How to Use Sim CFD (to Your

Advantage)

- A Primer for Computational

Fluid Dynamics

Jim Swain Dave Graves

Synergis Autodesk

How to Use CFD

• When to apply simulation tools in a product development project.

• See a basic CFD workflow for consumer electronics cooling.

• Discuss basic CFD considerations for building design.

• See tools to prepare Inventor models for simulation.

We will be using Autodesk CFD 2016 and related products.

Applications Consultant for

Synergis

Simulation user:

Designer

Generalist

Jim Swain

Channel Enablement Executive

for Autodesk

Simulation user:

Designer

Simulation Generalist

CFD Specialist

Dave Graves

When is simulation traditionally performed?

Completed design performance verification

Failure analysis

When to Apply Simulation Tools?

When can it save the most money???

Early in the concept phase!!!

Why?

Parts haven’t been spec’d, or ordered

Rough designs = less simplification time

Comparing concepts for relative improvements

Avoids “does it match our test lab results?”

When Should We Apply Simulation Tools?

CFD Workflow – The 3048 Meter View

Open the (simplified) model in Inventor.

Simulation tab

Autodesk CFD 2016 > Active Model Assessment Tool

Inventor to CFD

Active Model Assessment Tool

Setup the Analysis

Prepare the model geometry

Apply materials

Apply boundary conditions

Apply initial conditions

Apply mesh settings

Apply analysis settings

Run the Analysis

Explore the Results

Overall Workflow

Prepare the model geometry

Apply materials

Apply boundary conditions

Apply initial conditions

Apply mesh settings

Apply analysis settings

Setup

Prepare the model geometry

Setup

Setup

Apply materials

Setup

Apply boundary conditions

Setup

Apply initial conditions

Setup

Apply meshing

Solve

Change to the Results tab

Probably will have to hide the

outer shell.

Don’t hide the working fluid!!!

Can start checking results right

after the first iteration is complete.

Analysis Results

Mechanical Ventilation

HVAC: Factories, Datacenters,

Hospital Rooms, Office Spaces,

Laboratories, Clean Rooms

Smoke Extraction

Chemical Spill Control

Thermal Comfort

Solar Loading

Condensation on Windows

Typical AEC Models Studied with Simulation CFD

External Flow

Wind Loading

Smoke/Exhaust

Flow control on

environment: Fences, walls,

courtyards

Natural Ventilation

Passive building comfort

studies

Large Atriums

Condensation

Internal/External

combinations

Sometimes it is better to start over!

Architectural drawings are overly complex for CFD Simulations

Start cleaning the geometry with the basic building geometry:

1. Open VG (Visual Graphics)

2. Turn off all layers

3. Turn on Walls, Floors, Roofs, Ceilings, Windows

4. Start your clean up there

5. Modify Geometry – Test Launch – Inspect Model – Test Mesh

Repeat 5 until geometry is satisfactory

Elements hidden from the active 3D view in Revit are not transferred into

Autodesk Simulation CFD.

Leveraging your Revit model in Simulation CFD

Model Complexity

Well-formed geometry with an appropriate level of detail is essential for an efficient AEC

simulation.

Architectural geometric models often include features that span a wide range of length scales.

Consider the effect and relevance of small geometric features on the overall simulation.

A detail item that is 1/8” long embedded in a 10,000 square foot interior space will require

mesh elements that are significantly smaller than the surrounding air volume. If the item is

included, the resulting model size is much larger due to the large element count, and run-

times are much longer as well.

• Remove or simplify small features on furniture or detailing.

• Either exclude or substitute features such as small diameter tubing, rounds, fillets, holes, handles, and

railings with a simpler representation.

Remove as necessary to

maintain simulation efficiency.

© 2014 Autodesk Autodesk Technical Academy 2014

Model Complexity

© 2014 Autodesk Autodesk Technical Academy 2014

Revit GeometryWhen Using Windows: Leverage Level of Detail (Coarse vs Fine)

© 2014 Autodesk Autodesk Technical Academy 2014

Outcome:

Diffusers

Sidewall Slot DiffusersCeiling Supply

Most diffusers are built from scratch

Build the model with volumes, don’t use surfaces!

Customer have to build their own libraries in Revit

© 2014 Autodesk Autodesk Technical Academy 2014

Furniture

Model Integrity

Inspect closely for interferences and small gaps.

The following techniques references Revit commands, but the strategy can be applied to any

CAD tool.

Ensure walls, floors, and ceilings meet cleanly. Avoid small overlaps or gaps.

• This prevents a high concentration of very small elements where these features meet.

• Causes meshing failure and poor results.

• To review details of the construction, use the Thin Lines view option.

• To ensure walls are cleanly lined up, use the Join and Align commands.

• Small interferences and gaps between structural elements (such columns and beams) and neighboring

geometry should also be considered

In the image, small interferences exist between structure and cladding around the outside of the

column and beams:

© 2014 Autodesk Autodesk Technical Academy 2014

General Geometry ConcernsFinding Leaks

1. Create a volume around the entire model with the

External Volume Geometry tool in Autodesk Simulation

CFD.

2. Assign a solid material to all parts in the model. Assign

Air to the surrounding volume.

3. On the Solve dialog, click Results quantities, and enable

Stream Function. (This enables nodal aspect ratio as an

output quantity.)

4. To generate the mesh, set the number of iterations to 0

on the Control tab of the Solve dialog,, and click Solve.

5. After the mesh is complete, create an Iso Surface, and

show Nodal Aspect Ratio. The regions with the highest

Nodal Aspect Ratio are often the gaps.

Note: If this doesn’t mesh then you have major geometry

issues.

Simplify tools in Inventor

Shrinkwrap

Simply

Delete Face (Direct Edit)

SimStudio

General Simplifying Tools

Automatic Model Diagnostics and RepairEasily find and fix geometry integrity issues before they affect your mesh

Rapid Model Defeaturing and SimplificationRun simulations faster by eliminating unnecessary detail

Intuitive Simulation Feature CreationCreate sim-specific features like 2D shells, caps, etc.

© 2015 Autodesk, Inc. ATA 2015: Evolve to Drive Adoption

Wrap almost any solid or surface geometry

Creates a CFD volume mesh

CFD 2016 – Geometry and MeshingAutomated Surface Wrapper

Early!!!

Initial concept development

Why: Verify design feasibility.

Who: Project Engineer, Analyst

Conceptual models

Component development

Why: Early design verification.

Who: Project Engineer, Analyst

Production models

Recap - When to Apply Simulation Tools?

Questions?

Thank you!

Conclusion