Introduction To FLUENT

Introduction To FLUENT

David H. Porter Minnesota Supercomputer Institute University of Minnesota

Topics Covered in this Tutorial ●

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What you can do with FLUENT –

FLUENT is feature rich

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Summary of features and capabilities

Using FLUENT at MSI –

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Essentials of working with FLUENT –

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Hosts, X forwarding, environment, startup Basic steps for success

User Resources at MSI –

Web documentation: User Guides & tutorials

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Help is available: helpline & forums

What You Can Do With FLUENT ●

Flow problems in 2D and 3D

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Compressible & Incompressible

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Steady state and time dependent

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Variety of material properties

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Complex physics & chemsitry

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Inviscid, viscous, and turbulence models

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Complex geometries & meshes

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Multiple and non-inertial reference frames

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Quantitative analysis & visualization

Flow Problems in 2D and 3D ●

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2D –

Planar

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Axisymmetric

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Axisymmetric with swirl

3D –

Full 3D

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Complex boundaries

Compressible and Incompressible ●

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Low subsonic –

Incompressible or weakly compressible

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Constant or variable density

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Equation of state

Transonic –

Strong compressibility

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Shock waves

Supersonic & Hypersonic –

Inviscid model

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Euler discontinuities

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Strong shocks

Steady State and Time Dependent ●

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Iterative convergence to steady state solutions Follow transient solutions Use steady state solution to initialize transient problems.

Material Properties ●

Newtonian & non-Newtonian fluids

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Phase changes –

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Melting and solidification

Porous media –

Non-isotropic permeability

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Inertial resistance

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Solid heat conduction

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Porous-face pressure jump conditions

Material properties database

Porous media in a catalytic converter

Chemistry ●

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Chemical Species –

Mixing

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Reaction

Combustion models –

Homogeneous

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Heterogeneous

Surface deposition/reaction models

Complex Physics ●

MHD

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Heat transfer

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solid/fluid “conjugate” transfer

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Forced, natural & mixed convection

Volume sources of mass, momentum and energy Acoustic models: flow induced noise

000

Natural Convection Velocity field

Viscosity & Turbulence Models ●

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Models for various flow regimes –

Laminar (only for smooth flows)

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Viscous (Navier-Stokes)

Turbulence models –

Large Eddy Simulations (LES)

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Detached Eddy Simulation

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Spalart-Allmaras (1 eqn)

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K-epsilon (standard & RNG) (2 eqn)

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K-omega (2 eqn)

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Reynolds Stress (7 eqn)

Complex Geometries & Meshes ●

Various and mixed meshes –

Structured, unstructured, & mixed

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Sliding meshes

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Mixing-plane model –

Time averaged mesh boundaries

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Dynamic (deforming) meshes

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Free surfaces

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GAMBIT: mesh generation

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T-GRID: merge meshes

Reference Frames ●

Inertial –

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Stationary or moving

Non-inertial –

Rotating

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Accelerating

Multiple reference frames –

Meshes in relative motion

Quantitative Analysis ●

XY plots of values along lines –

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Primitive & derived quantities

Surface and volume integrals –

Fluxes

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Averages

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Temporal variation

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Fourier analysis

Flow Visualization ●

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On surfaces –

Contours

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Primitive and derived fields

In volumes –

Particle paths

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Vector fields

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Colored with scalar fields

Animation –

Time dependent flows

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Moving viewpoint

Using FLUENT at MSI ●

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Hardware to run FLUENT on –

Computational resources at MSI

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MSI maintains academic licenses from ANSYS

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Run locally in MSI labs

Running remotely on core hardware –

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SSH & X forwarding

Getting Started –

Environmental settings & modules

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Tutorial files & run directories

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GUIs for GAMBIT & FLUENT

FLUENT Availability at MSI ●

Core hardware (remote access) –

Altix (up to 256 processors)

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

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Labs (run locally or remotely) –

BMSDL

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SDVL http://www.msi.umn.edu/labs/

