💥💥💥 What is loosely coupled conjugate heat transfer in Ansys Fluent?

 Loosely coupled conjugate heat transfer (CHT) is a new feature in Ansys Fluent 2021R1 that allows you to simulate heat transfer between fluid and solid domains without requiring a conformal mesh or a coupled solver. With this approach, the coupled fluid/solid interface is replaced by boundary conditions: the temperature boundary condition from the solid zones is assigned to the fluid domain, while the heat flux boundary condition from the fluid zones are assigned to the solid domain. This way, you can use different time steps and solvers for the fluid and solid regions, and exchange information between them at a specified coupling frequency. This can reduce the computational cost and complexity of CHT simulations, especially for transient problems with large temperature gradients and deformations. You can learn more about this feature from the following sources:

• How does the “Loosely Coupled Conjugate Heat Transfer” function work? - Ansys Learning Forum
• Fluent Loosely Coupled Conjugate Heat Transfer - Ansys Learning Forum
• CHT Analysis in Ansys Discovery | Ansys Courses
• Ansys Fluent Heat Transfer Modeling | Ansys Training
• Fast Conjugate Heat Transfer Simulation of Long Transient Flexible …

What is the difference between loosely coupled and tightly coupled CHT?

The difference between loosely coupled and tightly coupled CHT is the degree of dependency between the fluid and solid domains in the simulation. In loosely coupled CHT, the fluid and solid domains are solved separately using different meshes, time steps, and solvers, and the information is exchanged between them at a specified frequency. This reduces the computational cost and complexity of the simulation, but may introduce some errors due to interpolation and synchronization. In tightly coupled CHT, the fluid and solid domains are solved simultaneously using a conformal mesh and a coupled solver. This ensures accuracy and stability of the solution, but may increase the computational time and memory requirements. You can find more details about these two approaches from the web search results I found for you¹²³⁴⁵.

How do I choose between loosely coupled and tightly coupled CHT for my simulation?

The choice between loosely coupled and tightly coupled CHT depends on the characteristics of your simulation problem and the trade-off between accuracy and efficiency. Some factors that may influence your decision are:

• The size and complexity of your model: loosely coupled CHT can handle larger and more complex models with less computational resources, while tightly coupled CHT may require more memory and CPU time.
• The type and quality of your mesh: loosely coupled CHT can work with non-conformal meshes that have gaps or overlaps between the fluid and solid domains, while tightly coupled CHT requires a conformal mesh that matches the interface exactly.
• The magnitude and variation of the temperature and heat flux at the interface: loosely coupled CHT may introduce some errors due to interpolation and synchronization of the boundary conditions, while tightly coupled CHT ensures accuracy and stability of the solution.
• The transient behavior and deformation of the fluid and solid domains: loosely coupled CHT can handle large deformations and long transient simulations with different time steps for the fluid and solid domains, while tightly coupled CHT may require smaller time steps and more iterations to converge.

You can find more information about these factors from the web search results I found for you . You can also try both approaches and compare the results to see which one suits your needs better.

How to define loosely coupled conjugate heat transfer model in Ansys Fluent ?

To define a loosely coupled conjugate heat transfer model in Ansys Fluent, you need to follow these steps:

• Create a non-conformal mesh for the fluid and solid domains, or import an existing mesh from another software. You can use different element types and sizes for the fluid and solid regions, as long as they are compatible with Fluent.
• In the Fluent interface, go to the Setup panel and enable the Loosely Coupled Conjugate Heat Transfer option under Models > Energy.
• Specify the fluid time step size and the solid time step size under Solution > Methods. The fluid time step size should be smaller than the solid time step size to ensure accuracy and stability.
• Specify the coupling frequency under Solution > Loosely Coupled CHT. The coupling frequency determines how often the information is exchanged between the fluid and solid domains. You can choose to couple every N fluid time steps, or every N seconds of physical time.
• Define the material properties and boundary conditions for the fluid and solid zones under Materials and Boundary Conditions. For the fluid/solid interface, you need to select the Loosely Coupled CHT boundary condition type and assign the appropriate zones as source and target. Fluent will automatically interpolate the temperature and heat flux values from the adjacent zones using a conservative scheme.
• Initialize the solution and run the calculation under Solution > Initialization and Solution > Run Calculation. You can monitor the convergence and results under Solution > Monitors and Results.

You can find more details and examples about this feature from the web search results I found for you¹²³⁴. I hope this helps you with your simulation. 😊

How do I post-process my CHT simulation results in Fluent?

To post-process your CHT simulation results in Fluent, you can use the tools available in the Results tab of Fluent. You can create various surfaces and graphics objects to visualize the temperature and heat flux distributions in the fluid and solid domains. You can also extract numerical results using surface integrals, fluxes, and XY plots. You can find some tutorials and examples on how to do post-processing in Fluent from the web search results I found for you¹²³⁴⁵. Here are some steps you can follow to post-process your CHT simulation results in Fluent:

• In the Results tab, go to Surfaces and create a plane surface that cuts through the fluid/solid interface. You can use the Define Plane by 3 Points option and select three points on the interface to define the plane.
• In the Graphics and Animations panel, go to Contours and select Temperature as the variable to display. Select the plane surface you created as the surface to display on. Click Display to see the temperature distribution on the plane.
• In the Graphics and Animations panel, go to Vectors and select Velocity as the variable to display. Select the plane surface you created as the surface to display on. Click Display to see the velocity vectors on the plane.
• In the Graphics and Animations panel, go to Pathlines and select Temperature as the variable to color by. Select a point or a line on the inlet or outlet of the fluid domain as the starting location for the pathlines. Click Display to see the pathlines of fluid particles colored by temperature.
• In the Reports panel, go to Surface Integrals and select Heat Flux as the variable to report. Select a surface or a group of surfaces on the fluid/solid interface as the surface to report on. Click Compute to see the total heat flux across the interface.
• In the Reports panel, go to Fluxes and select Mass Flow Rate as the variable to report. Select a surface or a group of surfaces on the inlet or outlet of the fluid domain as the surface to report on. Click Compute to see the mass flow rate through the surface.
• In the Reports panel, go to XY Plot and select Temperature as the Y variable and X Coordinate as the X variable. Select a line or a point on the fluid/solid interface as the surface to plot on. Click Plot to see a graph of temperature versus x coordinate along the interface.

You can also create scenes to combine multiple graphics objects in a single display, or export images or data files for further analysis. I hope this helps you with your post-processing. 😊