Axial Flow Compressor and Turbine Loss Coefficients: A Comparison of Several Parameters

Abstract

Many loss parameters are used in the turbomachinery field for correlating the effects on losses of numerous geometric and aerodynamic variables associated with blade rows. The parameter most common to these correlations is the ratio of a loss parameter to a velocity parameter, here called the loss coefficient. Such loss coefficients of different forms used for compressors by Howell and the NACA and those used for turbines by Ainley and Soderberg, plus an additional one, are compared explicitly for possible use in both compressors and turbines. Over a range of Mach numbers, loss coefficient values are compared with loss levels fixed and for representative blading cascade test data, and pressure recoveries and stage efficiencies are compared with loss coefficient values fixed. It is shown that for a low Mach number the different parameters are equal and interchangeable; however, as the Mach number increases, differences appear and grow larger, so that a given combination of loss coefficient value and Mach number implies different entropy-rise values depending upon which parameter is being used. The criteria used here for comparing the different parameters are that one loss coefficient is better than another a– if its loss coefficient values corresponding to test data vary less over a significant range of Mach number, and b– if the stage efficiency implied by a fixed loss coefficient value varies in a more realistic way over a range of Mach number. The Soderberg parameter was found to be better for both compressors and turbines than the other loss coefficients investigated.