Stéphane Aubert

Fluid Structure Interaction Problems in Turbomachinery Using RBF Interpolation and Greedy Algorithm

In an effort to provide accurate simulations of fluid-structure interactions in turbomachinery, this paper describes a powerful method to deform mesh, using interpolation based on radial basis functions (RBF). It has been assessed on a 3D annular turbine, including a tip gap. The main difficulty of this method is to define number and position of control points. A greedy algorithm is proposed to address this issue and is tested on the annular turbine and a deforming panel placed in a shock tube. Finally, the method is slightly adapted to take into account periodic boundary conditions, which allow mesh morphing for a unique interblade channel by preserving constant pitch on lateral boundaries.Copyright

GMRES Acceleration of Restricted Schwarz Iterations

We present here an analysis of the Richardson iterations preconditioned by either the restricted additive or multiplicative Schwarz operators, and the associated GMRES Krylov sub-space acceleration. The framework of study is purely algebraic and general sparse unsymmetrical and indefinite matrices are considered. It appears that restricted Schwarz operators benefit from the indirect preconditioning effect of the overlap, but also from the non-overlapping property of the restricted local operator images. Regarding the Krylov acceleration, solving the interface system instead of the primary one, is advantageous regarding memory usage and floating point operation count. This represents only a slight modification of the global algorithm, but requires exact local solves. Another advantage is that the local problems can be treated as homogeneous.

2D Elementary Geometric Decomposition to Study Flutter Motion of a Space Turbine Blisk

Within the framework of aerospace turbines, an isolated integral bladed disk is examined. The blisk presents very high eigenfrequencies with complex deformations of the blades. A 3D steady RANS com ...

Numerical Simulation of the Flow Field in a High Speed Multistage Compressor: Study of the Time Discretization Sensitivity

The following numerical investigations are performed in the frame of a research project that aims at a better understanding of the flow unsteadiness that develops in a multistage high-speed axial compressor. First, the paper presents a new version of the 3.5 stages high-speed axial compressor CREATE (Compresseur de Recherche pour l’Etude des effets Aerodynamiques et TEchnologiques), which has been designed by Snecma and is based at the LMFA (Laboratory for Fluid Mechanics and Acoustics) on a 2MW test rig. This paper is based on numerical results obtained with 3D steady and unsteady RANS computations using the CREATE configuration. The unsteady RANS simulations are carried out over the whole spatial and temporal periodicity of the compressor. The main numerical setup has been fixed according to the state of the art. Second, the effect of three different time discretizations on the flow field in CREATE is discussed. The global performance of the compressor is not significantly affected. However the change in the time discretization impacts the structure of the flow at specific locations. The main focus of this study lies on the transport of flow structures and the analysis of their interactions. A double modal decomposition method, which highlights the specific contribution of the interactions on the overall flow field, is applied for the study of the highly complex and unsteady flow field. It allows identifying which interactions are more sensitive to the change in the time discretization.Copyright

A Partitioned Strong Coupling Procedure for Simulation of Shock Wave/Flexible Structure Interaction

The prediction of FSI limit cycles involving transonic separated flows requires efficient and accurate solvers coupling techniques. Explicit partitioned strong coupling is considered in time domain, where careful attention should be paid to energy conservation at the fluid-structure interface. For all the presented results, both meshes are set up such that structural skin points and fluid boundary mesh points are collocated. The presented test case involves a shock tube in which the shock wave impinges on a cross flow flexible panel, initially at rest. Compared to experimental results, the pressure peaks and fluctuations are correctly predicted but the pressure level is over predicted as well as the displacement frequency. Results analysis explains correctly the flow physic which is shown to be weakly modified by structural damping, turbulence modeling and time discretization. This discrepancy between experimental and numerical results could been explained by the structure model, in which the panel root modeling might be questionable.Copyright