Evaluation of Fluidelastic Forces in Axial Flow With Simplified Computational Fluid Dynamics

The nuclear industry is demanding low cost methods to prevent flow induced vibrations, which are a major cause of wear and damage of components such as core control bars.

An original model to compute the fluidelastic forces in axial flow is introduced in order to predict flutter. To carry on the calculation, a modal shape displacement is assumed and the Navier-Stokes equations are linearized, simplified and solved assuming the superposition of two independent velocity fields:

• $V→0(M)$ is the steady-state flow along the fixed body, computed with a turbulent k-ϵ model;

• $u→(M,t)$ is the potential flow associated with the vibration in “still” fluid.

The case of an uniform annulus is treated first, then a step variation is considered and finally the approach is extended to any parallel flow configuration. This method enables to compute the added mass, damping and stiffness coefficients and the structure in-flow eigenvectors without new algorithm.

Comparisons with the works of Païdoussis (1973), Gibert (1988), Perotin and Granger (1992) are presented here. Some rigid body laboratory tests are discussed and a satisfactory agreement between the predicted damping coefficient, the flutter occurrence and the experimental results is achieved.