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Lecture 6A:
Geometry Modeling For CFD
Introduction to ANSYS Design
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In this lecture we will learn about:
Fluid Body Extraction
Internal
External
Symmetry Modeling
Watertight Body Preparation & Conformal Meshing
Surface Extensions
Connect
Use of Lines and Sketches for CFD Modeling
Zero Thickness Surface Modeling
Geometry Modeling for CFD
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Preprocessing Workflow
Import/Geometry
Creation
GeometryModifications
Meshing
Sketches and Planes
Geometry Import
Options
3D Operations
Bi-Directional
CAD/ Neutral
Geometry Cleanupand Repair
Automatic
Cleanup
Simplification,
Mid-surface,
Fluid Extraction
Extrude, Revolve,
Sweep, etc
3D Operations
Booleans,Decompose, etc.
Meshing Methods
Hybrid Mesh: Tet,
Prisms, Pyramids
Hexa Dominant,
Sweep meshing
Global Mesh
Settings
Local Mesh Settings
Sizing, Controls,
etc.
Assembly
Meshing
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Fill
Creates internal fluid volume
Two options By Cavity : user must select all wetted surfaces
By Caps : user must create closing surfaces at
inlets and outlets, and select bodies
Details View of Fill
Internal fluid volumeextracted using Fill
Cap surface bodies
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Enclosure
Creates enclosure around the bodies
Useful for external aerodynamic analysis
Can be used for extracting internal flow domain
Input
All or selected bodies
Shape of enclosure
Extent of enclosure
Output
A frozen body around the selected parts with specified extents
Internal flow volume as a result of automatic Boolean subtract
Supports symmetry models
Full or partial models can be included in enclosureEnclosure cre
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Enclosure: External Flow Example
Model
Using Symmetry
User Defined Shape
Enclosure
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Symmetry
Defines symmetry for the model
Input
All or selected bodies
Up to three symmetry planes
Operation
Symmetry planes slice the model
Output
Sliced model (part lying on the positive side of the axis is retained)
Details View of
Note: Faces that a
the symmetry pla
Symmetry namUsing Symmetry
Tip:
as vis
disco
(aftesupp
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Surface Extension
Allows extension of surface bodies to the desired extent
Extension type
Natural: Based on gradients of selected edges
User Defined: User specifies the direction
Model with gap Model with ga
Details View of Surface
Extension
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Connect
Aligns and possibly joins a set of
Vertices
edges
faces
Properties
Location property
T-junction property
Details
Vertex Connect
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Connect: Edge Connect Example
Model with a gap
Location:
Interpolated
Location:
Preserve First
Both edges moved to interp
Second edge moved to first
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Connect: Edge Connect Example T-junc
Model with a gap
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Connect After Shared Topology
Connect featurecan be used afterthe Shared Topology feature
to selectively share faces between two bodies of a multibody
part. This can be used to:
Fix face sharing failures after Shared Topology
Can be used for selective sharing of faces in conjunction with
Selective Shared Topology
The advantageof Connect feature is that
It takes user defined tolerances to Connect faces which
failed due to smaller Shared Topology tolerance
This ensures conformal meshing
Please be careful in choosing tolerance value, as high
values may result in deformation of model at some places
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Concept Modeling Tools
Why is Concept Modeling(Lines and Faces) relevant for CFD users?
Sometimes the imported files contain issues like: Missing Faces
Corrupt Faces
Details which require cleanup by selective geometry recreation
For cleaning, patching, recreating surfaces & stitching a water tight body, s
surface creation options of concept modeling are used
CFD models also require some solids/thin bodies to be modeled as ze
surfaces
Examples are baffles, fins, zero thickness pipe walls, fan shrouds, etc.
For above mentioned cases mid-surfacing tools need to be used
Sometimes 2D modeling operations also require use of concept mod
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Lines from Points
[Main Menu] Concept Lines From Points
Points can be any
2D sketch point
3D model vertex
Point Feature (PF)
A point segment is a straight line connecting
two selected points.
The feature can produce multiple Line Bodies,depending on the connectivity of the chosen
point segments.
Point 1
Line Body
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Lines from Edges
[Main Menu] Concept Lines From Edge
Creates line bodies based on existing 2D and 3D model edges
Can produce multiple line bodies depending on the connectivity
of the selected edges and faces
Can select edges and/or faces through two fields in the detail
window then Apply
Line Bodies
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Split Edges
[Main Menu] Concept Split Edges
Splits edges (including line body edges) into two or more pieces Fractional: Value of 0.5 splits the edge into two edges of equal length
Split by Delta: Distance between each split is given by Delta along the
edge.
Split by N: Number of Divisions of the Edge
By Split Location: By Fraction or By Coordinates
Selected line Fraction = 0.5 Fraction = 0.25
Fractional:
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Surfaces From Edges
[Main Menu] Concept Surfaces from Edges
Creates surface body using existing body edges,including line body edges as the boundary
Can be solid or line body edges
Edges must form non-intersecting closed loops
Each closed loop creates a frozen Surface Body
The loops should form a shape such that a simplesurface can be inserted into the model as
planes, cylinders, tori, cones, spheres and
simple twisted surfaces
Twisted surface
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Surfaces From Sketches
[Main Menu] Concept Surfaces from Sketches
Creates surface bodies using sketches as boundaries(single or multiple sketches are OK)
Base sketches must be closed profiles which are not
self-intersecting
May choose to Add or Add Frozen operations
Can reverse normal direction No in Orient WithPlane Normal field
Can enter thickness which will be used in creating
the FE model
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Mid-Surface
Extracts surface body that is midway between existing
solid body faces
Two Options:
Manual: Operates only on user specified face pairs
Automatic: Provides option to search for other
matching face pairs
Details View of Mid-SurfaceMid-Su
p
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Summary
What have we learnt in this session?
Fluid Body Extraction
Symmetry Modeling
Watertight Body Preparation & Duplicate Face Removal
Modeling of Lines and Surfaces for Simplification/Repair
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Workshop 6.1AGeometry Cleanup &Extraction
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Micro-Workshop: 2
Objective:
Create an Enclosure for extracting external fluid region