This paper reports on an experimental investigation of aerodynamic loss of a low-speed linear turbine cascade which is subjected to periodic wakes shed from moving bars of the wake generator. In this case, parameters related to the wake, such as wake passing frequency (wake Strouhal number) or wake turbulence characteristics, are varied to see how these wake-related parameters affect the local loss distribution or mass-averaged loss coefficient of the turbine cascade. Free-stream turbulence intensity is changed by use of a turbulence grid. In Part I of this paper a focus is placed on the measurements by use of a pneumatic five-hole yawmeter, which provides time-averaged stagnation pressure distributions downstream of the moving bars as well as of the turbine cascade. Spanwise distributions of wake-affected exit flow angle are also measured. From this study it is found that the wake passing greatly affects not only the profile loss but secondary loss of the linear cascade. Noticeable change in exit flow angle is also identified.
This paper, Part II of the study on wake-passing effect upon the aerodynamic performance of the turbine cascade, demonstrates the detailed measurements of the time-varying flow field downstream of the turbine cascade as well as of the moving bars. The experiment employs a single hot-wire probe to measure pitchwise distributions of the ensemble-averaged velocity at the blade midspan. The resultant data consequently provide clear images of the incident bar wakes that are bowed and directed to the suction side of the blade wake. A custom-made total pressure probe, instrumented with a miniature fast-response pressure transducer, are also adopted to understand time-resolved feature of the wake-affected stagnation pressure fields downstream of the cascade. Furthermore, a decay process of the bar wake through the test cascade is examined in detail, which serves for the discussion related to wake recovery and its impact on the stage loss.
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