Surface pressure and heat transfer measurements in a turbine cascade with unsteady oncoming wakes

Unsteady surface pressure and heat transfer have been measured on a blade of a linear turbine cascade exposed to unsteady oncoming wakes generated by moving cylinders on a squirrel cage device. The Reynolds number and the Strouhal number corresponded to the values in a real turbomachine. The periodic components of pressure and heat transfer showed clear response to the unsteady wakes. However, the distribution along the blade surface of both pressure and heat transfer coefficient changed very little from phase to phase. The heat transfer results have shown that the boundary layer on the pressure side remained laminar for all cases, but that the boundary layers on the suction side became transitional under the wake disturbance. With increasing wake-passing frequency, the start of the transition moved forward. Increasing the wake-passing frequency resulted in a significant increase in heat transfer along the whole blade surface including the portions where the boundary layers were nominally laminar.