A steady-state method for the determination of casing convective heat transfer coefficient and reference free-stream temperature in an axial flow turbine

The present study explains a steady-state method of measuring convective heat transfer coefficient on the casing of an axial flow turbine. The goal is to develop an accurate steadystate heat transfer method for the comparison of various casing surface and tip designs used for turbine performance improvements. The free-stream reference temperature, especially in the tip gap region of the casing varies monotonically from the rotor inlet to rotor exit due to work extraction in the stage. In a heat transfer problem of this nature, the definition of the free-stream temperature is not as straight forward as constant free-stream temperature type problems. The accurate determination of the convective heat transfer coefficient depends on the magnitude of the local free-stream reference temperature varying in axial direction, from the rotor inlet to exit. The current study explains a strategy for the simultaneous determination of the steady-state heat transfer coefficient and free-stream reference temperature on the smooth casing of a single stage rotating turbine facility. The heat transfer approach is also applicable to casing surfaces that have surface treatments for tip leakage control. The overall uncertainty of the method developed is between 5 % and 8 % of the convective heat transfer coefficient.