Experimental study of the incidence effect on rotating turbine blades

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Incidence is an important design parameter in the design of turbine blades, and many experiments have been conducted to ascertain an optimum incidence. However, most experiments were conducted in linear or annual cascade rows. From those experiments, one can recognize an optimum incidence that can minimize pressure losses in the passage. However, the optimum incidence suggested by the experimental results in the cascade rows could be unsuitable as a design parameter in the design of rotating parts. In this study, a turbine rotor instead of the cascade rows is used to find an optimum incidence in a rotating state. An experiment is conducted in a low-pressure and cold state with a single-stage axial-type turbine. The rotational speed and turbine output power are controlled by a dynamometer. Total-to-total efficiencies are obtained at several off-design points. Mass flow rate, torque, rotational speed, pressures and temperatures are measured at inlet or exit. Five different rotor discs are used to get some variation of blade inlet angle so that the rotor operates with different incidence even though it rotates at the same speed; that is, five cases are tested and compared with the total-to-total efficiencies obtained at various incidence angles. Experimental results show that the incidence on the rotor has a great influence on the turbine efficiency, and the optimum incidence depends on the input power as well as the rotor blade profile. The range of applicable incidence becomes narrow when the turbine operates at high input power, and turbine efficiency quickly drops down as the incidence grows to negative over the range of applicable incidence.