14. AIRPLANE GEOMETRY - Rose-Hulman

56 Pages·2006·0.91 MB·English

AIRPLANE GEOMETRY
14. AIRPLANE GEOMETRY
In this tutorial you will import a STEP file that describes the geometry of an airplane
body, including the wing and nacelle that houses the engine. You will clean up the
geometry using GAMBIT smooth/heal and cleanup tools, apply three different types of
size functions, and mesh the geometry using a tetrahedral meshing scheme.
In this tutorial you will learn how to:
• Import a STEP file
• Use a smooth-heal operation to repair the imported geometry
• Use several clean-up operations to clean up the geometry
• Construct a flow volume around the airplane geometry
• Apply size functions to control mesh quality
• Mesh faces using a triangular pave meshing scheme
• Mesh a volume using a tetrahedral meshing scheme
• Prepare the mesh to be read into FLUENT 5/6
14.1 Prerequisites
This tutorial assumes you have worked through Tutorials 1, 6, and 13 and are familiar
with use of the GAMBIT GUI and general clean-up operations.
© Fluent Inc., Mar-06 14-1
Problem Description AIRPLANE GEOMETRY
14.2 Problem Description
Figure 14-1 shows the geometry to be imported and meshed in this tutorial. This geometry
represents one half of an airplane body, including the wing, strut, and nacelle that houses
the engine but does not include the empennage. The imported geometry consists of many
edges and faces that you will eliminate before generating the volume mesh. The mesh
itself will consist entirely of tetrahedral elements.

Figure 14-1: Airplane geometry
14-2 © Fluent Inc., Mar-06
AIRPLANE GEOMETRY Strategy
14.3 Strategy
In this tutorial, you will create a tetrahedral mesh in a flow volume surrounding one half
of an airplane body, including the wing, strut, and nacelle housing the engine but
excluding the empennage. The geometry will be imported as a STEP file containing many
faces and edges that will need to be eliminated before meshing. After creating a flow
volume around the imported geometry and using a GAMBIT smooth/heal operation to
simplify the geometry, you will clean up the geometry using the cleanup tools available in
GAMBIT. You will then create triangular face meshes on the airplane body surfaces and
flow-volume symmetry plane and mesh the flow volume with tetrahedral elements.
NOTE: This tutorial employs a relatively course mesh so that the mesh characteristics can
be easily examined. In actual practice, the model described in this tutorial would employ a
much finer mesh than is used here, especially in the regions adjacent to the airplane body.

© Fluent Inc., Mar-06 14-3
Procedure AIRPLANE GEOMETRY
14.4 Procedure
1. Copy the file
path/Fluent.Inc/gambit2.x/help/tutfiles/airplane.stp
(where 2.x is the GAMBIT version number) from the GAMBIT installation area in
the directory path to your working directory.
2. Start GAMBIT using the session identifier “Airplane”.
Step 1: Select a Solver
1. Choose the solver from the main menu bar:
→
Solver FLUENT 5/6
The choice of a solver dictates the options available in various forms (for
example, the boundary types available in the Specify Boundary Types form). For
some systems, FLUENT 5/6 is the default solver. The solver currently selected is
shown at the top of the GAMBIT GUI.

14-4 © Fluent Inc., Mar-06
AIRPLANE GEOMETRY Procedure
Step 2: Import the STEP File
→ →
File Import STEP …
This command sequence opens the Import STEP File form.

1. Click on the Browse... button.
This action opens the Select File form.
© Fluent Inc., Mar-06 14-5
Procedure AIRPLANE GEOMETRY

a) Select airplane.stp in the Files list.
b) Click Accept on the Select File form.
2. On the Import STEP File form, under Stand-alone Geometry, select the No stand-alone
edges option.
3. Unselect the Make Tolerant option.
The Make tolerant option improves geometric connectivity and can be invoked
either during geometry import or after geometry import—as part of a healing
operation. In this tutorial, you will invoke the Make tolerant option during a
healing operation after examining and addressing duplicate-geometry issues (see
Steps 3 and 4, below).
4. Click Accept.
The STEP file for the airplane body will be read into GAMBIT (see Figure 14-2).
14-6 © Fluent Inc., Mar-06
AIRPLANE GEOMETRY Procedure

Figure 14-2: Imported airplane geometry
© Fluent Inc., Mar-06 14-7
Procedure AIRPLANE GEOMETRY
Step 3: Clean Up Duplicate Faces
The imported geometry is “dirty” in that it contains duplicate faces and edges. In this
step, you will use a GAMBIT cleanup operation to eliminate the duplicate faces.
1. Clean up duplicate faces in the imported geometry.
→ →
TOOLS CLEANUP CLEAN UP DUPLICATE GEOMETRY
R
This command sequence opens the Clean Up Duplicate Faces form.

When you open any of the cleanup forms, such as the Clean Up Duplicate Faces
form, GAMBIT automatically sets the graphics window color mode to display
colors based on connectivity rather than topology. GAMBIT also automatically
sets the graphics window pivot function to the user-specified pivot mode.
a) Retain the Topology-based search option.
b) Click the Default pushbutton located on the right side of the Tolerance text box.
14-8 © Fluent Inc., Mar-06
AIRPLANE GEOMETRY Procedure
When you click the Default pushbutton, GAMBIT displays the Tolerance
default value and populates the Items list with two sets of faces that meet the
tolerance criterion. For the Topology-based search option, the Items list
contains sets of faces that are topologically equivalent to each other and the
edges and surfaces of which are within Tolerance of each other.
c) Select the first duplicate-face set displayed in the Items list.
GAMBIT zooms in on and highlights the faces shown in Figure 14-3. (NOTE:
Due to slight differences in entity numbering between computer platforms, the
entity numbers shown in Figure 14-3 and in all subsequent figures that
include entity labels might differ from those actually displayed in the
GAMBIT graphics window.)

Figure 14-3: Set of faces comprising the first duplicate-face set in the Items list
GAMBIT automatically selects the Method:Connect faces option and populates
the Options:Faces pick list with the faces to be connected in performing the
cleanup operation.
d) Click the A/N pushbutton in the vertical array of pushbuttons located to the right of
the Items list.
© Fluent Inc., Mar-06 14-9
Procedure AIRPLANE GEOMETRY
The A/N (“Apply/Next”) pushbutton applies the Connect faces method to clean
up the duplicate faces and automatically selects the remaining duplicate-face
set in the Items list.
e) Click Apply to clean up the remaining set of duplicate faces.
f) Click the FIT TO WINDOW command button at the top left of the Global
Control toolpad to see the full model geometry in the graphics window.
The removal of the duplicate faces does not significantly affect the appearance
of the airplane geometry.
14-10 © Fluent Inc., Mar-06