High frequency blade surface temperature determination using surface mounted hotfilm gauges

Abstract

This paper describes an attempt to determine total temperature fluctuations on the surfaces of the rotor of a transonic high pressure turbine stage. The gathered results were used to evaluate the error that these fluctuations cause in the constant temperature anemometer output signal of surface mounted hotfilms. As the temperature variations in turbomachines occur at frequencies in the order of the blade passing frequency (usually several kHz), it is in most cases not feasible to measure the surface temperature directly. Therefore, an indirect method was developed which determines the temperature fluctuations from the results of two different hotfilm tests. Even though the results are subject to severe errors, the method provides interesting information on the nature of the temperature fluctuations on the blade surfaces. The results show, that in the investigated case of a transonic turbine rotor, the temperature variations did not have a significant effect on the qualitative wall shear stress. However, this might be entirely different in other set-ups, particularly when measurements are performed downstream of turbomachinery rotors.