Effects of stator/rotor leakage flow and axisymmetric contouring on endwall adiabatic effectiveness and aerodynamic loss

Experimental and computational results that document mixing of passage flow and leakage flow in the leading edge region of the rotor stage of a high-pressure turbine are presented. Of particular interest are the effects of endwall contour geometries on mixing of the two flows and on film cooling coverage by the leakage flow over the endwall. The setting is a linear, stationary cascade that represents many features of the actual engine, such as geometry, Reynolds number, approach flow turbulence level and scale, and leakage mass flow rates. Rotation, density gradient, and upstream airfoil row effects are not represented. Two endwall geometries that give quite different acceleration profiles in the airfoil row entry plane region are examined. The flowfield in the leakage flow delivery plenum, important to the mixing process, is characterized by measurements and computation. The effects of leakage flow injection on the aerodynamic losses in the passage are also measured and computed. The loss pattern at the passage exit shows the effects of boundary layers on the pressure surface, the suction surface, and the two endwalls. Passage secondary flow features, such as remnants of the passage, horseshoe, and corner vortices are visible in the exit passage loss data. The measured and computed fields are similar, though the computed fields seem to display a larger-than-real decay of turbulent transport. The effects of changes in leakage flow injection rate on the losses are minimal for the cases studied. One of the endwall geometries has been experimentally investigated, though both endwall geometries have been computationally documented. Measurements of adiabatic effectiveness on the contoured endwall show coverage only over the upstream portion of the passage, with concentration on the suction side. The effects of the horseshoe and corner vortices on mixing of the leakage and passage flows are evident in the effectiveness pattern. Computed effectiveness distributions show similar trends to those seen in the measurements; however, measured effectiveness values are generally lower than computed values, indicating the more rapid dissipation of turbulent transport in the computations than in reality. A comparison of computed effectiveness distributions shows that the dolphin nose geometry leads to better overall film cooling coverage on the endwall.