| The unstable, self-excited or forced vibrations of rotor blades must be avoided in designing high performance turbomachinery components because they may induce structural failures. In evaluating the stability of such vibrations, computational approaches have been bearing an increasing role due to the surprising progress of computer technologies and advanced algorithms. They are now at a stage where fluid/structure coupled simulations of aeroelastic phenomena in turbomachinery for real geometries are in contest for practical use. The present study demonstrates the capabilities of a fluid/structure coupled computational approach which consists of an unsteady three-dimensional Navier-Stokes flow solver, TFLO, a finite element structural analysis package, MSC/NASTRAN, and the coupling interface between the two disciplines. The flow solver relies on a multi block cell-centered finite volume discretization and the dual time stepping time integration scheme with multigrid for convergence acceleration. Parallelization with multiple processors is also performed to achieve faster computations making use of the Message Passing Interface. As far as the interface is concerned, high accuracy is pursued with respect to load transfer, deformation tracking and synchronization. As a result, the program successfully predicts the aeroelastic responses of a high performance fan, NASA Rotor 67, over a range of operational conditions. The major contribution to the aerodynamic damping for turbomachinery blade motions is observed to be the unsteady pressure generated at the location of the shock. The results show that the unsteady pressure may act to damp or excite the blade motion mainly depending on the inter-blade phase angle. It is concluded that the level of sophistication in the individually sophisticated disciplines together with an accurate coupling interface will allow for accurate prediction of flutter boundaries of turbomachinery components. |
