Introduction To FLUENT

David H. PorterMinnesota Supercomputer Institute

University of Minnesota

Topics Covered in this Tutorial

● What you can do with FLUENT– FLUENT is feature rich

– Summary of features and capabilities

● Using FLUENT at MSI– Hosts, X forwarding, environment, startup

● Essentials of working with FLUENT– Basic steps for success

● User Resources at MSI – Web documentation: User Guides & tutorials

– Help is available: helpline & forums

What You Can Do With FLUENT

● Flow problems in 2D and 3D● Compressible & Incompressible● Steady state and time dependent● Variety of material properties● Complex physics & chemsitry● Inviscid, viscous, and turbulence models● Complex geometries & meshes● Multiple and non-inertial reference frames● Quantitative analysis & visualization

Flow Problems in 2D and 3D

● 2D– Planar

– Axisymmetric

– Axisymmetric with swirl

● 3D– Full 3D

– Complex boundaries

Compressible and Incompressible ● Low subsonic

– Incompressible or weakly compressible

– Constant or variable density

– Equation of state

● Transonic– Strong compressibility

– Shock waves

● Supersonic & Hypersonic– Inviscid model

– Euler discontinuities

– Strong shocks

Steady State and Time Dependent

● Iterative convergence to steady state solutions

● Follow transient solutions

● Use steady state solution to initialize transient problems.

Material Properties● Newtonian & non-Newtonian fluids● Phase changes

– Melting and solidification

● Porous media– Non-isotropic permeability

– Inertial resistance

– Solid heat conduction

– Porous-face pressure jump conditions

● Material properties database

Porous media in a catalytic converter

Chemistry

● Chemical Species– Mixing

– Reaction

● Combustion models– Homogeneous

– Heterogeneous

● Surface deposition/reaction models

Complex Physics

● MHD

● Heat transfer– solid/fluid “conjugate” transfer

– Forced, natural & mixed convection

● Volume sources of mass, momentum and energy

● Acoustic models: flow induced noise

000

Natural ConvectionVelocity field

Viscosity & Turbulence Models● Models for various flow regimes

– Laminar (only for smooth flows)

– Viscous (Navier-Stokes)

● Turbulence models– Large Eddy Simulations (LES)

– Detached Eddy Simulation

– Spalart-Allmaras (1 eqn)

– K-epsilon (standard & RNG) (2 eqn)

– K-omega (2 eqn)

– Reynolds Stress (7 eqn)

Complex Geometries & Meshes

● Various and mixed meshes– Structured, unstructured, & mixed

● Sliding meshes● Mixing-plane model

– Time averaged mesh boundaries

● Dynamic (deforming) meshes● Free surfaces● GAMBIT: mesh generation● T-GRID: merge meshes

Reference Frames● Inertial

– Stationary or moving

● Non-inertial– Rotating

– Accelerating

● Multiple reference frames– Meshes in relative motion

Quantitative Analysis

● XY plots of values along lines– Primitive & derived

quantities

● Surface and volume integrals– Fluxes

– Averages

● Temporal variation● Fourier analysis

Flow Visualization

● On surfaces– Contours

– Primitive and derived fields

● In volumes– Particle paths

– Vector fields

– Colored with scalar fields

● Animation– Time dependent flows

– Moving viewpoint

Using FLUENT at MSI● Hardware to run FLUENT on

– Computational resources at MSI

– MSI maintains academic licenses from ANSYS

– Run locally in MSI labs

● Running remotely on core hardware– SSH & X forwarding

● Getting Started– Environmental settings & modules

– Tutorial files & run directories

– GUIs for GAMBIT & FLUENT

FLUENT Availability at MSI

● Core hardware (remote access)– Altix (up to 256 processors)

– Regatta (up to 32 processors)http://www.msi.umn.edu/hardware/

● Labs (run locally or remotely)– BMSDL

– SDVLhttp://www.msi.umn.edu/labs/

Running Remotely

● GUI driven GAMBIT & FLUENT● From your graphics & X11 enabled desktop

– X11 is standard with Linux shells

– On Mac use an xterm shell & “ssh -Y ...”

