Assessment of single passage simulations for the aeroelastic stability of a multistage centrifugal compressor

Antoine Placzek

doi:10.1088/1742-6596/1909/1/012034

Abstract

In this paper, the aeroelastic flutter stability of an impeller is investigated numerically with single passage and full annulus URANS simulations carried out on one side on a single stage configuration including a strut and the impeller and on the other side on a multistage configuration in which two additional diffusers are considered downstream. The robustness of single passage simulations relying on the use of multiple frequency phase-lagged boundary conditions is put to the test especially in the case of the multistage configuration for which both blade passage and aeroelastic effects have to be taken into account. Comparisons between single passage simulations on the single and multistage configurations indicate that the impeller-diffuser interaction acts locally on the impeller fluid-structure interface and has only little effect on the generalized aerodynamic forces. Full annulus simulations have also been carried out to assess the accuracy and efficiency of single passage simulations which introduce additional hypotheses of periodicity in the flow. Full annulus simulations are competitive in terms of wall clock since the convergence to the periodic state is faster than with single passage simulations involving the Fourier approximation of the flow field.

Highlights

The numerical modelization of the aeroelastic stability of bladed rows is commonly assessed for a single isolated bladed row
The present paper focuses on the use of Multiple Frequency Phase-Lagged (MFPL) boundary conditions in the case of a 3D multistage research centrifugal compressor whose impeller is flexible
Simulations are run for only 7 revolutions of the impeller with the multistage 360° configuration but up to 15 revolutions are performed for the multistage/single passage configuration since the convergence of the Fourier coefficients for the MFPL boundary conditions is quite long

Summary

Introduction

The numerical modelization of the aeroelastic stability of bladed rows is commonly assessed for a single isolated bladed row. The generalization of these boundary conditions to multiple unsteady perturbations has been introduced by He [4] These Multiple Frequency Phase-Lagged (MFPL) boundary conditions have been considered for multistage 3D configurations to capture the blade passage effects [6, 7] and to assess the aeroelastic stability of a single stage flexible contrafan [8]. In these cases, only two unsteady sources of unsteadiness are involved in each blade row. The prescribed displacement is propagated throughout the fluid volume and the mesh is updated at each time step as a result of a mesh deformation problem that considers the fluid mesh as an artificial elastic structure [11]

Finite Elements structural dynamics model

Results and discussion

Revolutions

Conclusion