed of five blades having the profile of the first stage rotor airfoil of a high-pressure gas turbine. Air injected through a slot located upstream of the cascade simulates the engine wheelspace coolant injection between the stator and the rotor. The flow enters the wind tunnel test section at a 45 degrees angle to the bottom endwall, with an effective blowing rate of unity. The surface downstream of the gap is coplanar to the upstream surface in the baseline configuration, and is shifted to form a backward and a forward facing step for two additional configurations. Naphthalene sublimation measurements conducted at a Reynolds number of 600,000 based on true chord and cascade exit velocity provide local heat/mass transfer coefficients on the endwall and blade surfaces. The local mass transfer data obtained for injected naphthalene-free and naphthalene-saturated air is reduced to derive detailed maps of cooling effectiveness on the surfaces downstream of the gap. An oil dot test shows the surface flow for three geometrical configurations. The combined analysis of the mass transfer and the flow visualization results provides an interpretation of how the secondary flow structure and the cooling effectiveness are affected in the three cases, giving indications for optimizing the design of the endwall and blade cooling systems.