Turbine Airfoil External Heat Transfer Measurement in a Hot-Cascade Free

Detailed knowledge of local external heat transfer around a turbine airfoil is critical for an accurate prediction of metal temperature and component life. This paper discusses the results of measurements of the local gas side heat transfer coefficient distribution which were performed in an annular gas turbine vane hot-cascade test facility and provides comparisons with analytical predictions. The steady state tests were performed at simulated engine operating conditions. The tests were conducted on an internally cooled airfoil with the intent to provide close to uniform coolant temperature at the mid-span of the airfoil and also to obtain a high heat flux through the wall, minimizing uncertainty. Internal coolant side heal transfer coefficients were measured through calibration tests outside the cascade by a wire heater. A calibrated infrared pyrometer was used to provide detailed airfoil surface local temperatures and the corresponding external heat transfer coefficients. The airfoil was instrumented with a number of thermocouples for both calibration and temperature measurement. A 12% freestream turbulence was generated by a turbulence grid upstream of the test cascade. The static pressure measured over the test vane agreed well with invicid predictions. Heat transfer coefficients were measured and compared to a TEXSTAN boundary layer code prediction. The influence of Reynolds number and Mach number on the airfoil external heat transfer coefficient were also studied and is presented in the paper.