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June 8, 2009, 04:55 |
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#21 | ||||
Senior Member
andy
Join Date: May 2009
Posts: 301
Rep Power: 18 |
Quote:
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I am curious about why you and a significant numbers of other posters here seem to be in this position. In the early stages of learning about CFD, I would suggest that lots of quick 2D simulations with a range of parametric changes is going to teach you a great deal more than a few, probably failed, 3D simulations. The reason for asking is because this puts you in a Reynolds number range where the physics of the flow does not change substantially enabling simpler approaches to turbulence modelling to be reliable. Quote:
How much time on a reasonable sized parallel computer do you have to support a set of adequately resolved LES simulations? If you do not have this resource, and it would be odd if you did given that you are clearly not resourced in other ways, I would suggest dropping two of the dimensions and using 2D steady state at least initially. |
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June 8, 2009, 05:47 |
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#22 |
Senior Member
Prapanch Nair
Join Date: Mar 2009
Location: Bangalore, India
Posts: 105
Rep Power: 17 |
Thank you for the clarifications Andy.
Unfortunately the forums are confusing sometimes and once one gets to a forum, he is bombarded with ideas, mostly trivial. In fact I didn't think there would be a vortex street at this reynold's number, otherwise why would the properties (like Cd) reach a plateau after 10^7. The idea that there will be a good vortex shedding at Re 10^7 was from another member. I couldn't find the truth behind it, because I couldn't read it in any of the books available with me. A few papers i could find were in the Re of 10^5 - 10^6. And almost all papers/books said that properties like Cd would reach a plateau after 10^7. But I couldn't find relavant work published related to this. The package I use is opensource. The only way I could understand it is by reading the code and talking to people(not good documentation available). It takes iterations to get me somewhere, I am aware of it and would take it really serious when I try to publish some work. And the inletOutlet condition behaves in the way I mentioned before. I was not sure what physical situation I could aptly apply it. A lot of people are indeed in my position. And I believe this is owing to the vastness of CFD. I had worked on high speed flows, written Euler equation solvers. But when it comes to incompressible slow flows, I am baffled. I hope, with inputs from learned people like you, I would be able to do quality simulations in the future. You had been really helpful, I really appreciate your advices. I would act accordingly and post my results here. Thank you Prapanj. |
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September 14, 2009, 23:20 |
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#23 |
Senior Member
Steve Hansel
Join Date: Jun 2009
Location: Colorado, USA
Posts: 112
Rep Power: 17 |
If you run your cylinder right up to the symmetryPlane aren't you essentially simulating an infinite cylinder, not one 28 m tall? Also is a 1m grid size fine enough for this problem?
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September 15, 2009, 01:29 |
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#24 |
Senior Member
Prapanch Nair
Join Date: Mar 2009
Location: Bangalore, India
Posts: 105
Rep Power: 17 |
Hi Hansel,
The problem is that of an infinite cylinder essential. I had a span of 28 m because I wanted to have sufficient 3 dimensionality in the domain. Because at a later stage I would be simulation a few other cylinders in the same domain that work as a stack, and study the interference effect. The grid size is not 1m, the y plus is between 0.4 and 50, with an average of around 10. Thanks, Prapanj |
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Tags |
coefficient of drag, high re, k omega, turbulence |
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