Running Remotely ●

GUI driven GAMBIT & FLUENT

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From your graphics & X11 enabled desktop –

X11 is standard with Linux shells

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

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On Windows, need X server & SSH client

X server: XMing ● SSH client: PuTTY http://www.cs.caltech.edu/courses/cs11/misc/xwindows.html ●

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Linux: SSH to remote host with X forwarding ssh -X @regatta.msi.umn.edu

Getting Started ●

Use the “fluent” module to set your environment module load fluent

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GAMBIT & FLUENT produce many files –

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Good idea to make a project directory

Tutorial resource files available on regatta –

Meshes & example output

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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

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Draw a picture with labels for consistency

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Use GAMBIT to generate mesh

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Specify geometry & boundaries

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Specify solver, mesh type & resolution

Use FLUENT to generate flow solutions –

Specify models, boundaries, material properties

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Specify solver approx, monitors, & iterate ...

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Adapt/refine mesh

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Examine/compare results

Example Problem Channel flow with backward-facing step ●

Classic problem from turbulence

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Our example: 2D for simplicity & speed

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Will solve for steady state solution

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Compare results from different models Re = (2/3)U(2h)/nu = 500

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

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

Define Geometry Y vop=(10,1)

vip=(-1,1) Wall Inflow

Wall

vi0=(-1,0) vmm=(0,-1)

vm0=(0,0) Wall

X

Wall

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

Outflow

vom=(10,-1)

Mesh Generation: Outline ●

Setup & start GAMBIT

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Specify FLUENT 5/6 solver

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0D: Vertices from point coordinates

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1D: Edges from pairs of vertexes

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2D: Domain from edges

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Specify 1D meshes on Edges

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Interior mesh (on face) from 1D meshes

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Associate boundary types & labels with edges

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Save work & export mesh

Setup GAMBIT ●

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Project Directory –

Make directory:

mkdir step

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Enter directory:

cd step

Start GAMBIT –

module load fluent

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gambit

Specify solver menu: solver -> FLUENT 5/6

Specify Vertices ●

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Vertexes from point coordinates –

Operation: GEOMETRY button

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Geometry: VETREX button

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Vertex: CREATE VERTEX button

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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

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Edge: CREATE EDGE button: strait edge (default)

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Select pairs of vertices, label, & Apply in ibot step

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{vip, vim} {vim, vm0} {vm0, vmm}

bot out top

{vmm, vom} {vom, vop} {vop, vip}

Face from edges –

Geometry: FACE button

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Face: FORM FACE button

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Select all edges, label “domain”, & Apply

Generate Mesh ●

1D Mesh on Edges (0.1 m mesh) –

Operation: MESH button

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Mesh: EDGE button

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Mesh Edges dialog: ● ●

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Spacing: 0.1 (interval size) Select all edges & Apply

Mesh 2D domain from edges –

Mesh: FACE button

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Face: MESH FACES button

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Mesh faces dialog: ● ●

Select all edges Retain defaults for quad mesh & Apply

Boundary Types ●

Associate boundary types & labels with edges –

Operation: ZONES button

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Zones: SPECIFY BOUNDARY TYPES button

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Specify Boundary Types dialog: ●

Edge, label , boundary type, in out top bot ibot step

inlet outlet top bot ibot step

VELOCITY_INLET PRESURE_OUTLET WALL WALL WALL WALL

Apply

Save Work & Export Mesh ●

Good Idea to save GAMBIT session –

Modify or fix mesh as needed

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Use as a starting point for another project Menu: File -> Save As ...

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Export mesh –

Generates a mesh file: step.msh

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

Solve for Steady State Solution ●

Use FLUENT

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Import mesh

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Models: solver, viscous, source terms, ...

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Material properties

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Boundary conditions

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Operating conditions

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Solution controls & initialization

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Monitors

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Iterate ...

