Fluent Ppt 305k3

INTRODUCTION TO COMPUTATIONAL FLUID DYNAMICS

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Introduction  Fluid dynamics is a discipline that encomes a wide variety of

scientific and technical systems.  Historically, fluid dynamics analyses have been carried out by

means of analytical approximations with a narrow range of applicability and of expensive experimental studies.  The numerical integration of the fluid dynamics governing

equations allows us to solve complex flow problems with ease.  Currently, there exists both open source and commercial general-

purpose models that may deal with a wide variety of problems.  These software packages are called CFD (Computational Fluid

Dynamics) solvers and are rapidly spreading in many disciplines. 2

What is CFD?  Computational Fluid Dynamics (CFD) is the science of predicting fluid

flow, heat transfer, mass transfer, chemical reactions, and related phenomena by solving mathematical equations that represent physical laws, using a numerical process.  The result of CFD analyses is relevant engineering data:  conceptual studies of new designs  detailed product development  troubleshooting

 Redesign  CFD analysis complements testing and experimentation.  Reduces the total effort required in the laboratory. 3

Why CFD?  Experimental methods are costly  Data available throughout the domain  Scale up issues are eliminated  Complex problems can be addressed.

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CFD capabilities  Steady state and transient flows  Laminar and turbulent flows  Compressible flows  Heat transfer

 Non Newtonian flows  Variable boundary conditions  Rotating frame of reference

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Components of CFD The main stages in a CFD simulation are: 1. Preprocessing This initial step consists of defining the problem geometry, discretize it in small control volumes (mesh) and determine the suitable boundary conditions as well as initial conditions 2. Solver This step refers to the code execution and includes the monitorization of the solution.. 3. Post processing This is the final step where we analyze the results obtained from the simulation. 6

Some commercial meshing packages  Gambit  Ansys-ICEM  Hyper mesh  Pointwise  ADINA  NISA

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Some commercial CFD packages  Ansys-Fluent  CFX  Star CCM  COMSOL  FLUIDyn  ANSYS - AQWA

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Tools:  Gambit -

preprocessor To create the geometry

 Fluent -

solver manager To solve the flow equations and

post processing

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What can you do with Gambit?  Creating the geometry  Meshing the geometry  Specifying the boundary conditions  Exporting the mesh

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What can you do with FLUENT ?  Flow problems in 2D and 3D  Compressible & Incompressible  Steady state and time dependent  Variety of material properties  Complex physics & chemistry  Inviscid, viscous, and turbulence models  Multiple and non-inertial reference frames

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GAMBIT AND FLUENT

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What is Gambit?  A single, integrated preprocessor for CFD

analysis:  Geometry construction and import  Using ACIS solid modeling capabilities  Using STEP, Parasolid, IGES, etc. import  Cleanup and modification of imported data  Mesh generation for all Fluent solvers  Structured and Unstructured hexahedral, tetrahedral, pyramid, and prisms.  Mesh quality examination  Boundary zone assignment 13

Operation  General sequence of operations  Geometry Creation (ACIS, STEP, Parasolid, IGES

or Mesh import )  Create full geometry  Decompose into mesh-able sections

 Meshing  Local meshing: Edge and Boundary layers  Global meshing: Face and/or Volume  Mesh examination

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Files in Gambit 

GAMBIT directory and files 

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When GAMBIT starts up, it creates a directory called GAMBIT.#  # = the process number  It also creates a “lock” file, ident.lok, in the working directory  ident.lok prevents any from starting up another session using the same identifier in the same directory. If the code crashes, this file needs to be manually removed. Three files are created inside this directory  ident.dbs = the database. All information will be saved in this file. This file is NOT retrievable upon a  jou = crash 

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trn

=

the journal file. This file is directly accessible from the Run journal form

 Journal File:  Executable list of Gambit commands  Created automatically by Gambit from GUI and TUI.  Can be edited or created externally with text editor.  Journals are small - easy to transfer, e-mail, store

 Uses:  Can be parameterized, comments can be added  Easy recovery from a crash or power loss  edit existing commands to create new ones

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Main Menu bar

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Command line

Operation toolpad

Description window

Global Control

Vertex Edge Face Volume Group

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Boundary Layer Edge Face Volume Group

Boundary Types Boundary Entity Continuum Types Continuum Entity

Coordinate Systems Sizing Function G/Turbo -Defined Tools

Defining the Model 

Problem Identification and PreProcessing 1. Define your modeling goals. 2. Identify the domain you will model. 3. Design and create the grid

Gas Cyclon e Riser

 How will you isolate a piece

of the complete physical system?  Where will the computational domain begin and end?  Do you have boundary 19

condition information at these boundaries?

L-valve Gas

Defining the Model 

Problem Identification and PreProcessing 1. Define your modeling goals. 2. Identify the domain you will model. 3. Design and create the grid.

 What results are you looking for, and how will they

be used?  What are your modeling options?  What physical models will need to be included in your analysis?  What simplifying assumptions can you make?  Do you require a unique modeling capability?  -defined functions (written in C) in FLUENT 6

 What degree of accuracy is required? 20

 How quickly do you need the results?

Defining the Mesh 

Problem Identification and PreProcessing 1. Define your modeling goals. 2. Identify the domain you will model. 3. Design and create the grid.

triangle

quadrilateral

Can you use a quad/hex grid or should you use a tri/tet grid or hybrid grid?  How complex is the geometry and flow?  Will you need a non-conformal interface?  What degree of grid resolution is required

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tetrahedro n

hexahedro n

pyramid

prism/wedge

in each region of the domain?  Is the resolution sufficient for the geometry?  Can you predict regions with high gradients?  Will you use adaption to add resolution?  Do you have sufficient computer

Defining the solver - FLUENT 

Solver Execution 4. Set up the numerical model. 5. Compute and monitor the solution.

 For a given problem, you will need to:  Select appropriate physical models.  Turbulence, combustion, 

Solving initially in 2D will provide valuable experience with the models and solver settings for your problem in a short amount of time.

   

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

multiphase, etc. Define material properties.  Fluid  Solid  Mixture Prescribe operating conditions. Prescribe boundary conditions at all boundary zones. Provide an initial solution. Set up solver controls. Set up convergence monitors.

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Solver Execution 4. Set up the numerical model. 5. Compute and monitor the solution.

A converged and gridindependent solution on a well-posed problem will provide useful engineering results!

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

The discretized conservation equations are solved iteratively.  A number of iterations are usually required to reach a converged solution.

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Convergence is reached when:  Changes in solution variables from one iteration to the next are negligible.  Residuals provide a mechanism to help monitor this trend.  Overall property conservation is achieved.

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The accuracy of a converged solution is dependent upon:  Appropriateness and accuracy of physical models.  Grid resolution and independence  Problem setup

Visualizing the Results 

Post-Processing 6. Examine the results. 7. Consider revisions to the model.

Examine results to ensure property conservation and correct physical behavior. High residuals may be attributable to only a few cells of poor quality.

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 Examine the results to review solution and

extract useful data.  Visualization Tools can be used to answer such questions as:  What is the overall flow pattern?  Is there separation?  Where do shocks, shear layers, etc. form?  Are key flow features being resolved?  Numerical Reporting Tools can be used to calculate quantitative results:  Forces and Moments  Average heat transfer coefficients  Surface and Volume integrated quantities  Flux Balances

THANK YOU

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