Tri/Tet vs. Quad/Hex Meshes

rangebeaverMechanics

Feb 22, 2014 (3 years and 3 months ago)

81 views

لدم
k
-
ε

Standard
k
-


Model

ايازم
:

دريگ يم رارق هدافتسا دروم تعنص رد یا هدرتسگ روطب
.

تسا هدش رشتنم لدم نيا راتفر نوماريپ یدايز رايسب دانسا و تلااقم
.

تسا قداص هتفشآ هتفاي هعسوت نايرج یارب لدم نيا
.

ترارح لاقتنا و لايس نايرج زا مئا يسدنهم لئاسم زا یرايسب یارب
دراد يلوبق لباق تقد
.

بياعم

تسا نيياپ شور نيا تقد ،دنراد دايز انحنا هک يياه هسدنه یارب
.

قيقد شور نيا زين دايز رايسب راسف تفا ،هديچيپ رايسب لئاسم رد
تسين
.


لايس صاوخ نداد



درکراک طئارش


-

راشف فيرعت

-
هبذاج باتش فيرعت

تنئولف یاه تيلباق


يزرم طئارش فيرعت



یدورو تعرس يزرم طرش
Velocity
Inlets


رد تعرس رادرب فيرعت
دورو



تعرس رادرب هک يتقو يارب
لباق ،دشاب يم مولعم يدورو
تسا هدافتسا
.



لباق تخاونکي یدورو تعرس ليفورپ یارب
زا دياب تروصنيا ريغ رد ،تسا هدافتسا
UDF


درک هدافتسا
.


داجيا ثعاب مکارت لباق ريغ نايرج تلاح رد
دوش يم يکيزيف ريغ طئاش
.


يزرم طرش هک دينک يعس
عنام یکيدزن رد تعرس
دشابن یدورو
.

یدورو تعرس يزرم طرش

يگتفشآ يزرم طئارش ندرک دراو


دوجو يزرم طرش نداد یارب شور راهچ
دراد
:


نييعت
k

و



2
U
1
.
0
k

يگتفشآ يزرم طئارش ندرک دراو


دوجو يزرم طرش نداد یارب شور راهچ
دراد
:


يگتفشآ تدش و یگتفشآ يلوط سايقم نييعت
Set turbulence intensity and
turbulence length scale


نيبروت زا يجورخ
Exhaust of a turbine



Intensity
(
يگتفشآ تدش
)
=
20
%

Length scale
(
يلوط سا
ِ
فم
)

=
1
-

10
% of blade
span



لاناک کي زا يجورخ هتفاي هعسوت لامک نايرج
Fully
-
developed flow in a duct or pipe

Intensity
(
يگتفشآ تدش
)

=
5
%


Length scale
(
يلوط سا
ِ
فم
)

= hydraulic
diameter

يگتفشآ يزرم طئارش ندرک دراو


دوجو يزرم طرش نداد یارب شور راهچ
دراد
:


یگتفشآ تجزل تبسن و یگتفشآ تدش نييعت

)
Set turbulence intensity and
turbulent viscosity ratio
(

يگتفشآ يزرم طئارش ندرک دراو


دوجو يزرم طرش نداد یارب شور راهچ
دراد
:


یکيلورديه رطق و يگتفشآ تدش نييعت
(
Set
turbulence intensity and hydraulic
diameter
)

یدورو يزرم طرش
-

راشف


رلاکسا یاهرتماراپ رياس ،يلک يامد ،يلک راشف فيرعت





)
1
/(
2
)
2
1
1
(




k
k
static
total
M
k
p
p
2
2
1
v
p
p
static
total



incompressible flows

compressible flows

یدورو يزرم طرش
-

راشف


یدورو تهج فيرعت


حطس رب دمع


تهج رکد






يجورخ يزرم طرش
-

راشف


يکيتاتسورديه راشف رادقم فيرعت


تسدب يباي نورب قيرط زا جورخ رد يکيتاتسورديه راشف رادقم ،توص قوفام نايرج تلاح رد
ديآ يم

یدورو يزرم طرش
-

يمرج يبد


يمرج يبد رادقم فيرعت


راشف رادقم ،توص قوفام نايرج تلاح رد
نورب قيرط زا جورخ رد يکيتاتسورديه
ديآ يم تسدب يباي


یدورو لايس تهج


نايرج هب طوبرم یاهرتماراپ رياس

هتفشآ


راويد یزرم طرش
(
نکاس راويد
)


-

شزغل مدع طرش

(No Slip)


-

راويد یور رب لايس يشرب شنت نييعت




راويد یزرم طرش
(
کرحتم راويد
)


-

لاقتنا

-

نارود

-
تعرس ياه هفلوم نييعت





یزرم طرش


راويد يترارح


-

ييامرگ راش


-

امد

-
يياجباج





یزرم طرش


راويد يترارح


-

ييامرگ راش

-

امد

-
يياجباج





یزرم طرش


راويد يترارح


-

ييامرگ راش

-

امد

-
يياجباج





راويد سنج باختنا


-

دشاب يم مينيمولآ راويد یارب تنئولف ضرف شيپ
.
ريز لکش هب راويد صاوخ هيقب ندرک لاعف یارب
مينک يم لمع
:





Tri/Tet vs. Quad/Hex Meshes


For
simple

geometries, quad/hex
meshes can provide high
-
quality
solutions with fewer cells than a
comparable tri/tet mesh.