Setup FLUENT ●

Use “step” project directory –

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Contains file: step.msh

Set environment: module load fluent –

Only need to do once per shell

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

Run FLUENT for 2D simulations fluent 2D

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Import mesh from file step.msh File -> Read -> Case

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Check mesh: Grid -> Check

Choose Model ●

Solver framework Define -> Models -> Solver –

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Retain defaults

Energy equation? Define -> Models -> Energy ... –

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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

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Can define your own

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Will keep default: air ●

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Dynamic Viscosity: 1.7894e-05 [kg/m-s]

Boundaries: Define -> Bounary Conditions –

Select Inlet (Velocity Inlet) & Set...

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

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Retain default settings for outlet (Pressure Outlet)

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Retain defaults for all other boundaries (Wall)

Operating Conditions & Solver Controls ●

Set operating conditions Define -> Operating Conditions ... –

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Retain defaults

NOTE: panel entry fields adapt to model chosen.

Set solver controls Solve -> Controls -> Solution ● Discretization: Momentum: 2nd order Upwind ● Retain other defaults

Initialization & Monitors ●

Initialize flow on mesh Solve -> Initialize -> Initialize ...

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Compute From: inlet

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Init

Solution convergence monitors Solve -> Monitors -> Residual ... –

Select “Plot” under Options

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Increase Storage & Plotting iterations to 10000

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Keep Continuity, X-, & Y-velocity monitors

Iterative Solution to Steady State ●

Iterate Solver -> Iterate ...

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Set # of iterations to 1000

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Iterate

Laminar: unrealistic –

Low res. mesh

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Numerical Diff.

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Need Turb. Visc.

Save settings & data File -> Write -> Case & Data ...

Try a Turbulence Model ●

Standard K-epsilon model Define -> Models -> Viscous ...

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Select k-epsilon (2 eqn)

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Retain standard default settings

Solver for SGS fields Solve -> Controls -> Solution ... –

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2nd order Upwind for TKE & TDR

Iterate ...

Examine Flow ●

Vector fields

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Contours

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Particle paths

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XY plots along lines or edges

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Quantitative reports

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Compare results from different models

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Hard copy output File -> Hardcopy ... –

I've used: JPEG & Color

Flow Visualization ●

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Display -> Vectors –

In subsets of full domain

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Colored by ...

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Zoom with middle mouse button

Display -> Contours ... –

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Select “Filled” under Options

Display -> Pathlines ... –

Steps 200; Path skip 2

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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 ... ● ●

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Plot Direction: (X,Y,Z)=(0,1,0) Surfaces: x=0.6 & Plot

Quantitative reports Report -> Fluxes ... –

Select: Inlet & Outlet

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Retain Mass Flow Rate

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Compute

Mass Flow Rate inlet outlet Net

(kg/s) 0.0029828751 -0.0029837638 -8.887e-07

Compare Results from Different Models ●

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Plot -> XY Plot ... –

Select “Write to File”

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Write

Switch cases File -> Write -> Case & Date File -> Read -> Case & Data

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Plot -> XY Plot ... –

Load File ... ●

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Select file: keps_Vx_on_x=0.6.xy

Plot

Adapt/Refine Mesh ●

Reason: test & improve accuracy

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Refinement based on your choice of

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Gradients

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Residual errors

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Domain

Adapt -> Region –

X=[-1,10]; y=[-1,1]

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Adapt ●

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doubles mesh

Solver -> Iterate ...

Comparison of Vx from 3 Models

User Resources at MSI ●

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User Guide & tutorials on the WEB: –

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

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

MSI User Support –

Email: [email protected]

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Phone: 612–626–0802 (8:30am – 5pm)

MSI web portals & Forums –

Still in planning stages

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

Proposed: MSI Forum on Fluid Dynamics/Continuum Mech. ●

Interdisciplinary & interdepartmental –

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Theory, Experiment, Computation

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Facilitate access to local resources & opportunities

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Share knowhow

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Address questions & concerns with MSI resources

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Brainstorm projects leveraged by MSI resources

Still in planning stages –

Forums will be user driven

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Your input is crucial

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Email: [email protected]