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## Simulation CFD

Contributor
Posts: 14
Registered: ‎01-18-2012

# Inviscid Analysis

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01-18-2012 06:47 AM

Does anybody have an idea of how one might approach an inviscid (essentially potential flow) analysis using CFDesign/Simulation CFD?  Is this even possible?  Any advice would be appreciated.  Thanks.

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Product Support
Posts: 645
Registered: ‎08-24-2011

# Re: Inviscid Analysis

01-18-2012 07:02 AM in reply to: matthew.brown

Hi Matt,

This is possible!

Procedure for simulating an Euler (inviscid) flow solution with standard solvers:

1. Create a material with a viscosity of 0 (or very close to 0).

2. Assign slip to all the solid walls

This removes viscosity from the solution.

Another option is that you could use the 'Quick Forced' solver (Quick Forced has a potential flow solver).  Solving for potential flow naturally ignores wall constraints and fluid visocity so the above settings do not need to be followed.

Note: a viscosity that is exactly 0 can cause solution instability. If you see this, use a value that is very close to 0 (such as 0.000001 Poise).

(LINK)

Royce Abel
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Contributor
Posts: 14
Registered: ‎01-18-2012

# Re: Inviscid Analysis

01-18-2012 07:09 AM in reply to: Royce_adsk

Royce,

Thanks! I will give this a shot.   I am curious though, why the slip BC at the walls?

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Product Support
Posts: 645
Registered: ‎08-24-2011

# Re: Inviscid Analysis

01-18-2012 07:35 AM in reply to: matthew.brown

When you make the assumption of Inviscid flow you also expect that there be slip at the walls, therefore you need to add the slips.  Otherwise you would still get a 0 velocity along the walls.

-Royce

Royce Abel
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Contributor
Posts: 14
Registered: ‎01-18-2012

# Re: Inviscid Analysis

01-18-2012 02:08 PM in reply to: matthew.brown

This (sort of) worked.  I was not able to get it to run smoothly using viscosities less than 1e-4 poise, and even then I needed the 'Check Velocity Distribution' flag file command to get it to finish.  Ultimately, however, this did not get me to the results I was shooting for.  There is still a large amount of laminar separation, which is what I was trying to avoid, so that I could check the results of a potential flow calculation.  Any thoughts?

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Product Support
Posts: 645
Registered: ‎08-24-2011

# Re: Inviscid Analysis

01-18-2012 02:15 PM in reply to: matthew.brown

Would is be possible for you to share your support share file?  Would you consider it NDA or have something that you could mock up quickly?  Otherwise we will have to take it offline to a real case.

-Royce

Royce Abel
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Contributor
Posts: 14
Registered: ‎01-18-2012

# Re: Inviscid Analysis

01-18-2012 02:37 PM in reply to: matthew.brown

Royce,

It is not proprietary.  The file is supposed to represent an annular NACA 66(2)-015 airfoil.  There are experimental and potential analysis results published in Lewis, 'Vortex Element Methods for Fluid Dynamic Analysis of Engineering Systems' Cambridge University Press, (C) 1991.  He offers a Pascal code in the back which we are trying to use, but his code results do not match what he published.  We are trying to decide if his results are incorrect or if it is his code that is faulty.  The analysis is laminar and axisymmetric in X.  Also, I am using CFDesign 2010 not Simulation CFD if that makes a difference.

That all being said, the website will not let me attach a *.cfz file.  I get the following error:

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Product Support
Posts: 645
Registered: ‎08-24-2011

# Re: Inviscid Analysis

01-18-2012 02:39 PM in reply to: matthew.brown

That is odd.

Change the extension to .cfz.txt

-Royce

Royce Abel
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Contributor
Posts: 14
Registered: ‎01-18-2012

# Re: Inviscid Analysis

01-18-2012 02:41 PM in reply to: matthew.brown

Here ya go!

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Product Support
Posts: 645
Registered: ‎08-24-2011

# Re: Inviscid Analysis

01-18-2012 02:59 PM in reply to: matthew.brown

Matt,

Do you have access to CFD 2012?

-Royce

Royce Abel
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