Through-Flow Models for Mass and Momentum-Averaged Variables

Abstract

The turbomachinery through-flow equations are reformulated for mass and momentum-averaged quantities. The background of this analysis is the need for an improved assessment of the accuracy of through-flow computations. Traditional through-flow analyses are based on density-weighted averaged quantities reducing to an area average in incompressible flows. On the other hand, experimental data are usually evaluated under the form of mass-averaged quantities, particularly with regard to the overall energy balance and efficiency estimations. The transition between these two sets of quantities is usually taken into account by introducing an averaged aerodynamic blockage factor in addition to the blade blockage factor resulting from the density-averaged quantities. The present analysis provides a rigorous derivation for the momentum-averaged flow quantities and shows that some strong assumptions on the nature of the nonaxisymmetric flow components are necessary in order to justify the current practice of introducing aerodynamic blockage. The recent availability of detailed flow data in single and two-stage axial compressors allows a partial validation of these assumptions, by the comparison of the various nonaxisymmetric components.