cfdb_7_postprocessing

7/27/2019 cfdb_7_postprocessing

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Fluent Inc. 6/9/2014N1

Fluids ReviewTRN-1998-004

Postprocessing and Visualization


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Outline

Solution monitoring

Solution data

Graphical display:

vectors contours

pathlines

XY plots, histograms

2D vs. 3D

Alphanumeric reports: field data, fluxes, forces, integrals

Custom Field Functions

Data export


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Solution monitoring

Graphical display of the solution provides:

quick visual check of solution status

indication of equations that are not converging

The actual solution quantity plotted depends on the software

continuity equation convergence

trouble affects convergence of

all equations Fidap example here

0.10000 0.86000 1.62000 2.38000 3.14000 3.90000

-3.07381

-2.45905

-1.84429

-1.22953

-0.61476

0.00000

LOG10**N

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(X10+ 1)ITERATION NO.

NORM

2-D TURBULENT FLOW OVER A BACKWARD-FACING STEP (SS)

FIDAP 7.517 Apr 9514:05:53

CONVERGENCEHISTORY PLOT

REL.ERROR VEL

A - UB - VC - KD - E


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Other Solution Monitors

You can also monitor and display other quantities during calculation

Value of a variable

at a boundary

at a point

Integrals/averages on a surface

Force: lift, drag, moment

Another indication of convergence

is when the monitored value stops

changing

Lift coefficient vs. iteration


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Solution Data (1)

Pressure

static, dynamic, total, pressure coefficient, ...

Velocity

magnitude, components, stream function, vorticity, helicity, ...

Temperature

static, total, enthalpy, internal energy, entropy, ...

Turbulence

kinetic energy, dissipation rate, effective viscosity, wall y+, ...

Species mass fraction, mole fraction, concentration, deposition rate, ...

r mo2

e k


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Solution Data (2)

Properties

density, viscosity, conductivity, specific heat, ...

Wall quantities

shear stress, heat flux, heat transfer coefficient, ...

Grid

coordinates, areas, volumes, quality measures, ...

Derived quantities

shear rate, stresses, other derivatives,

Custom quantites User-defined Functions

Field Function Calculator


7/18 Fluent Inc. 6/9/2014N7


Graphical Display of Data

What would colorful fluid dynamics (CFD) be without graphics?!

Graphical display should be more than just pretty pictures

The goal is visualization and understanding of the flow

capture of gross features: is the flow headed the right way

does it look correct? Have I done something wrong?

Visualization of finer features:

where does the flow separate

what does the local heat transfer coefficient look like on the wall

Many options: contours, vectors, path lines, ...


8/18 Fluent Inc. 6/9/2014N8


Contours

Color-coded contours are an effective means of visualizing scalar

quantities such as pressure, velocity magnitude, stream function,

Display is essentially 2-D

You can identify the min/max and gradients

slide coater

contours of stream function filled contours


9/18 Fluent Inc. 6/9/2014N9


Vector Plots

Velocity vectors indicate the direction and magnitude of the flow

Usually colored by velocity magnitude

Usually displayed on a surface, but shows three-dimensionality


10/18 Fluent Inc. 6/9/2014N10


Path Lines

Path lines trace the flow pattern using massless particles

3-D version of stream function contours

Can be colored/twisted by any scalar value

Be careful! You specify the starting point for the path lines, but... if the particles start outside a recirculating region, you wont see it!

particles

released

here

nothing here?! Flow structure is actually

quite complex!

Particles released here


11/18 Fluent Inc. 6/9/2014N11


XY Plots

Quantitative data can be

viewed as XY plots

Useful for comparing against

experimental or other data

Examples:

heat transfer coefficient along a

wall

pressure distribution on lift

surfaces

time dependent behavior (e.g.,

shedding)

Can be plotted on a surface, but

usually along a line

velocity distribution at exit of

a coating die


12/18 Fluent Inc. 6/9/2014N12


Histograms

Histograms are a good way to visualize distributions

cell skewness

other statistics (e.g., variation of density throughout flowfield)

Cell

skewness

distribution


13/18 Fluent Inc. 6/9/2014N13


2D vs. 3D

In 2D, data is normally plotted on the entire flow domain

In 3D, this is not feasibletoo much data!!

Thus, for 3D problems, you normally plot data on:

a surface or surfaces a line or lines

All outer boundaries are available as plotting surfaces

Most postprocessors provide tools for creating arbitrary plotting

surfaces:

points or lines planes, iso-surfaces, clipped surfaces


14/18 Fluent Inc. 6/9/2014N14


Alphanumeric Reports

It is not practical to view raw data perhaps on a small, mapped

grid

However, other alphanumeric reports are quite helpful:

udA

uTdATavg

r

r

L

D

inm

outm

fluxes: e.g., summary of mass flux in/outof each boundary

forces: e.g., summary ofxyz components

of forces/moments on a surface

integrals: e.g., evaluate mass flow rate

weighted average temperature at the outlet


15/18 Fluent Inc. 6/9/2014N15


Custom Postprocessing Values

Sometimes, the value you want to plot isnt provided

What then? Some software programs provide:

user-defined subroutinescalculation of custom quantities which then

can be visualized

field function calculator you can enter a formula in a special GUI

panel. The resulting quantity can be contoured, XY plotted, etc.


16/18 Fluent Inc. 6/9/2014N16


Data Export

Most CFD codes can write out data in other formats

For people who want to:

view the data in another CAD program (I-DEAS, PATRAN, etc.)

use a third-party postprocessor (FieldView, Ensight, Data Explorer,

Tecplot, etc.)

make some further calculations with the data using their own software


17/18 Fluent Inc. 6/9/2014N17


Animation

CFD data lends itself nicely to animation: i.e., moving pictures of the

data

Examples:

particles moving with the fluid

fly-bys, fly-throughs

visualizations of moving geometries (e.g., mixing tanks)

visualizations of other transient phenomena (e.g., movement of a shock)

data on a plane passing through the domain

Its very helpful if the CFD software provides animation support: composition of animation

proper file output formats


18/18 Fluent Inc 6/9/2014N18


Summary

Postprocessing includes all the tools needed for interpretation and

visualization of the CFD solution

Postprocessing occurs at two levels:

qualitative check: are b.c.s correct, does flow look right

extracting the quantitative results that are needed for design

2D postprocessing is fairly straightforward and trivial

Effective visualization of 3D flows is assisted by:

preparing appropriate plotting surfaces for viewing scalar data

path line plots or particle tracks to see overall flow patterns animation to bring the flow to life

cfdb_7_postprocessing

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