A non-axisymmetric endwall contouring technology has been developed in highly loaded axial turbomachinery. This paper describes the computational and experimental evaluation of our contouring approach applied in an air turbine nozzle. The geometrical parameters and the flow conditions are consistent with a modern high pressure gas turbine. In the design of the non-axisymmetric endwall, our original design concept is applied in order to improve the aerodynamic performance. The concept, derived from the governing equation of compressible flow, is verified in comparison with the previous researches. Effectiveness of our endwall contouring technology is shown in detail through the results of a computational study for the secondary flow in the vicinity of the endwall. The flow is seen to be significantly different from that of the annular endwall. The numerical results showed that the contoured endwall controlled both generation of a horseshoe vortex near the leading edge and the growth of secondary flow in the blade passage. The effective control of the secondary flow ensures more uniform flow in the front and rear part of the passage than that in the case of the non-contoured endwall. The effect also influences the increment of Mach number in the turbine nozzle and significantly changes the distribution of the total pressure loss coefficient in the main flow region. We confirmed 35% loss reduction using an air turbine test rig. Our study demonstrates the potential of the developed non-axisymmetric endwall contouring technology for enhancing the aerodynamic performance of turbine nozzles.

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