[AndrewLittle]

Hello Everyone,

I am quite new to the forum and would like to introduce myself. I am a Mechanical Engineer working in Michigan. I have a BS degree in Mechanical Engineering from Kettering University and have always had great interest in fluid flow and aerodynamics. I have a small amount of CFD experience and I finally have the opportunity to design something where aerodynamics, lift, drag, and control are keys areas of concern.

My first question is about Stallion 3D. I have searched the forums a little bit and have yet to find much information about. Does anyone have any experience using this program?

Thanks and I look forward to your responses,
Andrew Little,

[AndrewLittle]

Well it appears some of my fears have been confirmed with this product. It appears to be not very widely used in the CFD community.

Does anyone have a suggestion on a software to use? I plan on looking into the Open Foam code in the near future, however the holidays and my new born son are taking up a lot of my time (not a bad thing if you ask me!).

Overall, I am trying to determine the L/D of an airframe at various speeds and angles of attack.

Thanks again for your help.
Andy,

[cdegroot]

Hi there. I think you are right. I have never heard of Stallion 3D before and I've been in CFD for quite a few years. Personally, I use a code that I developed as well as ANSYS CFX (and occasionally ANSYS Fluent) for my work. I think OpenFOAM is a good option, especially if you don't have a large software budget. Lots of people use it so you should be able to find lots of help. I don't use it myself, but I understand the learning curve is probably greater than a commercial code like ANSYS. Maybe an OpenFOAM user can comment on this.

[mgd]

OpenFOAM is a good option, but as cdegroot already mentioned, the learning curve is steep - especially if you don't already have a PhD in fluid dynamics and numerical methods!
There are some good examples with OpenFOAM, and a lot of good information on the forums and internet which certainly helps. Another possibility is the Stanford SU2 code. I've only just started working through the tutorials, but so far am quite impressed and the more focussed nature of the code for external aero (rather than the general purpose mathematical toolbox approach of OpenFOAM) might make it quicker to pick up and use for your application. There isn't an active forum that I've managed to find yet, but I get the impression that that may be changing soon.
Regardless of what you use, just remember - it is quite easy to get results out of whichever code you choose, just not necessarily the right results...

[agd]

For external aero calculations, you might also look at ISAAC. It is available from sourceforge. It is a structured-grid, density-based solver written in FORTRAN, and incorporates a decent set of widely used algorithms for flux calculations and turbulence modeling. I have not modeled anything with it, however, so this recommendation should be taken with a grain of salt. My experience with it thus far is restricted to assisting some students in setting it up, and also in reviewing some of the source code. I can say that under Ubuntu linux it was very easy to build, and it comes with several example cases involving airfoils.

[shirazbj]

Originally Posted by AndrewLittle

Well it appears some of my fears have been confirmed with this product. It appears to be not very widely used in the CFD community.

Andy,

I googled a little. It seems this Stallion 3D is quite good. At least it is easy to use. Can use CAD model.

[AndrewLittle]

Thanks for the information everyone. I will have to look into each of the codes you've discussed. Now if only I didn't have hobby "A.D.D." i might actually get one of them up and running on my personal computer as well.

Unfortunately, I haven't received much help from Hanley Innovations (creator of Stallion 3d) as of late. I sent them an e-mail a few weeks ago and haven't received a reply yet. Hopefully the voice mail I left them will yield some results.

Andy,

[PatrickHanley]

I am Dr. Hanley, the owner of Hanley Innovations. I noticed this post by Andrew Little. Just wanted to add that Andrew purchased Stallion 3D and corresponded with me well before he started this thread. I wanted to add his email thread to this post so that all the information is available to the CFD community. Andrew purchased the program on November 1st, 2012. Please note the dates of the emails.

Thanks for reading.

------- This is the log of my correspondence with Andrew (latest first)-------

Dear Patrick,

Thank you for the information. It was very helpful. I've rerun my analysis and it dropped our drag significantly. We're still not where we would like to be, but we're getting there. I have a few more questions if you're willing to entertain a young aerodynamicist!

1. Fluid volume - I've been keeping the volume at the standard 20 meter cube. Will reducing the size of that cube reduce my analysis time? My wing span is only 12 feet so I'm assuming a 20 ft cube might suffice.

2. Weight & C/G Location - I noticed in your videos and tutorials you don't place the C/G of your planes where I would expect them to be. Generally you leave it at the 0,0,0 coordinate. Also you didn't mention modifying the system weight either. Is there a specific reason for this?

3. Cells Near Boundary - Would further increasing the number of cells at the boundary layer increase the accuracy of my results. We are looking to save 10-20 watts of power at a time, so minor changes can be a big influence on our overall flight time.

4. Initial Cell Division - If I increase my cell division from 6 to 10 in the x and z direction will I further increase the accuracy of my results.

Thanks again for all of your help.

Andy,


Andrew Little

Mechanical Engineer/Designer

Merrill Tool & Machine

-Defense Systems

alittle@merrilltg.com

www.merrilltg.com

586-354-2323 ext. 4105

>>> "Hanley Innovations" <hanley@hanleyinnovations.com> 11/12/2012 12:30 AM >>>

Dear Andrew,

Thanks for your email.

Because your aspect ratio is high, you will probably have to select more cells in the solution (above 480,000). In addition, you must choose 3 cells near the boundary to compute better drag number. Also, please choose more initial point in the x and z direction for the initial grid. I would suggest that you use 6 in the x and z direction and 2 in the y-direction for the initial grid.

Another option is to solve half of the wing by using the mirror image option.

Please let me know if have any questions.


Best regards,
Patrick


Patrick Hanley, Ph.D.
Owner
http://www.hanleyinnovations.com
Tel: (352) 240-3658
eMail: hanley@hanleyinnovations.com
----- Original Message -----
From: Andrew Little
To: Hanley Innovations
Sent: Friday, November 09, 2012 3:10 PM
Subject: Lift-To-Drag Ratios


Dear Patrick,

I am running into a small issue, or potential issue, with my drag numbers. My plane is very similar to a competition R/C sailplane, yet I'm get L/D ratios of 5:1 or 4:1. I was expecting something in the mid 20:1 range.

I may be inputing something in correctly. Is there anything in particular I need to watch out for when analyzing a plane with a high aspect ratio?

I'm looking at about a 12 foot wingspan and an average chord of 8".

I also noticed that in your tutorials you don't change the weight or C/G location at all. Is there a specific reason for this?

Thanks again,
Andy





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