Simulation of Indexing and Clocking with Harmonic Balance

Authors

Christian Frey - German Aerospace Center (DLR)
Graham Ashcroft - German Aerospace Center (DLR)
Hans-Peter Kersken - German Aerospace Center
Dirk Schonweitz - German Aerospace Center
Maximilian Mennicken - German Aerospace Center

Abstract

The aim of this paper is to demonstrate how the harmonic balance method can be used to predict the rotor-rotor and stator-stator interactions in turbomachinery. These inter-actions occur in the form of clocking and indexing. Whereas clocking refers to the depen-dency of the performance on the relative circumferential positioning of the rotors or sta-tors, the term indexing is used when different blade (or vane) counts lead to an aperiodic time-averaged flow. The approach developed here is closely related to the one presented by He, Chen, Wells, Li, and Ning, who generalised the Nonlinear Harmonic method to zero-frequency disturbances. In particular, configurations with only one passage per blade row are used for the simulations. We validate the methods by means of the simulation of a fan stage configuration with rotationally asymmetric inlet conditions. It is demonstrated that the harmonic balance solver is able to accurately predict the inhomogeneity of the time-averaged flow field in the stator row. Moreover, the results show that the approach offers a considerable gain in computational efficiency.