CFD preprocessing ansys Tute

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MEC330/6016 Fluids - CFD Tutorial

Introduction

This document contains a step-by-step guide to simulate flow in a generic conical diffuser.

The guide is based on ANSYS 16.x and it is divided in four parts: geometry creation,

meshing, Fluent analysis, and post-processing.

Starting up Ansys Workbench

ClickStart menu / All Programs / ANSYS 16.x / Workbench 16.x

Geometry

Uniform inlet conditions along with the diffuser geometry allow to perform a 2D-axisymmetric

simulation. The inlet and outlet diameters are d = 89 mmand D = 140 mm, respectively.

Activate the Design Modeler

1. Drag Geometryfrom the left Component Systemslist into the right Project Schematic

workspace

2. R-click on Geometry/ Properties

3. select 2D inAnalysis Typelist.

Diameter - change in ANSYS


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Sketch the geometry

R-click on Geometry / New DesignModeler Geometry...A new Design Modeler(DM)

window will open

select Units / Millimeterin the toolbar

in the left Tree Outline, select XYPlane , then click NewSketch

in the Toolbar

click ZAxis in Model View

select Sketch1underXYPlane, click Sketching in Tree Outlinewindow, click

Constraints, scroll down and selectAuto Constraints check both Globaland Cursor

select Sketch1 under XYPlane in Tree Outline, click Sketching in Sketching

Toolboxeswindow

select Draw click Linetool.

In Graphics window:

click along the vertical YAxis

draw the inlet wall horizontal to the XAxis

click Dimensions in Sketching Toolboxes and select General

click on the drawn line, hold the left mouse button and move a short vertical distance

away from the original position

set H1to 3d = 267 mm in the Details Viewwindow.

To draw the cone section wall: Click Draw in Sketching Toolboxes, select Linetool

in the Graphics window, click on the right end of the inlet pipe wall and draw an

inclined line

ClickAngle in Dimensionstoolbox

ctrl + left clickon the diffuser wall line, hold ctrland click the inlet pipe wall

move a bit the mouse to show the angle if it is not as in the figure, right clickand

select Alternate Angle

set 170 in Details View (in this case, the cone angle is 20).

Finish the geometry: draw outlet walland set its length to 5D = 700 mm

draw inlet line (along YAxis) with length 0.5*d = 44.5 mm

draw outlet line (parallel to the inlet line and perpendicular to the outlet wall) with

length 0.5*D = 70 mm

draw axis line alongXAxis.

Create the Surface

Click Modeling in Sketching Toolboxes, select Sketch1

click Concept in the tool bar select Surfaces From Sketches


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clickApply in Details View

click .

Partition the Solution Domain In the left Tree Outline, select XYPlane , then click NewSketchin the Toolbar

select Sketch2and click Sketching

draw a vertical line at the inlet of the diffuser and another one at the outlet of the

diffuser

select Sketch2

click Conceptand select Lines From Sketches

clickApply in Details View

click Generate

click Tools and select Projection

hold ctrl and click on the newly generated edges clickApply in Details View

click the yellow bar at right of Target in Details View, and click on the body

clickApply

click Generate

in Tree Outline, right click on one of the Line Bodyunder 3 Parts, 3 Bodies, and

select Suppress Body

repeat last step for the second Line Body.

Close Design Modelerand go back to Workbench. Save your project.

Mesh

1. Drag Mesh from the left Component Systemslist into the right Project Schematic

workspace

2. drag DM Geometryfrom Geometryto Geometrybelow Mesh

Right click on Mesh and select Edit, the Mesh window will open.


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Boundaries naming

click to reveal the geometry

select inlet wall by using tool

right click and select Create Named Selection

enter Wallinand press OK.

Repeat previous steps to define Walldf, Wallout, Inlet, Outlet, andAxis (it consists of three

segments which you can select holding crtl).

Generate biased structured mesh

Select Meshfrom Outlinewindow

hold ctrland left click on the four vertical segments (Inlet, Outlet, inlet and outlet of

the cone section)

right clickon one of the segments and select Insert / Sizing in Details of Edge Sizing - Sizing window, select Number of Divisions from list Type

and enter 10

select Hardfrom list Behavior

select - - --- -----from list Bias Typeand set the Bias Factorto 5.

Repeat previous steps to insert Sizings to walls and axis segments, the bias in these cases

is not needed. Make 50 divisions to Wallinand to the parallelAxissegment. Set 20divisions

to cone section segments, and 150 divisions to outlet tube segments.

Click in the toolbar

click Mesh in the Outline

ctrl + left click on the three sections of the solution domain

right click and select Insert / Face Meshing

click Generate Mesh from the tool bar.

Click Mesh in the Outline, your mesh should look like this


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Check mesh quality

Click Mesh in the Outline

click Statistics in Details of Mesh window

selectAspect Ratiofrom Mesh Metric list

check whether all the elements have an aspect ratio below 5.

Go back to the Workbenchand save your project.

Running the simulation

Start Fluent component

Drag Fluent component to the work space and link Meshto Setupslot.

Right click on and select Update

right click on and select Refresh

right clickon Setup and select Edit

tickDouble Precisionand click OK.

Setup Fluent

Click Check button, this should not return any error

selectAxysimmetric in 2D Spacefrom Setup / General / Solver mask

Models Select Models / Viscous - Laminar, click Edit button

select k-epsilon (2 eqn) and press OK.

Materials

Select Materials / Fluid / air

click Create/Edit

check whether Density (kg/m3) is 1.225, and Viscosity (kg/m-s) is 1.7894e-05

click Close.

Cell Zone Conditions

Select Cell Zone Conditions / solid-surface_body


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select fluid under Type press OK.

Boundary Conditions

Select Boundary Conditions / inlet, click Edit

insert 10at Velocity Magnitude (m/s)

select Intensity and Hydraulic Diameter fromTurbulence / Specification Method inset 5 toTurbulence Intensity (%), and 0.00623 to Hydaulic Diameter (m)

0.00623 is evaluated from 0.007*d.

select Boundary Conditions / outlet

select outlflow from Type click OK.

Solution Methods

Select Solution / Solution Methods

select Standard from Pressurelist

select Second Order Upwind from Momentum, Turbulent Kinetic Energy, and

Turbulent Dissipation Rate.

Monitors

Click Monitors

select Residual - Print, Plotand click Edit

set allAbsolute Criteriato 1E-06 (be sure to scroll all the way down in the list).

Set variable monitors

Click Surface in the upper tool bar and select Point,,

insert 1 forx coordinate and 0.00000001 for y coordinate

insert aas New Surface Name and click Create

repeat above steps for b (0.26, 0.0445)and c (0.45, 0.07) click Close.

Select Monitorsand click Create at Surface Monitors

enter vel-aas Name

tick Plotbox and select Facet Vaverage from Report Type list

select Velocity from Field Variable list

select a from Surfaces list and click OK.

Create two surface monitors for pressure in b and c. This time, select Pressure from

the list Field Variable.

Solution

ClickSolution Initialization

choose Standard Initialization

select Compute from / inlet

click Initialize.

Click Run Calculation

set 200 to Number of Iterationsand click Calculate.

WHAT WHOULD THESE BE FOR EACH DIFFUSER? USED A(0,0), B(GIVEN), C(GIVEN)


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Post-processingPlease refer to the old version of the CFD notes.

CFD preprocessing ansys Tute

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