CoP simulation comparison, including CFD
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Oh, wow! I did not consider that. CFD is picking up the stall. That is a good explanation!
Hmmm ... so maybe you could write a paper like, say ... "What Barrowman and Galejs left out"
-- kjh
boatgeek
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A look at streamlines at 12 degrees and a little bit on either side should be illuminating. It seems odd that the CP would shift back to the original spot if the fins lost lift due to stall, though.
I think the real takeaway here is that OR sims accurately reflect CP movement, so we likely should go to stability as a percentage of length rather than a strict number of calibers.
rocketguy101
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Would surface pressure plots show the stall on the fins? This is really juicy stuff!
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Working on that...
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Yep, 12 degrees is near the onset of full flow separation off the fins.
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Drag and lift coefficients. Since the model is aligned with the axial and normal directions, I had to do the trig to resolve the forces into the L and D directions.
(Fun fact: Automotive CD is measured along the vehicle axis (direction of travel), not the relative wind.)
The shape of these curves seems reasonable.
(Fun fact: Automotive CD is measured along the vehicle axis (direction of travel), not the relative wind.)
The shape of these curves seems reasonable.
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rocketguy101
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Nice work! Is it possible with the software to get a plot of the surface? When I was in college, I was a CO-OP student at the university wind tunnel. We ran tests for an airplane company that was experiencing stall on their flaps during landing. The techs mixed up diesel and some black powder, painted the model (which was painted white or light gray), and then made a run. Immediately after they took pictures while the flow pattern remained. The results were similar to the picture I attached, except it was not multi-colored I made surface plots of an Alpha running the Solidworks product "Flo Works" many moons ago.
I made surface plots of an Alpha running the Solidworks product "Flo Works" many moons ago.Attachments
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Yes, anything is possible in CFD post-processing. Is there anything in particular you want to see on the rocket surface?
rocketguy101
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I was just curious what the surface pressure plot on the windward and leeward sides looked like. I marked up your diagram from earlier. I've long been curious about Openfoam when a colleague at work recommended it. I'm not a Linux user, and tried to run a bootable Ubuntu session but could not get OF to install properly...I gave up then. My career work has been structural FEA, but I dabbled with CFD at work. Since I retired, I've lost access to the software.
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Here ya go. Leeward and windward sides at 12 degrees angle of attack
If you are a noob and want to play with OpenFOAM, you really want a friendly UI front end. Most are licensed, but a few are freeware. I am using FreeCAD with CfdOF Workbench. There are Windows and Linux installations. Paraview is used for post-processing results.
