Session: 22-03 Advanced Aeroelastic Prediction and Validation

Paper Number: 127337

127337 - A Low Mach Preconditioned Harmonic Balance Solver for Cavity Flutter Computations 

Labyrinth seal flutter is a critical phenomenon in the turbomachinery industry, as it can lead to severe structural vibrations and potential component damage. Accurate prediction and mitigation of flutter are paramount to ensuring the reliability and performance of modern turbomachinery systems. This paper explores the numerical computation of a labyrinth seal flutter test case using a low-Mach preconditioned Harmonic Balance (HB) solver and investigates how this approach can improve flutter computations.

HB solvers have gained prominence in turbomachinery computations for their ability to efficiently capture unsteady flow phenomena and significantly reduce computational time when compared to time-domain analyses.  In labyrinth seals, however, the flow is often characterized by low Mach numbers, and preconditioning for these conditions has been shown to significantly improve convergence and accuracy. The goal of this paper is to demonstrate how to implement low Mach preconditioning in a HB solver in the frequency domain.

We employ iterative preconditioning to alleviate the stiffness associated with density-based solvers under low Mach conditions. Furthermore, we address inaccuracies linked to the classical Roe solver in low Mach scenarios by adapting it to the low Mach preconditioned governing equations.  Through the combined utilization of iterative preconditioning and a preconditioned Roe solver, this study aims to improve convergence rates and the overall quality of flutter predictions. To gain a deeper understanding of the impact of low-Mach preconditioning on HB solvers and its potential to enhance flutter prediction capabilities, we analyze the effect of the preconditioning parameters for the preconditioner proposed by Turkel et al., on the solution and on the convergence rate.

We demonstrate the method with an academic Labyrinth seal test case originally presented by Corral et al. While previous investigations have primarily relied on linearized frequency domain solvers and reduce-order models, in this research a preconditioned HB solver is applied to this test case.

Presenting Author: Pierre Sivel German Aerospace Center (DLR)

Presenting Author Biography: - Bachelors in mechanical engineering at RWTH Aachen University
- Masters in aerospace engineering at RWTH Aachen Universty
- Phd student at the Institute for Propulsion technology of the German Aerospace Center (departement: numerical methods) for 5 years on the topic of low Mach preconditioning for frequency domain solvers in turbomachinery applications

Authors:

Pierre Sivel German Aerospace Center (DLR)
Christian Frey German Aerospace Center (DLR)
Hans-Peter Kersken German Aerospace Center (DLR)
Edmund Kügeler German Aerospace Center (DLR)