© fluent inc. 5/10/2015n1 fluids review trn-1998-004 postprocessing and visualization

© Fluent Inc. 04/18/23N1

Fluids ReviewTRN-1998-004

Postprocessing and Visualization



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



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 convergencetrouble affects convergence ofall 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

A

A

AA

A

A A

A AA

A

A

A

A AA

A AA

A A AA

A

A A AA

A A AA

AA

A

AA A

A

B

BB

BB

B B

B

BB B

BB

B B B BB B

B

BB

B

B B

B BB B B

B

BB

B

B

B B BB

C

C C C C C

C CC

CC C

C CC

C

C

C CC

CC

C

C C C

C

CC

CC C

C

CC C

C

C

C

D

D DD

D DD D D D

D

D DD

D

D

D

D

D D D D

D

DD

DD

D DD

DD

DD

DD

D

D

D

(X10+ 1) ITERATION NO.

NORM

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

FIDAP 7.51 7 Apr 95 14:05:53

CONVERGENCEHISTORY PLOT

REL.ERROR VEL

A - UB - VC - KD - E



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



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, ...

mo2 k



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



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, ...



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



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”



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 won’t see it!

particles released here

nothing here?! Flow structure is actually quite complex!

Particles released here



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



Histograms

Histograms are a good way to visualize distributions cell skewness other statistics (e.g., variation of density throughout flowfield)

Cell skewness distribution



2D vs. 3D

In 2D, data is normally plotted on the entire flow domain In 3D, this is not feasible — too 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



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

L

D

inm

outm fluxes: e.g., summary of mass flux in/out

of each boundary

forces: e.g., summary of xyz components of forces/moments on a surface

integrals: e.g., evaluate mass flow rate weighted average temperature at the outlet



Custom Postprocessing Values

Sometimes, the value you want to plot isn’t provided What then? Some software programs provide:

user-defined subroutines — calculation 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.



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



Animation

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

Examples: particles moving with the fluid fly-by’s, fly-through’s 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



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”

© fluent inc. 5/10/2015n1 fluids review trn-1998-004 postprocessing and visualization

Documents