Bent Pipe, Thermal FSI, ANSYS Fluent CFD Simulation

Description

In this project, we present a simulation of a Bent Pipe under Thermal FSI via ANSYS Fluent software. We have modeled a simple pipe containing two bends. The computational domain consists of a fluid zone dedicated to the water flow and a solid region as the pipe body surrounding the fluid zone.

What is FSI?

The water flows throughout the pipe with two elbows. So, the fluid flow can expose a pressure load on the inner wall of the pipe (especially in bend zones). In such a condition, analysis of Fluid-Structure Interaction (FSI) becomes important. It means that both fluid and structural calculations are available.

Why Thermal FSI?

The hot water flows throughout the bent pipe. So, it is expected that a thermal load will be imposed on the solid body. As a result, the focus is on the Thermal FSI. It means the solution data of fluid flow, structural, and thermal calculations are coupled.

1-way or 2-way?

First, the effect of the pressure and thermal loads of the flow on the inner wall of the pipe is analyzed. Next, the effect of the solid pipe structure, deformed or displaced, on the nearby flow is investigated. Hence, it is called Two-way FSI.

Methodology

For FSI simulations, we recommend two general methods: intrinsic FSI and extrinsic FSI. If the calculation of both the fluid and the structure is performed only in ANSYS Fluent, it is called Intrinsic FSI. Meanwhile, if the calculation process of the fluid and the structure is performed in different and individual solvers and then coupled with each other, it is referred to as Extrinsic FSI.

Intrinsic FSI:

In this project, we have used the intrinsic FSI method. We performed fluid and solid analyses for both the fluid and structural domains, using only the ANSYS Fluent solver. It means that no external solver is required for the interaction between the fluid and the structure.

Structure Model:

For the internal FSI, we have used the Structure model. By this option, the calculations for solids are also added to fluids.

Linear or Non-linear Elasticity?

We used the Linear Elasticity method for structural analysis. It means that the deformation or displacement of the structure is proportional to the force value exerted by the fluid.

Comparison analysis:

To investigate the importance of thermal FSI, we carried out this project in two steps:

• In the first simulation, we ignored the energy equation and heat transfer and focused only on the hydraulic force of the flow.

• In the second simulation, we enabled the energy equation and heat transfer so that thermal loads were also included in the FSI analysis.

Thermal Effect:

Therefore, in the thermal FSI simulation, since we intend to analyze the thermal load in addition to the overall pressure load, we need to enable the Thermal Effect option.

Why Dynamic Mesh?

Since we have been using two-way FSI, the deformed structure can affect the behavior of the fluid flowing near it. So we need to also consider the deformation of the fluid domain over time. Therefore, we used the Dynamic Mesh tool. By this, we can define the interface between the fluid and the structure for coupling purposes.

Conclusion

We have investigated the results by analyzing the interaction between fluid and solid.

Comparison:

We aim to represent a comparative analysis between the FSI due to the fluid pressure load and the FSI affected by both the pressure and thermal load.

So, we obtained the contour corresponding to the distribution of the total displacement and von Mises stress. These contours are both for the inner wall of the pipe, which is exposed to the fluid flow, and for the outer wall of the pipe, which is freely movable.

The results show that the maximum displacement appears in the bends or elbows of the pipe. This confirms that these regions undergo the highest deformation due to the fluid flowing.

In addition, the stress is considerable near bends and elbows. However, since the two ends of the pipe are considered as fixed supports, the highest stress is shown.