NUMERICAL UNSTEADY AERODYNAMICS FOR TURBOMACHINERY AEROELASTICITY

Anne-Sophie Rougeault-Sens and Alain Dugeai

Structural Dynamics and Coupled Systems Department Office National d’Etudes et de Recherches Aerospatiales B. P. 72, 29 avenue de la Division Leclerc, 92322 Chatillon Cedex, France Anne-Sophie. Sens_Rougeault@onera. fr, Alain. Dugeai@onera. fr

Abstract This paper presents ONERA’s recent advances in the experimental and numeri­cal understandings about the aeroelastic stability of aeronautical turbomachiner­ies. Numerical features of a quasi-3D and a 3D Navier-Stokes unsteady aeroelas­tic solver are discussed: turbulence models, grid deformation techniques, spe­cific boundary conditions, dual time stepping. A dynamically coupled fliid – structure numerical scheme is presented. Isolated profile, rectilinear cascades computational results are compared to experimental data. Results of aeroelastic Navier-Stokes computations for 3D fans are shown.

Keywords: fbid-structure coupling, aeroelasticity, turbomachinery

1. Introduction

For several years, ONERA has been interested in aeronautical turbomachin­ery aeroelasticity studies. The goal of this research has been to improve the ex­perimental and numerical knowledge about the aeroelastic stability and forced response of aeronautical turbomachineries.

One of the main challenges in this matter concerns the prediction of the aeroelastic stability of fans, especially in the case of the transonic regime. In this case, the dynamic behavior of the boundary layer needs to be accu­rately predicted using RANS numerical modeling with transport equations tur­bulence models. Numerical simulations have to be performed in a deforming grid framework using an Arbitrary Lagrangian Eulerian formulation.

In order to perform validations of the developed numerical tools, several unsteady data bases were built first for an isolated profile, and then for a rec­tilinear cascade. Theses databases have been extensively used to conduct nu­merical unsteady Navier-Stokes aeroelastic validations.

Another point concerns computational time reduction. Unsteady aeroelastic Navier-Stokes computations are extremely time-consuming due to the small

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K. C. Hall et al. (eds.),

Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines, 423-436. © 2006 Springer. Printed in the Netherlands.

time-step needed to keep the numerical scheme stable in the small boundary – layer cells. This is the reason why the numerical technique of dual time­stepping has been implemented in the various unsteady Navier-Stokes codes used at ONERA. This technique allows one to reduce the time of aeroelastic Navier-Stokes computations in such a way that simulations that would have been unaffordable using global time stepping are now possible.

The last purpose of this paper is to show some results for direct fliid – structure coupling simulations. A coupled scheme using Newmark’s time dis­cretization has been developed and implemented in our aeroelastic Navier – Stokes codes (Girodroux et al.,2003). Coupled time domain simulations have been performed in the case of a compressor fan blade.

This paper presents some of the unsteady aerodynamic numerical develop­ments and results of the experimental campaigns. Some results of the valida­tion processes of the 2.5D and 3D aeroelastic Navier-Stokes codes will be de­tailed. An example of a dynamically coupled 3D Navier-Stokes Arid-structure computation will be given.