Profile Loss Coefficient Definitions Revisited

Abstract

A critical and integrated view on the profile loss coefficient definitions commonly used in turbomachinery is offered. By solving the compressible flow equations in boundary layers (characterized by their integral parameters) mixing at constant area the dependence of different loss coefficients (total pressure loss and kinetic energy loss coefficient, KSI) on the Mach number and boundary layer characteristics is investigated. KSI appears as the best parameter to measure the merit of the process since it is fundamentally independent of Mach number and only dependent on the boundary layer parameters. Results from expressions obtained by different formulations and levels of approximations are compared with the solution of the full set of compressible equations. KSI estimated by the expression 2θ/(t – δ*) + (δ*/t)2 is identified as the best parameter of merit to be used as profile loss coefficient. Additionally a comparison between losses from boundary layers discharging into constant area and discharging into constant pressure is given and the relevance played by the shape parameter, H, in the latter case is remarked.