– On Windows, need X server & SSH client● X server: XMing● SSH client: PuTTY

http://www.cs.caltech.edu/courses/cs11/misc/xwindows.html

● Linux: SSH to remote host with X forwarding

ssh -X <user_name>@regatta.msi.umn.edu

Getting Started● Use the “fluent” module to set your environment

module load fluent

● GAMBIT & FLUENT produce many files– Good idea to make a project directory

● Tutorial resource files available on regatta– Meshes & example output

– Zipped files for each tutorial/usr/local/Fluent.Inc/fluent6.3.26/help/tutfiles

http://wwwr.msi.umn.edu/fluent/tutfiles/

Essentials of Working with FLUENT

● Dream up a problem● Draw a picture with labels for consistency● Use GAMBIT to generate mesh

– Specify geometry & boundaries

– Specify solver, mesh type & resolution

● Use FLUENT to generate flow solutions– Specify models, boundaries, material properties

– Specify solver approx, monitors, & iterate ...

– Adapt/refine mesh

– Examine/compare results

Example Problem

Channel flow with backward-facing step● Classic problem from turbulence● Our example: 2D for simplicity & speed● Will solve for steady state solution● Compare results from different models

Rani, Sheu, & Tsai, 2007,JFM vol. 588, pp. 43–58

Lambros, Kaiktsis, Karniadakis, & Orszag, 1991JFM vol. 231, pp. 501-528

Re = (2/3)U(2h)/nu = 500

Define Geometry

X

Y

vip=(-1,1)

vi0=(-1,0)

vop=(10,1)

vom=(10,-1)vmm=(0,-1)

vm0=(0,0)Inflow

Outflow

WallWall

Wall

Wall

●2D problem: Z=0●Walls can be free slip or no slip●Use default MKS units

Mesh Generation: Outline● Setup & start GAMBIT● Specify FLUENT 5/6 solver● 0D: Vertices from point coordinates● 1D: Edges from pairs of vertexes● 2D: Domain from edges● Specify 1D meshes on Edges● Interior mesh (on face) from 1D meshes● Associate boundary types & labels with edges● Save work & export mesh

Setup GAMBIT● Project Directory

– Make directory: mkdir step

– Enter directory: cd step

● Start GAMBIT– module load fluent

– gambit

● Specify solver

menu: solver -> FLUENT 5/6

Specify Vertices

● Vertexes from point coordinates– Operation: GEOMETRY button

– Geometry: VETREX button

– Vertex: CREATE VERTEX button

– Enter coordinates with labels & APPLY for each pair

vip (-1,1) vmm (0,-1)

vim (-1,0) vom (10,-1)

vm0 (0,0) vop (10,1)

● Resize view to see all– Global Control: FIT TO WINDOW button

Create 1D Edges & 2D Domain● Edges from pairs of vertices

– Geometry: EDGE button

– Edge: CREATE EDGE button: strait edge (default)

– Select pairs of vertices, label, & Applyin {vip, vim} bot {vmm, vom}

ibot {vim, vm0} out {vom, vop}

step {vm0, vmm} top {vop, vip}

● Face from edges– Geometry: FACE button

– Face: FORM FACE button

– Select all edges, label “domain”, & Apply

Generate Mesh● 1D Mesh on Edges (0.1 m mesh)

– Operation: MESH button

– Mesh: EDGE button

– Mesh Edges dialog:● Spacing: 0.1 (interval size)● Select all edges & Apply

● Mesh 2D domain from edges – Mesh: FACE button

– Face: MESH FACES button

– Mesh faces dialog:● Select all edges● Retain defaults for quad mesh & Apply

Boundary Types● Associate boundary types &

labels with edges– Operation: ZONES button

– Zones: SPECIFY BOUNDARY TYPES button

– Specify Boundary Types dialog:● Edge, label , boundary type, Apply

in inlet VELOCITY_INLET

out outlet PRESURE_OUTLETtop top WALL

bot bot WALL

ibot ibot WALL

step step WALL

Save Work & Export Mesh● Good Idea to save GAMBIT session

– Modify or fix mesh as needed

– Use as a starting point for another projectMenu: File -> Save As ...

● Export mesh– Generates a mesh file: step.msh

– Will import this file into FLUENTMenu: File -> Export -> Mesh ...● Enable “Export 2-D (X-Y) Mesh”● File name: step.msh● Accept

Solve for Steady State Solution

● Use FLUENT● Import mesh● Models: solver, viscous, source terms, ...● Material properties● Boundary conditions● Operating conditions● Solution controls & initialization● Monitors● Iterate ...

Setup FLUENT● Use “step” project directory

– Contains file: step.msh

● Set environment: module load fluent– Only need to do once per shell

– Can put “module load ...” in file: .bashrc

● Run FLUENT for 2D simulations

fluent 2D

● Import mesh from file step.msh

File -> Read -> Case

● Check mesh: Grid -> Check

Choose Model● Solver framework

Define -> Models -> Solver

– Retain defaults

● Energy equation?

