dm-intro 15.0 l06a geometry modeling for cfd

1 © 2013 ANSYS, Inc. February 7, 2014 ANSYS Confidential

15.0 Release

Lecture 6A:

Geometry Modeling For CFD

Introduction to ANSYS DesignModeler


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


Preprocessing Workflow

Sketches and Planes

Geometry Import Options

3D Operations

Bi-Directional

CAD/ Neutral

Geometry Cleanup and Repair

Automatic

Cleanup

Simplification,

Mid-surface,

Fluid Extraction

Extrude, Revolve,

Sweep, etc

3D Operations

Booleans,

Decompose, etc.

Import/ Geometry Creation

Geometry Modifications

Meshing Solver

Meshing Methods

Hybrid Mesh: Tet,

Prisms, Pyramids

Hexa Dominant,

Sweep meshing

Global Mesh Settings

Local Mesh Settings

Sizing, Controls,

etc.

Assembly

Meshing


• 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

Fill

Details View of Fill

Internal fluid volume extracted using Fill

Cap surface bodies must be selected

movies/fill_by_cavity.swf


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 enclosure

Enclosure created for an airplane


Enclosure: External Flow Example

Model

Using Symmetry

User Defined Shape Enclosure


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 Symmetry

Note : Faces that are coincident with the symmetry plane are tagged with a “Symmetry” named selection under AMP

Using Symmetry

Tip: The symmetry tool can be used as visualization tool when discovering the model (then the operation is deleted)


Symmetry: Example

Full Model

Symmetry using XY plane

Symmetry using XY & ZX plane


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 gap closed

Details View of Surface Extension

movies/surface_extension_natural.swf


Connect

• Aligns and possibly joins a set of vertices, edges or faces

• Properties

– Location property

– T-junction property

Details View of Connect

Vertex Connect


Connect: Example (1)

Edge Connect

Model with a gap

Location: Interpolated

Location: Preserve First

Both edges moved to interpolated location

Second edge moved to first edge location



Edge Connect

Model with a gap Using

T-Junction


Face Connect

• Additional options as per edge connect


Model with a gap


Connect After Shared Topology

• Connect feature can be used after the Share Topology feature to selectively share faces between two bodies of a multibody part

– This can be used to:

• Fix face sharing failures after Shared Toplogy

• Can be used for Selective sharing of faces in conjunction with Selective Shared Topology

• The advantage of Connect feature is that

– It takes user defined tolerance 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


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, several line and surface creation options of concept modeling are used

• CFD models also require some solids/thin bodies to be modeled as zero thickness 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 modeling tools

Concept Modeling Tools


Lines from Points

[Main Menu] Concept Lines From Points

– Points can be any 2D sketch points, 3D model vertices or Point Feature (PF) points.

– 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

Point 2

Line Body


Lines from Edges

[Main Menu] Concept Lines From Edges

– 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


Selected line Fraction = 0.5 Fraction = 0.25

Split Edges

[Main Menu] Concept Split Edges – Splits line body edges into two pieces

– Split location is controlled by the Fraction property (e.g. 0.5 = split in half).

– Other Options:

• Split by Delta: Distance between each split is given by Delta along the edge

• Split by N: Number of Divisions of the Edge


Surfaces From Edges (1)

[Main Menu] Concept Surfaces from Edges

– Creates surface body using line body edges as the boundary

– Line body edges must form non-intersecting closed loops

– Each closed loop creates a frozen Surface Body

– The loops should form a shape such that a simple surface can be inserted into the model:

• Planes, cylinders, tori, cones, spheres and simple twisted surfaces

Planar surface Non-planar surface


Surfaces From Edges (2)

• Creates surfaces from existing body edges

• Can be solid or line body edges

• Edges must produce non-intersecting closed loops

Existing solid body edges are selected for new surface boundary.

New, frozen, surface body generated (note, solid body is hidden).


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 With Plane Normal field – Can enter thickness which will be used in creating the FE model


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-Surface

Mid-Surface created for a pipe geometry


Mid-Surface: Manual

Manual Method • Set the Selection Method to “Manual”

• Select pair of faces, one pair at a time, in Face Pairs input

• The order of selection determines the surface normal direction

• Notice the first surface picked is displayed in purple, the second is shown in pink

• When the selection is finalized the selected pairs are displayed in dark and light blue colors

Details View of Mid-Surface

2nd Pick

1st Pick

Normal Direction

Solid Model Color of faces during selection Color of faces after selection


Mid-Surface: Automatic

Automatic Method • Switching the Selection Method from “Manual” to “Automatic” exposes several additional

options

– Bodies to search: Limits search to visible bodies, selected bodies or all bodies

– Minimum and maximum threshold sets search range (thickness) for face pairs

• Options like Extra Trimming are very useful with “Automatic” method

– Provides options for situations where trimming problems with surface bodies occur

• Preserve Bodies? allows you to save the solid bodies from which surfaces are created (default is No)


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


Workshop 6.1A – Geometry Cleanup & Fluid Extraction


Objective:

• Create an Enclosure for extracting external fluid region

Micro-Workshop: 2

dm-intro 15.0 l06a geometry modeling for cfd

Documents

ansys confidential symmetry

ansys confidential enclosure

model symmetry

ansys designmodeler

symmetry models

symmetry tool

symmetry tip

symmetry note