IMPROVEMENT OF THE TRIPLE-PLANE PRESSURE MODE MATCHING TECHNIQUE AND APPLICATION TO HARMONIC BALANCE SIMULATIONS

Abstract

The triple-plane pressure mode matching technique developed by Ovenden and Rienstra to analyse the acoustic field generated by turbomachine components is applied to Harmonic Balance calculations. Three extensions of the original method are assessed. They aim at improving the results with respect to i) the presence of swirl, ii) radial mean flow variations, and iii) the need to filter out convective pressure fluctuations. The method is applied to three generic test cases and two realistic examples: a low-speed fan stage and a high-pressure turbine exhibiting a strong swirl in the intra-stage. The extension to include radial variations of the mean flow in the calculation of the eigenmodes considerably improves the accuracy of the results, most notably for acoustic fields with a sparse modal content. At high Mach number, the accuracy of the simplistic analytical solution for a solid body swirl performs reasonably well because the large error made on each mode is statistically counterbalanced by the large number of contributing modes. The extension that includes an additional basis of convective pseudo-modes contributes to improve the results behind a cascade of blades, where wake perturbations are strong.