Experimental audit of the mixing-plane approach to turbomachinery analysisand a review of alternative multi-row techniques

Detailed numerical comparisons of pressure and how angle measurements made in stage three of a four-stage, large scale, low speed, axial compressor ar e presented. The measurements are in both the rotating and stationary frame and were obtained as part of a BRITE/EURAM collaborative study of cantilev ered and shrouded-stator compressor configurations. The numerical analysis is 3D, considers three blade rows simultaneously and incorporates multiple row effects by use of a conservative mixing-plane model allowing circumfere ntial variation at the mixing plane. The paper discusses the early results of a study sponsored by Alstom Gas Tu rbines to examine steady-state, multiple blade-row modelling techniques. Gr owth in the endwall flow region due to multi-row effects is revealed from b oth the numerical and experimental results. The numerical simulation is con ducted without altering blade gap spacings to assist numerical stability; t he axial gap is increasingly being seen as a critical performance parameter for multiple row analysis. The limitations inherent in an approach using m ixing-planes are presented and a review of alternative, more rigourous, tre atments of these effects is then discussed. These treatments attempt to ret ain the unsteady flow structure in a steady-state model by the derivation o f so-called deterministic stresses.