# How to Implement Fluid Recycling with Specific Recycle Ratio in CFD Simulation using MATLAB

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Desta Sodano on 1 Apr 2024
Answered: Kothuri on 24 May 2024
Could someone please guide me on implementing fluid recycling from outlet to inlet with a prescribed recycle ratio using MATLAB for pre-processing and post-processing, and ANSYS Fluent for the simulation? Specifically, I need assistance with setting up boundary conditions, defining the recycling inlet, and ensuring the prescribed recycle ratio is achieved in the simulation.

Kothuri on 24 May 2024
Hi,
I understand that you want to Implement Fluid Recycling with Specific Recycle Ratio in CFD Simulation using MATLAB for pre-processing and post-processing, and ANSYS Fluent for the simulation.
MATLAB can be used for pre-processing and post-processing tasks.
• Do the Simulation Setup in ANSYS Fluent and ensure your computational domain accurately represents the physical system. The geometry does not necessarily need to include the physical recycle loop but should allow for the simulation of recycling flow dynamics.
• Setup the boundary conditions of inlets, outlet such as fresh flow, recycled flow, outflow etc.
• Calculate the portion of the outlet flow to be reintroduced into the system based on your recycle ratio. This might involve using a UDF (User-Defined Function) to dynamically adjust the flow based on simulation results.
• Write a UDF to dynamically adjust the mass flow rate at the recycling inlet based on the outlet flow and the desired recycle ratio.
• The UDF can fetch the outlet mass flow rate, calculate the required recycled flow, and adjust the inlet boundary condition accordingly.
• Start the simulation with an initial guess for the recycled flow. This might be based on steady-state assumptions or a previous time step if running a transient simulation.
• Allow the simulation to iterate until it reaches a steady state or completes the defined time steps for a transient analysis. Monitor the mass flow rates to ensure the recycle ratio is achieved.
• Use MATLAB to calculate initial estimates for your boundary conditions based on the prescribed recycle ratio.
• MATLAB can also be used to automate the generation of input files for ANSYS Fluent.
• Use ANSYS Fluent to export the necessary simulation data, such as outlet mass flow rates, inlet conditions, and any other relevant parameters.
• Import this data into MATLAB to calculate the actual recycle ratio achieved in the simulation, compare it with the prescribed value, and perform any additional analysis required for your study.
You can refer the below link for information on interaction between MATLAB and ANSYS