Udf For Fluent

Fluent Software Training UDF

User-Defined Functions in FLUENT

© Fluent Inc. 04/26/17

Fluent Software Training UDF

Agenda General Introduction to User Defined Functions(9:15) Fluent Data Structure and Macro-s(9:30) Break (10:15) Interpreted / Compiled UDF(10:30) UDF Hooks - ‘DEFINE’ macro-s(11:15) Tutorial-session-1(12:00) Lunch(12:30) User Defined Scalars and Memories(13:45) UDF for Discrete Phase Model(14:15) UDF for Multiphase Flows(14:45) Break (15:15) Tutorial-session-2(15:30) UDF for Parallel FLUENT(16:00) Miscellaneous Functions / Macros(16:30) 2

© Fluent Inc. 04/26/17

Fluent Software Training UDF

Why Build UDFs?  

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Standard interface can not be programmed to anticipate all needs Customization of boundary conditions, source terms, reaction rates (volume and surface), properties Solution initialization Adjust functions (once per iteration) Solve for user defined scalars Modify model specific parameters Many more...

Limitations 

Not all solution variables or solver models can be accessed by UDFs • Example: Cannot change specific heat (would require additional solver capabilities)

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© Fluent Inc. 04/26/17

Fluent Software Training UDF

User Access to Fluent Solver 

Fluent is so designed that the user can access the solver at some strategic instances during the solution process Segregated Solver Coupled Solver Initialize

Flow Diagram of FLUENT Solvers

Userdefined ADJUST

Begin Loop

User Defined Initialize

Solve U-Momentum Solve V-Momentum

Source terms

Exit Loop

Solve W-Momentum

Solve Mass Momentum & Energy

Source terms

Solve Mass Continuity; Update Velocity

Repeat

Solve Energy

Boxes in blue are some important user access points

Solve Species Check Convergence

Solve Turbulence Kinetic Energy

Update Properties

Source terms

Solve Eddy Dissipation

User-Defined Properties User-Defined Boundary Conditions 4

© Fluent Inc. 04/26/17

Fluent Software Training UDF

User Defined Functions in Fluent 

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User Defined Functions are not just any C-functions:  User access needs specific “Type” of function calls  These Function types or ‘macro’-s are defined in the header file: ~Fluent.Inc/fluentx.y/src/udf.h

UDF’s in FLUENT are available for: 

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Profiles (Boundary Conditions) velocity, temperature, turbulence, species, scalars Source terms (Fluid and solid zones) mass, momentum, energy, species, turbulence, scalars Properties viscosity, conductivity, density, scattering_phase_function (except specific heat) 5

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Initialization zone and variable specific initialization Global Functions adjust, read, write, execute_on_demand Scalar Functions unsteady term, flux vector, diffusivity Model Specific Functions reaction rates, discrete phase model, turbulent viscosity © Fluent Inc. 04/26/17