Abstract

Incident tolerant turbine design is a major challenge for any turbomachinery designer. High Pressure Turbines experience large aerodynamic losses when operating at reduced massflow and lower RPM. Turbine performance is adversely impacted at positive incidence angles due to shifting of the stagnation point towards the pressure side. This can cause a separation bubble in the aft suction side region. In marine life, a diverse range of animals have developed wavy surfaces along their fins and bodies to prevent stall or flow separation at engine-relevant Reynolds numbers, but for incompressible fluids.

This paper describes a novel parameterization strategy for optimizing wavy-shaped airfoils to offer superior performance at off-design operation, in the present case, at positive incidence. The methodology can be applied to all types of aircraft engines: one, two, or three spool engine configurations. The parameterized geometries are compatible with existing gas turbine manufacturing processes including casting and additive manufacturing [1,2]. The objective of the optimization was to discover the appropriate waveform combinations at the airfoil leading edge, trailing edge, and suction side characterized by their amplitude, phase, and frequency, such that the airfoils offer the lowest possible pressure losses at 15 degrees positive incidence. The optimization was performed on a high pressure turbine passage, optimized for best efficiency at nominal conditions, while maintaining the same exit flow angle and massflow. The Reynolds number is 850,000. Based on 286 designs produced, the results of the optimization show a clear benefit at positive incidence, at the expense of a slightly lower performance at nominal conditions. A final comparison of the optimized rotor with stage is included in the analysis.

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