|
[Sponsors] |
Drag and lift coefficients of a oscillating cylinder |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
March 7, 2017, 13:47 |
Drag and lift coefficients of a oscillating cylinder
|
#1 |
New Member
Join Date: Mar 2017
Posts: 4
Rep Power: 9 |
Hello my friends,
I am simulating the flow around a oscillating cylinder (forced oscillation). For that, I used a UDF I found here at cfd-online. No problem regarding that, I can even see the oscillation in the solution's final animation. However, I am facing a problem with the drag and lift monitors. Both return oscillating values (as expected), but those are in the figures of 10E4 or more, and show no major frequency of oscillation. In the literature, these Cd and CL values hardly go greater than 2.5 (when lock-in occurs, which my case is far from). So far, I tried changing from the k-epsilon to the SST model; checked the mesh scale and the reference values; tested out different parameters of remeshing and smoothing (dynamic mesh); and even took the forces from Fluent and made some calculations by my own (which gave me results near those ridiculous values ). Now, I have no clue of what's causing this error, so here am I recurring to you guys - do you have any idea of what may be happening? For your information, I am considering a 0.2m cylinder diameter with a inlet-velocity of 9E-4m/s, which gives a Reynolds=200. The oscillation has a 0.03m amplitude and frequency=0.16Hz. The fluid is water and the timestep is 0.02sec. I wonder if this velocity is "too small" for Fluent maybe? Hope you guys can save me in this one hahah |
|
March 8, 2017, 04:46 |
|
#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,762
Rep Power: 66 |
You are grasping at straws here. If that was the case you should blame your computer for not having quadruple precision .
A 200 mm diameter oscillating +/- 30 mm in water... That's not really an oscillating cylinder but a torpedo or small boat maybe? I would expect "large" forces. Are you sure you didn't use density of air or something instead of water to calculate the coefficients? |
|
March 8, 2017, 18:04 |
|
#3 |
New Member
Join Date: Mar 2017
Posts: 4
Rep Power: 9 |
Thanks for the help, LuckyTran.
What do you mean exactly by "quadruple precision"? Because in the Fluent Launcher I only see a "Double Precision" in the options, which I marked. Would there be a third or fourth precision? [Probably I am grasping at straws in fact, but I tried many options and none of them seemed to help anything. I am getting tired of trying hahah]. Also, do you think it is in fact expected high force values? Maybe if I changed the oscillation's parameters I would get lower numbers, what do you think? Once again, thank you for helping, at least I can discuss this matter with someone |
|
March 8, 2017, 18:27 |
|
#4 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,762
Rep Power: 66 |
There is no third or fourth precision. That is exactly my point. The reason there is no third or fourth precision is not Fluent's fault, but simply that your machine does not have it. If you want to blame really small numbers, then you need to call IEEE and have them come up with a triple/quadruple standard.
Do you even get the correct drag coefficient for a stationary cylinder? |
|
March 8, 2017, 20:45 |
|
#5 |
New Member
Join Date: Mar 2017
Posts: 4
Rep Power: 9 |
Ok, I got it. I'll try a smaller diameter, bigger velocity combination, keeping Re=200. Maybe it will work finally.
Yes, it worked just fine for a stationary cylinder. Thank you sir, I'll let you know any news. |
|
Tags |
drag coefficient, fluent 16.0, lift coefficient, oscillating cylinder |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Lift and Drag coefficients for flow past sphere | shashanktiwari619 | FLUENT | 0 | January 27, 2017 14:31 |
wrong SU2 calculation for lift and drag coefficient for NAC4421 | mechy | SU2 | 7 | January 9, 2017 06:18 |
How to compute lift and drag coefficients for flow past a fixed cylinder? | antonella.longo@ingv.it | Main CFD Forum | 2 | May 11, 2016 18:26 |
lift and drag coefficients around a ground vehicle | Pedro | CFX | 3 | September 5, 2012 19:31 |
Lift and Drag Coefficients Reliability | Luis | FLUENT | 2 | December 27, 2005 15:45 |