For
complex

geometries, quad/hex
meshes show no numerical
advantage, and you can save
meshing effort by using a tri/tet
mesh.


Hybrid Mesh Example


Valve port grid


Specific regions can
be meshed with
different cell types.


Both efficiency and
accuracy are
enhanced relative
to a hexahedral or
tetrahedral mesh
alone.


Tools for hybrid
mesh generation
are available in
Gambit and TGrid.

Hybrid mesh for an
IC engine valve port

tet mesh

hex
mesh

wedge mesh

Non
-
Conformal Mesh Example


Nonconformal mesh:

mesh in which grid nodes do not match up along an interface.


Useful for ‘parts
-
swapping’ for design study, etc.


Helpful for meshing complex geometries.


Example:


3
D Film Cooling Problem


Coolant is injected into a duct

from a plenum


Plenum is meshed with

tetrahedral cells.


Duct is meshed with

hexahedral cells.

Plenum part can be replaced with new
geometry with reduced meshing
effort.

Set Up the Numerical Model


For a given problem, you will need to:


Select appropriate physical models.


Turbulence, combustion, 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.

Compute the Solution


The discretized conservation equations are solved
iteratively
.


A number of iterations are usually required to reach a
converged solution.


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.


The accuracy of a converged solution is dependent upon:


Appropriateness and accuracy of the physical models.


Grid resolution and independence


Problem setup


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


Examine the Results


Examine the results to review solution and to extract useful
engineering data.


Visualization 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?


Are physical models and boundary conditions appropriate?


Are there local convergence problems?


Numerical reporting tools can be used to calculate quantitative
results:


Lift and drag


Average heat transfer coefficients


Surface
-
averaged quantities

Tools to Examine the Results


Graphical tools


Grid, contour, and vector plots


Pathline and particle trajectory plots


XY plots


Animations


Numerical reporting tools


Flux balances


Surface and volume integrals and averages


Forces and moments

Consider Revisions to the Model


Are physical models appropriate?


Is flow turbulent?


Is flow unsteady?


Are there compressibility effects?


Are there
3
D effects?


Are boundary conditions correct?


Is the computational domain large enough?


Are boundary conditions appropriate?


Are boundary values reasonable?


Is grid adequate?


Can grid be adapted to improve results?


Does solution change significantly with adaption, or is the
solution grid independent?


Does boundary resolution need to be improved?

Review for Demo


Problem Identification and Pre
-
Processing


1
.
Define your modeling goals.


2
.
Identify the domain you will model.


3
.
Design and create the grid.


Solver Execution


4
.
Set up the numerical model.


5
.
Compute and monitor the solution.


Post
-
Processing


6
.
Examine the results.


7
.
Consider revisions to the model.

FLUENT DEMO


Startup Gambit


load database


define boundary zones


export mesh


Startup Fluent


GUI


Problem Setup


Solve


Post
-
Processing

Operating System Basics: Unix


Basic Unix commands:


pwd

-

prints the name current working directory


Your home directory is home/fluent/.


ls

-

lists the files in the current directory


cd

-

change working directories (
cd ..

to go up one
directory).


The environment variable $TRAINPATH contains a shortcut to
the directory where training files are stored. For example:


cp $TRAINPATH/fluent
5
.x/tut/elbow/elbow.msh
.


will copy the mesh file for the first example problem into your
current working directory.


To start Fluent
5
:


% fluent
2
d &


To start Fluent
4.5
:


% fluent
-
r
4.5
&

Operating System Basics: Windows NT


PC users will find tutorials under
c:
\
Fluent.Inc
\
fluent
5
.x
\

tut
\
.

This directory is write
-
protected.


Save files to your home directory,
c:
\
users
\
fluent
\
.


Fluent can be started from the command prompt or from the start
menu:


Command Prompt


fluent
2
d


Start Menu


Start



Programs



Fluent Inc



Fluent
5
.x



!Note: It is recommended that you restart Fluent for each tutorial for
both
Unix and NT

systems to avoid mixing solver settings from
different tutorials.