Fluid–structure interaction (FSI) is the interaction of some movable or deformable structure with an internal or surrounding fluid flow. Fluid–structure interactions can be stable or oscillatory. In oscillatory interactions, the strain induced in the solid structure causes it to move such that the source of strain is reduced, and the structure returns to its former state only for the process to repeat.

Fluid–structure interactions are a crucial consideration in the design of many engineering systems, e.g. aircraft and bridges. Failing to consider the effects of oscillatory interactions can be catastrophic, especially in structures comprising materials susceptible to fatigue. Tacoma Narrows Bridge (1940), the first Tacoma Narrows Bridge, is probably one of the most infamous examples of large-scale failure.

Video 1: Failure of the Tacoma Narrows Bridge (November 7, 1940)

Today, replaying the failure of the Tacoma Narrows Bridge can be achieved on a student’s laptop, at least in principle.

Video 2: 2D-Simulation of the Failure of the Tacoma Narrows Bridge (Courtesy IBS Stuttgart)

Aircraft wings and turbine blades can break due to FSI oscillations. Fluid–structure interaction has to be taken into account for the analysis of aneurysms in large arteries and artificial heart valves. A reed actually produces sound because the system of equations governing its dynamics has oscillatory solutions. The dynamic of reed valves used in two strokes engines and compressors is governed by FSI.

ANSYS CFX has been famous for its CFX Tutorials, a very sophisticated collection of 35 examples covering quite many aspects of computational fluid dynamics including FSI.

You will find four of the most enlightening FSI tutorial cases right here:

- Chapter 11: Flow Through a Butterfly Valve
- Chapter 22: Ball Check Valve using Mesh Deformation and the CFX Rigid Solver
- Chapter 23: Oscillating Plate with two-way Fluid-Structure Interaction
- Chapter 27: Modeling a Gear Pump using an Immersed Solid

CFX Tutorial images and video animations are provided as is (Courtesy ANSYS).