Fluid Structure Interaction & Modeling in Valve Design

Understanding how FSI can be a vital tool in designing safer, leaner, and more reliable valves.

By Arun Kumar Krishnan, Engineer – Plug & Butterfly Valves – Flowserve; Donald Prince, Engineering Specialist – Isolation Valves – Flowserve

Industrial valves operate under challenging service conditions involving high pressure, temperature, and frequent cycling. These complex environments often lead to structural deflection, sealing distortion, and unpredictable performance behavior.

Traditional analysis methods such as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) provide useful results. However, they usually treat fluid and structural behavior separately. Fluid-Structure Interaction (FSI) modeling enables engineers to study the dynamic coupling between fluid flow and structural behavior in a more integrated and realistic manner.

This article outlines the theoretical foundations of FSI, the need for its application in valve design, and the benefits it brings to product development and optimization.

Understanding Fluid-Structure Interaction (FSI)

Fluid-Structure Interaction refers to the two-way interaction between a fluid flow and a deformable structure. When internal pressure or flow velocity interacts with flexible valve components like plugs or discs, it can cause stress redistribution, shape change, or even contact loss at the sealing interface.

The structural response then changes the fluid path, further altering forces. This feedback loop is critical in applications where precise sealing, fatigue resistance, or dynamic stability is required.

Conventional analysis might miss these effects. Fluid structure interaction allows the evaluation of design behavior holistically, predict problem areas early, and improve design decisions before reaching the physical test stage.

The FSI analysis captures this in either one-way or two-way coupling in a single simulation.

A Comparison of FSI vs. Traditional Methods:

Use of FSI in Valve Engineering

Conventional approaches often oversimplify valve behavior by applying static pressure loads or assuming rigid bodies. In critical isolation valves, these matter because:

• Deformation can lead to permanent changes in the flow path or pressure distribution.
• Improper seating can lead to leaks or wear.
• Repeated cycling may affect the longevity of trims like the plug, disc, and ball.

Fluid structure interaction helps engineers simulate real-world valve behavior early in the design phase, reducing reliance on trial-and-error testing and minimizing costly redesigns. It enables engineers to:

• Predict loss of sealing contact due to pressure-driven movement.
• Visualize sleeve or disc bulging under high pressure.
• Detect uneven load distribution across valve internals.
• Identify stress concentration zones early.
• Evaluate the effects of vent holes, ribs, and seat design.
• Thermal FEA to verify the temperature distribution impacts.

These insights support material optimization, performance enhancement, and longer valve life.

FSI Modeling and Set-Up Approach

A study followed a one-way FSI approach using CFD and structural solvers. The valve was first analyzed using CFD to compute pressure loads, which were then transferred to a structural model for stress and deformation evaluation.

Key steps in the simulation included:

1. Preparing the geometry and fluid domain.
2. Running CFD simulations to capture internal pressure profiles.
3. Mapping pressure loads onto a structural model.
4. Running FEA to observe displacement, stress, and strain responses.
5. Iterating the design based on deformation trends.

Depending on the tool, a one-way or two-way coupling method can be adopted. One-way FSI assumes fluid affects structure but not vice versa; two-way FSI fully couples both fields.

Case Study: Full Port Non-Lubricated Plug Valve

A non-lubricated plug valve (sleeved plug valve) was studied using common computer aided analysis.

Finite Element Analysis (FEA) has become very user friendly to analyze a simple system; the ability to make gross assumptions that yield highly inaccurate results is very easy to do as well.

Traditional FEA of a PTFE sleeve inside the valve would include selecting all surfaces exposed to pressure. This would include the valve body water way, the port, the inner surface of the sleeve, the vent holes through the sleeve, the back of the sleeve exposed to these vents, and the valve body bowl matching the area exposed by the vent holes.

Due to the cylindrical shape of the sleeve, the outer surface would be greater than the inner surface sleeve, and the sleeve would balloon or billow inward. This does not match empirical results.

Another computer analysis technique is computational fluid dynamics (CFD). It gained popularity since it can simulate flowing systems and generate accurate estimates of the flow coefficient Cv.

Using CFD on a partially open valve, with a vent hole in the plug, it nearly aligned with a vent hole in the sleeve and indicated turbulence inside the valve, as well as flow through that plug vent, sleeve vent, and even behind the sleeve.

Just like FEA, CFD is a highly powerful tool but requires careful use and all assumption needs to be fully documented and vetted to ensure it matches reality. Empirical results show that the sleeve does not stay against the plug, the fluid does not flow through the vent, nor does it flow through the sleeve vent hole to reach the back side of the sleeve.

A highly experienced user can override these issues and add more assumptions to achieve reliable results. However, there is another option as described, FSI.

The fluid, even if already in the system, gains pressure. Many texts will say pressure is instantaneous, especially in hydraulic systems. The definition of instantaneous is misleading. The pressure rises and cascades into the system and the pressure meets with resistance when it hits the PTFE sleeve, but there are vent holes.

As the pressure is moving through those holes in much smaller compression waves, it is also forming the sleeve against the body. The chamber behind the sleeve collapses and the sleeve is formed into its intended use position. Using the CFD from the initial model and adding it as an applied incremental force into the valve, FSI can simulate this and match empirical results.

Valves can be designed to control the impact of the flow and how the resulting forces affect component integrity. Gone are the days of “bigger is better” and “just add ribs”. This type of analysis is not yet easy or user-friendly. It takes patience, time, and computational power.

As a result, valves can be streamlined for stress distribution, verified in virtual simulations, and can even be placed into more complex systems that account for media such as slurries with their erosion and cavitation issues.

We live in a great age, but FSI isn’t new. It is already being used for contact analysis between plug and sleeves disc deflection in butterfly valves under unsteady flow, seating integrity under differential pressure, as well as effectiveness for purge port locations and sizes. Each case benefits from understanding how fluid motion drives structural effects, which is Fluid Structure Interaction.

Future Opportunities and Benefits

With continued advances in simulation tools and computing power, FSI is set to become a mainstream part of digital valve design. Soon, we’ll be able to simulate hundreds of ideas virtually—and only physically test for validation, saving time, material, and cost.

Conclusion

Fluid structure interaction modeling offers a powerful way to bridge the gap between fluid flow and structural mechanics in valve design. It brings engineers closer to real-world conditions and allows smarter, faster decisions during development. As we embrace more digital workflows, FSI will be a vital tool in designing safer, leaner, and more reliable valves.

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