[ss ss17]

Hi，everyone
Recently I've been simulating fluidized beds using the TFM method, and I need to report an X-Y plot of the height of the fluidized bed layer as a function of time during fluidization, which may require the use of a UDF?

[Martin_Sz]

You're absolutely right! A User Defined Function (UDF) in Fluent can be a great way to calculate and report the time-dependent height of the fluidized bed layer during simulation using the TFM (Two-Fluid Model). Here's how you can approach this:

**UDF for Bed Height Calculation:**

1. **Identify a reference point:** You need a reference point within the bed to define the height. This could be the bottom of the bed (easy to identify) or the interface between the dense and dilute phases (more complex but potentially more accurate).

2. **Volume or Area Integration:**
* **Volume Integration:** If using the bottom of the bed as a reference, you can integrate a user-defined scalar field representing the volume fraction of the solid phase (e.g., alpha_s) across the entire height of the bed. The height will be proportional to the integral value. This approach requires defining a virtual integration box encompassing the bed.
* **Area Integration:** If using the dense-dilute interface, you can integrate the alpha_s along a user-defined surface that captures the interface between the two phases. The average height can then be calculated based on the integrated value and the area of the surface.

3. **UDF Implementation:**
* The UDF will need to access the relevant data like alpha_s, cell coordinates, and potentially other variables depending on your chosen integration method.
* The UDF will then perform the integration (volume or area) and calculate the bed height based on the chosen reference point.
* Finally, the UDF can store the calculated height in a user-defined memory (UDM) location for later reporting.

**Reporting the Bed Height:**

* You can define a report or monitor in Fluent to track the UDM location where the bed height is stored. This will provide you with the time-dependent data for the X-Y plot.

**Additional Considerations:**

* The chosen reference point (bottom vs. interface) can affect the calculated height.
* Ensure the integration method captures the desired portion of the bed accurately.
* You might need to adjust the UDF based on your specific bed geometry and simulation setup.

**Resources:**

* Fluent Documentation on UDFs: [https://www.ansys.com/training-cente...functions-udfs) (This website provides a comprehensive guide on creating and using UDFs in Fluent)
* Examples of UDFs for particle tracking and other applications can be found online, which can provide a starting point for your own UDF development.

**Remember:** UDF development requires some programming knowledge in C. If you're not comfortable with coding, consider collaborating with someone who can help you implement the UDF.

By implementing a UDF for bed height calculation and using appropriate reporting tools, you can obtain the data needed for your X-Y plot and analyze the behavior of the fluidized bed during simulation.