T-junction, Thermal FSI, ANSYS Fluent CFD Simulation

Description

In this project, we present a simulation of a T-junction Pipe under Thermal FSI via ANSYS Fluent software. We have modeled a simple T-junction containing a main pipe and a branch, so that two streams with different temperatures would be mixed. The computational domain consists of a fluid zone dedicated to the streams and a solid region as the pipe body surrounding the fluid zone.

What is FSI?

Two fluid streams flow through the T-junction pipe. So, the fluid flow can expose a pressure load on the inner wall of the T-junction pipe. 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?

Two streams with different temperatures flow throughout the T-junction. 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 T-junction pipe is analyzed. Next, the effect of the solid T-junction 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.

Thermal Effect:

Since we intend to analyze the thermal load in addition to the overall pressure load, we 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.

Structural:

We obtained the contours related to the distribution of the total displacement and von Mises stress on the T-junction structure body (both for the inner wall of the pipe, which is exposed to the fluid flow, and for the outer wall, which is freely movable.

The results confirm that the maximum displacement appears in the T-junction zone, between the fixed support at the end of each branch. It means that T-junction regions undergo the highest deformation due to the fluid flowing.

On the other hand, the stress reaches its highest value at the adjacent to each support. In addition, the branch containing the hotter fluid shows a higher stress, which could be due to the effect of thermal stress.