Analytical and experimental assessment of two methods of determining turbine efficiency

The efficiency of a turbine may be calculated from measured test variables by several different methods. However, the literature does not contain docu mentation to aid one in determining the preferred efficiency method for par ticular test situations. Two methods commonly used for cold airflow testing of turbines, the thermodynamic and the mechanical methods, were evaluated both experimentally and using uncertainty analysis techniques. The experime ntal work involved performance testing of a next-generation, compact, high- turning-angle turbine design in which the flow contained significant high-g radient regions. The turbine efficiency was calculated from the measured te st data using both efficiency methods, and enhanced uncertainty analysis to ols were developed to evaluate the efficiency uncertainty for each method. The efficiency uncertainty equations were written in a new form to account properly for conceptual bias and correlated bias terms, The results showed that using the form of the equations developed was essential to obtaining t he correct efficiency uncertainty estimates. The efficiency uncertainty est imates obtained from the analysis then allowed a comparison of the two meth ods from which conclusions were drawn to guide in determining the preferred efficiency method for individual applications.