Comparison of Heat Transfer Measurement Techniques on a Transonic Turbine Blade Tip

Abstract

The present study considers spatially resolved surface heat transfer coefficients and adiabatic wall temperatures on a turbine blade tip in a linear cascade under transonic conditions. Five different measurement and processing techniques using infrared thermography are considered and compared. Three transient methods use the same experimental setup, using a heater mesh to provide a near-instantaneous step-change in mainstream temperature, employing an infrared camera to measure surface temperature. These three methods use the same data but different processing techniques to determine the heat transfer coefficients and adiabatic wall temperatures. Two of these methods use different processing techniques to reconstruct heat flux from the temperature time trace measured. A plot of the heat flux versus temperature is used to determine the heat transfer coefficients and adiabatic wall temperatures. The third uses the classical solution to the 1D nonsteady Fourier equation to determine heat transfer coefficients and adiabatic wall temperatures. The fourth method uses regression analysis to calculate detailed heat transfer coefficients for a quasi-steady-state condition using a thin-foil heater on the tip surface. Finally, the fifth method uses the infrared camera to measure the adiabatic wall temperature surface distribution of a blade tip after a quasi-steady-state condition is present. Overall, the present study shows that the infrared thermography technique with heat flux reconstruction using the impulse method is the most accurate, computationally efficient, and reliable method to obtain detailed, spatially resolved heat transfer coefficients and adiabatic wall temperatures on a transonic turbine blade tip in a linear cascade.

Aerothermal Performance of Shroudless Turbine Blade Tips with Relative Casing Movement Effects

“…Measurement uncertainties for the heat transfer taken using the Impulse method are discussed by O'Dowd et al [34]. Since the apparatus and setup are essentially identical, the quantified uncertainties are also valid in the present study.…”

“…This reconstruction is described by O'Dowd et al [34]. The linear relationship between tip heat flux and wall temperature during each blow-down run determines local heat transfer coefficients (1).…”

Ramp Heating in High-Speed Transient Thermal Measurement With Reduced Uncertainty

“…This method has been employed in a series of previous studies (Zhang et al [17,18] and O'Dowd et al [26]) and proved to be accurate, computationally efficient, and reliable. To account for the preheating before the turning on of the mesh heater, the complete surface temperature data from the start of the blowdown run were used to reconstruct the heat flux history.…”

Full-Coverage Film Cooling: Heat Transfer Coefficients and Film Effectiveness for a Sparse Hole Array at Different Blowing Ratios and Contraction Ratios

“…These data are produced using the impulse response method described by Oldfield [23]. It was later used in conjunction with infrared thermography to measure heat transfer characteristics on turbine blade tips by O'Dowd et al [24]. It was later used in conjunction with infrared thermography to measure heat transfer characteristics on turbine blade tips by O'Dowd et al [24].…”

“…According to O'Dowd et al [24], this process is more sophisticated than earlier techniques employed for heat flux reconstruction, with a filter design which is accurate to the order of 10 À12 , and reductions in processing time by a factor of 60 over finite difference approaches. The impulse method uses discrete deconvolution and known pairs of exact solution values to derive an impulse response digital filter, which is used in conjunction with a fast Fourier transform to reconstruct the heat flux from surface temperature variations.…”