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March 1, 2022

What is Fluid-Structure Interaction?

Fluid-structure interaction (FSI) is the interaction of a fluid flow with a solid structure. Think of a wind gust rotating a turbine blade, a boat hull under wavy conditions, or the air rushing over the front panel of an F1 car. Anywhere a fluid and structure meet, FSI occurs.

Ansys Fluent and Ansys Mechanical can be coupled to simulate fluid-structure interaction, like this Ansys flag flying in the wind.

How can FSI Affect Product Design and Performance?

Understanding FSI is critical for the design of many products. Not accounting for the effect of a fluid on a solid or vice versa can result in overestimating or underestimating product performance. Consequently, the end product design may lead to unexpected and undesirable outcomes, ranging from bothersome noises to complete product failure.

Whether you're designing a bridge, aircraft, or gas turbine, understanding how the interaction of fluids and structures impacts your project requires a solution that accurately predicts and integrates both behaviors.

Applications of FSI

Designing aircraft: As a plane flies, airflow around the wing causes the wing to deform (which, in turn, changes the way the air flows, altering the wing even more). Solving the FSI in wing design dramatically increases the aerodynamic performance of the aircraft.

Modeling blood flow: To evaluate the effects of blocked blood vessels in aneurysms, FSI accounts for how blood pressure and flow velocity influence a vessel’s ability to stretch and change in size.

Predicting sound: When air flows pass over a car, surfaces like the hood and side mirrors can vibrate and radiate sound into the interior. By addressing these FSIs, engineers can adjust the design to reduce noise and increase passenger comfort.

The Role of Multiphysics Simulation in FSI

Before an FSI has the chance to compromise your product, you can predict and prevent it through multiphysics simulation.

For example, if you wanted to see how turbulence and pressure changes might affect the integrity of a hydropower turbine, your analysis would include data provided by both Ansys Fluent and Ansys Mechanical simulations. When used independently, these simulations tell you one story at a time. But when integrated through Ansys Workbench, you’ll see the most accurate prediction of how the two physics impact each other.

Workbench automatically exchanges data between simulation solvers, giving you one seamless workspace from which to navigate.

The advanced mesh mapping technology in Workbench ensures data is translated precisely from computational fluid dynamic (CFD) to finite element analysis (FEA) and back without the need to input data manually, write code, or exchange data files. This reduction in manual inputs significantly decreases errors because you set up the CFD and FEA simulations, drag and drop, and everything is transferred into one space.

Do you Need a One-way or Two-way FSI Simulation?

Modeling approaches can vary depending on the degree of physical coupling between the fluid and solid and the level of fidelity needed. For applications involving rigid body motion and conjugate heat transfer, deformations can be neglected, and the problem can be efficiently solved entirely within the CFD solver.

When stresses and deformations must be accounted for, the fluid and structural simulations are coupled to transfer data between the solvers for either a one-way or two-way coupled simulation.

Related Content: The Fundamentals of FEA Meshing for Structural Analysis

How to Perform a One-way FSI Simulation

One-way simulations are easily performed in Workbench by directly linking your CFD and FEA simulations. This is done through a simple drag-and-drop task that automatically connects your simulation's geometry and solution cells.

How to Perform a Two-way FSI Simulation

Two-way simulations are executed by linking your CFD and FEA simulations with System Coupling. This video creates a one-way simulation in Fluent, then transforms into a two-way simulation with Mechanical via Workbench. The two-way data exchange made possible through Workbench creates a simultaneous and straightforward simulation.

Use FSI to Predict and Prevent

FSI simulations help engineers prevent damage that can affect performance and lead to product failure by predicting interactions between fluid flows and solid structures. To learn more about FSI simulations, visit Ansys Workbench and check out these related resources:

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