CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   cfd simulation of an uav (http://www.cfd-online.com/Forums/cfx/85695-cfd-simulation-uav.html)

prshet March 4, 2011 12:40

cfd simulation of an uav
 
i've been working on an uav model with a span of around 2m and fuselage lenght around 1m. the inlet velocity(as per the experimental results) is 21m/s.
the results for Cl are matching closely for lower angle of attack, but the problem is i'm not able to get the right stalling angle. i've generated an unstructured mesh(with prism layers) with around 1.2 million elements using ICEM. i've used k-omega turbulence model, also i've done an itterative convergence study for one case. also as a further part of my work i would like to carryout fluttering analysis for the wing, which needs moving mesh. as i'm new to this please suggest what work should i carry out further....?

ghorrocks March 6, 2011 18:12

Capturing the stall point is tricky. Have a look in the literature to find out how other simulation researchers do it. It is not my field so I do not know.

prshet March 7, 2011 01:08

ya i'm already working on it. i'm try now for a structured mesh, this will help me have a better control over the problem. but for analyzing a flutter problem for the airfoil i'll have to generate moving mesh. can you please suggest me on this, it would be really helpful.

Attesz March 7, 2011 08:10

Getting closer to the stall point the steady state results won't match with experimentals, because of transient effects (growing vortex shedding etc). Switching to transient solver can handle this problem. I would use adaptive time step to speed up the simulation.
In flutter I have no experience also, but this is good challenge in cfd :)

prshet March 8, 2011 08:56

i havent tried with the transient solver, but will it be effective even for lower velocities (around 22m/s). and more over i've used an unstructured mesh(tetra) will it be advisable to go for structured mesh for higher angle of attack.....? :)

Attesz March 8, 2011 11:15

Quote:

will it be advisable to go for structured mesh for higher angle of attack
i don't think so...
post pictures of your mesh!

prshet March 8, 2011 14:10

pictures of my mesh
 
ya certainly, i'll mail them to u. thanks a lot for ur suggestions. :)

prshet March 10, 2011 10:28

sir could i please get your email id....... so that i can mail u the contours and other details.

Attesz March 11, 2011 07:02

if you are able to do, post pictures here because other people can see it.

prshet March 11, 2011 08:30

i would have certainly posted them here, but i cannot upload attachments in the threads. i feel its not permitted to upload attachments. so it would be helpful if u could give me your email id. looking forward for your reply.:)

Attesz March 11, 2011 09:03

felfoldi.attila@gmail.com but try upload here if you can. maybe you should delete the cookies if you have problems with the site.

prshet March 15, 2011 11:01

further improvements
 
i have been successful in getting the stall angle and the Cl is matching quite well with the experimental results. what further improvements can be done on the problem....? i've been thinking of drag reduction using winglets but i dont have the data for the specific winglet. what further improvements can be done.....?

icemaniac178 May 18, 2011 03:17

mr prshet,
can you share with me how have you been successfully getting the stall angle? i believe i had the same problem with u.

prshet May 20, 2011 02:32

ya certainly..... can u tell me the mesh details.....? and wht r ur inlet conditions......? if u pls let me know i would be able to help u....

icemaniac178 May 21, 2011 01:17

Quote:

Originally Posted by prshet (Post 308505)
ya certainly..... can u tell me the mesh details.....? and wht r ur inlet conditions......? if u pls let me know i would be able to help u....

i`m using unstructured mesh of tetrahedral volume on my rectangular domain. my inlet boundary condition was set to be a subsonic flow velocity with Cartesian velocity value. the turbulent intensity was 5%. my inlet was assign at left and bottom face. do you need more info pls tell me.

prshet May 21, 2011 02:54

ya thats alright....wht abt ur geometry.....? hw have u placed it.....? have u considered the whole geometry or only the half part (symmetry). and for different angle of attacks are u moving ur geometry.....?

icemaniac178 May 22, 2011 05:43

yes my geometry was taking the simplification of symmetrical condition (half part) and my angle of attack changes were determine by cartesian velocity components define at the inlet. i was not moving my geometry angle at all. what else i shoud do to get a good stall angle prediction?

prshet May 25, 2011 09:03

when u give the Cartesian velocity components it might give u comparable results for lower angle of attack. if u have to capture the stalling angle then it would be better if u manipulate the geometry itself....pls try once.... when u rotate the geometry please keep in mind the change in conditions for ur inlet velocity. this time u dont have to give the u and v components. u simply have to give the u component.

icemaniac178 May 29, 2011 19:31

i will look for forward to do it. thanks a lot. but do i need to switch into transient simulation for high AOA (17-20 degree) in order to capture better stall prediction? i have gone through a lot of discussion in this forum. many people suggest transient simulation for stalling prediction.

baserinia May 29, 2011 21:51

Quote:

Originally Posted by prshet (Post 298164)
but for analyzing a flutter problem for the airfoil i'll have to generate moving mesh.

Wing flutter is an example of fluid-structure interaction (FSI). You should look at the FSI tutorial in CFX help.


All times are GMT -4. The time now is 11:43.