Choice and Limits of a Fluid Model for the Numerical Study in Dynamic Fluid Structure Interaction Problems

Abstract

This paper is related to the study of a nuclear propulsion reactor prototype for the French Navy. This prototype is built on ground and is to be dimensioned toward seismic loading. The dynamic analysis takes the coupled fluid structure analysis into account. The basic fluid models used by design engineers are inviscid incompressible or compressible. The fluid can be described in a bidimensional by slice or a three-dimensional approach. A numerical study is carried out on a generic problem for the linear FSI dynamic problem. The results of this study are presented and discussed. As a conclusion, the three-dimensional inviscid incompressible fluid appears to be the best compromise between the description of physical phenomena and the cost of modeling. The geometry of the reactor is such that large displacements of the structure in the fluid can occur. Therefore, the linearity hypothesis might not be longer valid. The case of large amplitude imposed oscillating motion of a cylinder in a confined fluid is numerically studied. A CFD code is used to investigate the fluid behavior solving the NAVIER-STOKES equations. The forces induced on the cylinder by the fluid are computed and compared to the linear solution. The limit of the linear model can then be exhibited.

Fluid Forces on a Circular Cylinder Subjected to a Transient Motion at Low Amplitude: Infinite Medium and Cylindrical Confinement

“…This formulation will then be applied to the particular movement Eqn. (1). This method consists of obtaining a general formulation of forces from a solution developed for an harmonic motion.…”

“…A global R& D approach has been developed by DCN Propulsion for industrial applications. In a first step, numerical simulation techniques for the coupled fluid-structure problem were investigated [1]. A second step is now undertaken within a collaborative research program between DCN PROPULSION and LABORATOIRE DE THER-MOCINÉTIQUE DE NANTES in order to study the fluid forces acting on a moving body and to describe the physical phenomena occurring in the fluid domain.…”

Fluid Forces on a Circular Cylinder Moving Transversely in Cylindrical Confinement: Extension of the Fritz Model to Larger Amplitude Motions

“…The unit normal n which is orthogonal to T can then be evaluated thanks to Eqns. (11)(12)(13)(14)(15)(16). Its truncation at the leading, first and second orders are respectively:…”

A Review of Fluid Forces Induced by a Circular Cylinder Oscillating at Low Amplitude and High Frequency in Cylindrical Confinement

“…It consists of studying the flow induced by a circular cylinder moving in a direction normal to its axis in a fluid initially at rest. A first approach was to consider added mass effects in fully coupled fluid-structure problems [13,14]. Interest was put on harmonic oscillations in a cylindrically confined fluid.…”