Fluid-structure interaction (FSI) problems arise in a wide variety of industries. Examples include flow-induced vibration of tubes in cross-flow, liquid sloshing in fuel tanks, pumps and compressors with pressure-actuated valves, and the vibration of fan blades. In this article, we describe the es-fsi tool, which allows STAR-CD users to efficiently solve FSI problems involving small linear-elastic deformations.

es-fsi is a new methodology for solving fluid-structure interaction (FSI) problems using STAR-CD. Commercial FEM software is used to generate the mass, damping and stiffness matrices required to solve the transient structural dynamics problem. These matrices are then used by es-fsi to solve for the deformations of the structure during the STAR-CD analysis. Finally, an optional post-processing step uses the FEM software to solve for the stresses within the structure.

Unlike the MpCCI approach, the es-fsi approach is limited to linear-elastic small-deformation problems. However, this constraint allows es-fsi to use a very efficient solution technique, resulting in only a small computational overhead compared with traditional (non-FSI) STAR-CD analyses.

An example of the use of es-fsi is the liquid sloshing and structural dynamics of a large fuel tank during an earthquake. STAR-CD's volume of fluid (VOF) capability was used to analyze the free-surface fluid sloshing problem. Some representative results of this analysis are shown.

Figure 1(a) shows the shape of the oil free surface in the tank at a particular point in time, while Figure 1(b) shows the maximum principal stress and deformation of the tank (scaled by 7500x).

A second example of the use of es-fsi is a fan blade vibration calculation. The geometry of the turbofan is shown in Figure 2(a). Flow around one of the blades was modeled together with the initial bending of the blade due to centrifugal and aerodynamic forces.

The graph of Figure 2(b) shows the bending of the blade tip at the leading and trailing edges as a function of time. Initially the blade overshoots its final position, then oscillates about this point. The oscillations are then damped out by the action of the fluid, and the blade ultimately reaches its steady-state position. Note that the displacement at the leading edge is larger than that of the trailing edge, resulting in 'untwisting' of the blade.

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