Turbine blade entropy generation rate part II: The measured loss

Using detailed boundary layer velocity measurements the profile loss, expressed in terms of local entropy generation rate, is evaluated at discrete locations along the suction surface of a turbine blade in a subsonic linear cascade at a chord Reynolds number of 1.8 × 10³ under adiabatic test conditions. The distribution of loss through the entire boundary layer is thus established with particular attention given to the comparison of the relative contributions from the laminar, transitional and turbulent regions. It is found that 75% of the entropy generation occurs in the laminar region of the blade, with transition being one of the key features of the overall loss distribution. Traditional correlation methods are considered and shown to give accurate results when compared to the experimental measurements within both the laminar and turbulent regions, the application of such correlations is however dependant upon knowledge of the onset and extent of transition. Finally it is demonstrated that an existing method for the evaluation of local entropy generation rate from measurements of wall shear stress in laminar flow, may be adapted for use in turbulent flow and hence the possibility is presented for the measurement of loss from surface mounted sensors.