|
[Sponsors] |
comparing simulation-experimental values for Cl,Cd |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
May 18, 2001, 18:33 |
comparing simulation-experimental values for Cl,Cd
|
#1 |
Guest
Posts: n/a
|
I am working on a NACA 0012 airfoil.
When comparing the values for the drag and lift coeficient vs. angle of attack with the experimental data from report 824 from NACA ( The 0012 is not available but 0006 and 0009 are similar), my airfoil does'nt stall (loss of lift capacity due to separation of the boundry layer) First I thought it was because the mach number was'nt the same, I changed it so the reynolds number matched, still the same problem. Also, I calculate the Reynolds number and after the simulation, Fluent returns Reynolds that are much smaller. Does anyone know what I`m doing wrong? |
|
May 18, 2001, 19:46 |
Re: comparing simulation-experimental values for C
|
#2 |
Guest
Posts: n/a
|
(1). You have two options: (a). forget about the test data, or (b). forget about the cfd solution. (2). Unless you have a paper which states that they should be the same. I strongly urge you to look for such paper or report first.
|
|
May 21, 2001, 19:36 |
Re: comparing simulation-experimental values for C
|
#3 |
Guest
Posts: n/a
|
Dr Chien,
You say to forget about CFD or about experimental. Why ? I am working hard on numerical simulation of airflow around a Selig 1223 airfoil with Re=171000. The results I got until now are not matching exactly the experiments, but are something ok. I tried modifying the turbulence and near-wall models. And I'll continue trying with another models and using a structured mesh instead. I have the wish to work on CFD codes implementation. Is that a distant truth or can I go trying and will reach some place ? PS: Rodrigo, are you from Brasil ? |
|
May 21, 2001, 21:54 |
Re: comparing simulation-experimental values for C
|
#4 |
Guest
Posts: n/a
|
(1). It is well known that standard k-epsilon two-equation turbulence model is more diffusive. For this reason, the presidcted size of a separation bubble, such as flow over a backward facing step, is always smaller than the test data. (2). So, it is consistent with your solutions which under-predict the flow separation. (3). The way to improve the solution is to improve the turbulence model. This can be done, if you think the test data is the right answer. (4). If you just run the code and ask why they don't match. Then you are creating problems. They are not suppose to match, unless you improve your turbulence model.
|
|
May 21, 2001, 21:56 |
some typing errors
|
#5 |
Guest
Posts: n/a
|
It should be " For this reason,the predicted size of a separation bubble,"
|
|
May 31, 2001, 04:48 |
Re: comparing simulation-experimental values for C
|
#6 |
Guest
Posts: n/a
|
Daniel:
My test data comes from the NACA reports (now its NASA), they have run wind tunnel testing on all their airfoils, but they were made 50 years ago. I found other ones that, with the same Reynolds, have diferent results. I'm a engg. Student from Chile, my University has being working on a airplane built here (Chile), the T-35 Pillan, The results that Fluent has given us are very good, specially the Spallart-Almaras model. This tells us that we are on the right track. |
|
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
TimeVaryingMappedFixedValue | irishdave | OpenFOAM Running, Solving & CFD | 32 | June 16, 2021 06:55 |
max node values exceed max element values in contour plot | jason_t | FLUENT | 0 | August 19, 2009 11:32 |
exact face values | RubenG | Main CFD Forum | 0 | June 22, 2009 11:09 |
Monitor point values in a steady state simulation | Kushagra | CFX | 2 | July 13, 2008 20:03 |
3-D Contaminant Dispersal Simulation | Apple L S Chan | Main CFD Forum | 1 | December 23, 1998 10:06 |