Session: 22-05 Flutter models

Paper Number: 101958

101958 - Efficient Pressure Mapping for the Calculation of the Dynamic Force on Reduced Order Models of Bladed Disks 

The design of bladed disks involves both fluid dynamic and structural calculations through numerical methods that involve the discretization of the domains. On the fluid side, computational fluid dynamics (CFD) software adopts a finite volume or finite element discretization, while on the structural side, models are formulated by the finite element method and are reduced using different model reduction techniques.

The fluid model and the structural model are coupled as the aerodynamic pressure induces a load on the blades, while the blade deformation changes the boundary conditions for the flow field. In industrial applications, this fluid-structure interaction problem is usually implemented only partially, adopting a one-way coupling.

In forced-response calculation, the aerodynamic pressure is calculated using the geometry obtained, including the static blade deformation (mean pressure load, centrifugal force, temperature), disregarding the dynamic part of the response. The dynamic pressure field calculated in this way is then used as a dynamic load for the structural model. On the other hand, in flutter analyses, the blade motion is prescribed according to a selected mode shape, frequency and inter-blade phase angle and is used to define the boundary conditions for the CFD model. In both the described situations, it is necessary to transfer information (pressures or displacements) between the fluid model and the structural model.

This paper describes a technique to transfer the pressure field calculated by a CFD analysis to a structural Reduced-Order Model (ROM) obtained from a high-fidelity finite element model of the disk. The generalized forces acting on the ROM are obtained as a linear mapping of the pressure computed on the boundary of the CFD domain. This mapping depends only on geometry and mesh topologies, thus it can be calculated only once in a structural analysis, while for each time or frequency step, the generalized forces are obtained through a matrix multiplication. The calculation of the mapping tolerates the small mismatches of the fluid and structure boundaries that are often present due to various reasons related to the design process. The force is accurately calculated even in the presence of high-pressure gradients and high curvature of the blade surface. The proposed technique is applied to a frontal stage of an axial compressor for illustration purpose. 

Presenting Author: Luigi Carassale Università di Genova

Presenting Author Biography: Graduated in mechanical engineering at the university of Genova. Currently PhD student working on numerical structural dynamics and reduction techniques applied to bladed disks.

Authors:

Abdelhakim Bouras University of Genova
Luigi Carassale University of Genova