Define -> Models -> Energy ...

– Simple, low Mach flow: Try energy eqn. off

● Viscosity model

Define -> Models -> Viscous ...

– Try Laminar option.

Materials & Boundaries

● Select fluid

Define -> Materials ...

– Can select from Database

– Can define your own

– Will keep default: air● Dynamic Viscosity: 1.7894e-05 [kg/m-s]

● Boundaries: Define -> Bounary Conditions– Select Inlet (Velocity Inlet) & Set...

– Set Velocity Magnitude: 0.002435 m/s (Re ~ 500)

– Retain default settings for outlet (Pressure Outlet)

– Retain defaults for all other boundaries (Wall)

Operating Conditions & Solver Controls● Set operating conditions

Define -> Operating Conditions ...

– Retain defaults

● NOTE: panel entry fields adapt to model chosen.

Set solver controlsSolve -> Controls -> Solution● Discretization: Momentum: 2nd order

Upwind● Retain other defaults

Initialization & Monitors● Initialize flow on mesh

Solve -> Initialize -> Initialize ...

– Compute From: inlet

– Init

● Solution convergence monitors

Solve -> Monitors -> Residual ...

– Select “Plot” under Options

– Increase Storage & Plotting iterations to 10000

– Keep Continuity, X-, & Y-velocity monitors

Iterative Solution to Steady State● Iterate

Solver -> Iterate ...

– Set # of iterations to 1000

– Iterate

● Laminar: unrealistic– Low res. mesh

– Numerical Diff.

– Need Turb. Visc.

● Save settings & data

File -> Write -> Case & Data ...

Try a Turbulence Model● Standard K-epsilon model

Define -> Models -> Viscous ...

– Select k-epsilon (2 eqn)

– Retain standard default settings

● Solver for SGS fields

Solve -> Controls -> Solution ...

– 2nd order Upwind for TKE & TDR

● Iterate ...

Examine Flow● Vector fields● Contours● Particle paths● XY plots along lines or edges● Quantitative reports● Compare results from different models● Hard copy output

File -> Hardcopy ...

– I've used: JPEG & Color

Flow Visualization● Display -> Vectors

– In subsets of full domain

– Colored by ...

– Zoom with middle mouse button

● Display -> Contours ...– Select “Filled” under Options

● Display -> Pathlines ...– Steps 200; Path skip 2

– Release from “default-interior”

Quantitative Results● Pressure along a vertical cut

Surface -> Line/Rake● X0=X1=0.6; Y0=-1; Y1=1● Name: x=0.6

Plot -> XY Plot ...● Plot Direction: (X,Y,Z)=(0,1,0)● Surfaces: x=0.6 & Plot

● Quantitative reports

Report -> Fluxes ...

– Select: Inlet & Outlet

– Retain Mass Flow Rate

– Compute

Mass Flow Rate (kg/s)inlet 0.0029828751outlet -0.0029837638Net -8.887e-07

Compare Results from Different Models

● Plot -> XY Plot ...– Select “Write to File”

– Write

● Switch cases

File -> Write -> Case & Date

File -> Read -> Case & Data

● Plot -> XY Plot ...– Load File ...

● Select file: keps_Vx_on_x=0.6.xy

– Plot

Adapt/Refine Mesh

● Reason: test & improve accuracy● Refinement based on your choice of

– Gradients

– Residual errors

– Domain

● Adapt -> Region– X=[-1,10]; y=[-1,1]

– Adapt● doubles mesh

● Solver -> Iterate ...

Comparison of Vx from 3 Models

User Resources at MSI● User Guide & tutorials on the WEB:

– GAMBIT: http://wwwr.msi.umn.edu/gambit/index.htm

– FLUENT: http://wwwr.msi.umn.edu/fluent/index.htm

● MSI User Support– Email: help@msi.umn.edu

– Phone: 612–626–0802 (8:30am – 5pm)

● MSI web portals & Forums– Still in planning stages

– Will be under MSI web site http://www.msi.umn.edu

Proposed:MSI Forum on Fluid Dynamics/Continuum Mech.

● Interdisciplinary & interdepartmental– Theory, Experiment, Computation

– Facilitate access to local resources & opportunities

– Share knowhow

– Address questions & concerns with MSI resources

– Brainstorm projects leveraged by MSI resources

● Still in planning stages– Forums will be user driven

– Your input is crucial

– Email: porter@msi.umn.edu