CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Getting lift force at zero angle of attack

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   May 9, 2011, 10:00
Default Getting lift force at zero angle of attack
  #1
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Hi,

I am modelling a simple NACA 0012 aerofoil at zero alpha but I am getting lift force at even zero angle of attack. Why is it so? Lift coefficient is under e-06.
Shamoon Jamshed is offline   Reply With Quote

Old   May 9, 2011, 11:38
Default
  #2
Member
 
Charles
Join Date: May 2011
Location: France
Posts: 78
Rep Power: 6
Santos-Dumont is on a distinguished road
Hi,

It's normal, most of the airfoils get a zero lift at around -2. Check your profile's polar to find out (look for the "Theory of Wing sections" .pdf on the Internet).
Santos-Dumont is offline   Reply With Quote

Old   May 9, 2011, 11:41
Default
  #3
New Member
 
Nick
Join Date: May 2011
Posts: 4
Rep Power: 6
Unneoetech is on a distinguished road
Quote:
Originally Posted by Shamoon Jamshed View Post
Hi,

I am modelling a simple NACA 0012 aerofoil at zero alpha but I am getting lift force at even zero angle of attack. Why is it so? Lift coefficient is under e-06.
I guess this is so small that you can regard it as zero. Do a couple of experiments and see if it fluctuates.
Unneoetech is offline   Reply With Quote

Old   May 9, 2011, 11:49
Default
  #4
Member
 
Charles
Join Date: May 2011
Location: France
Posts: 78
Rep Power: 6
Santos-Dumont is on a distinguished road
Correction, NACA 0012 gets 0 lift at 0.
But if the Cl your calculate is at an order as low as 10^-6, you can consider it as zero.
Santos-Dumont is offline   Reply With Quote

Old   May 9, 2011, 12:00
Default
  #5
Member
 
Shenren Xu
Join Date: Jan 2011
Location: London, U.K.
Posts: 63
Rep Power: 6
Shenren_CN is on a distinguished road
Quote:
Originally Posted by Shamoon Jamshed View Post
Hi,

I am modelling a simple NACA 0012 aerofoil at zero alpha but I am getting lift force at even zero angle of attack. Why is it so? Lift coefficient is under e-06.
Could you post the mesh here?

It's very common to get non zero lift for zero alpha if your mesh if not symmetric.
Shenren_CN is offline   Reply With Quote

Old   May 9, 2011, 12:56
Default
  #6
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
So you mean that its all because of mesh! Guys I told you that my problem is caused by the Force not the coefficient. I also get the same for a problem of cone cylinder assembly whose mesh size is 0.4 million. Still its symmetry of the grid issue? Lift force 55 N while coefficient 1e-4.
Shamoon Jamshed is offline   Reply With Quote

Old   May 9, 2011, 13:05
Default
  #7
Member
 
Shenren Xu
Join Date: Jan 2011
Location: London, U.K.
Posts: 63
Rep Power: 6
Shenren_CN is on a distinguished road
Quote:
Originally Posted by Shamoon Jamshed View Post
So you mean that its all because of mesh! Guys I told you that my problem is caused by the Force not the coefficient. I also get the same for a problem of cone cylinder assembly whose mesh size is 0.4 million. Still its symmetry of the grid issue? Lift force 55 N while coefficient 1e-4.
All that I was saying is that it's very likely it's caused by the mesh. And it's so simple to test if it's true. Simple take a symmetric mesh and see what number you get. Force or coefficient, are they the same thing?...

And you problem is not CAUSED by the force; instead, the "wrong" force is telling you there might be a problem.
Shenren_CN is offline   Reply With Quote

Old   May 9, 2011, 13:29
Default
  #8
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
I am sorry I didnt get your point. What do you mean by the wrong Force? For Normal force (or Lift at 0 alpha) coefficient I give the vector 0 1 0 in Fluent.
Shamoon Jamshed is offline   Reply With Quote

Old   May 9, 2011, 13:30
Default
  #9
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
For cone cylinder I made a domain and then rotated it 360 to get the 3D blocks.
Shamoon Jamshed is offline   Reply With Quote

Old   August 3, 2012, 05:44
Default angle of attack
  #10
hhh
Senior Member
 
kumar
Join Date: Nov 2011
Posts: 115
Rep Power: 5
hhh is on a distinguished road
Dear friends,
In fluent, For analysis of 2D naca0012 airfoil velocity inlet we give vcostheta in x component & vsintheta in y component, v is inlet velocity.

1)here i start analysis of 3D wing, for that i take naca 0012 airfoil & extrude 100mm, in gambit and analysis in fluent i have doubt how to set velocity inlet, here i consider my velocity is 50m/s, then what is xyz component,please let me know.

2)if you consider 3D wing what is z component(vtantheta for z component) is correct or wrong, please let me know.

2) how to find angle of attack for 3D wing? please let me know
hhh is offline   Reply With Quote

Old   August 5, 2012, 03:27
Default Velocity profile in 3D
  #11
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
In 3D even if you had taken the velocity inlet as the front end boundary condition you will need to specify 2D components of velocity i.e. x and y components. The third component in z direction would be zero. However, if you are certain that there is some third component and the velocity is not uniform you must need to provide data for all the three components of velocity at inlet through Define---> Profiles.
Shamoon Jamshed is offline   Reply With Quote

Old   August 6, 2012, 03:56
Default fluent doubt
  #12
hhh
Senior Member
 
kumar
Join Date: Nov 2011
Posts: 115
Rep Power: 5
hhh is on a distinguished road
Dear Shamoon Jamshed,
thanks for your kind response, i take 2D naca0012 airfoil & and make 3D wing for that i extrude 100mm and meshed in gambit.my boundary conditions are velocity inlet,pressure outlet,remaining all are symmetry, and the wall(stationary) is wing. In fluent how i give all the parameters, to find lift and drag for my 3D wing, my velocity is 10m/s.


if u don't mind, please give the details step by step in fluent& please let me know.
step1--define-solver
step2--define--BC ......like that, i hope its only 10-15 steps up to iteration,
hhh is offline   Reply With Quote

Old   August 7, 2012, 01:18
Default 3D aerofoil simulation
  #13
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Quite surprising that you are asking each and every bit although you know 2D. Anyway, the procedure is no different than 3D. Just define the velocity inlet all over the far-field domain (vel inlet=pr far field in case of supersonic flow). Now define the x and y components ( I assume the wing span in x z plane) of the velocity in velocity inlet bc. Select magnitude and components. Go to solve ---> monitors ---> Drag and solve ---> monitors ---> Lift and click on write and plot so that you can view the results of Cd and Cl whether converged or not. Before this set reference values of area as unit chord length(or if you have any specific value from experiment). Then run the iterations.


Quote:
Originally Posted by hhh View Post
Dear Shamoon Jamshed,
thanks for your kind response, i take 2D naca0012 airfoil & and make 3D wing for that i extrude 100mm and meshed in gambit.my boundary conditions are velocity inlet,pressure outlet,remaining all are symmetry, and the wall(stationary) is wing. In fluent how i give all the parameters, to find lift and drag for my 3D wing, my velocity is 10m/s.


if u don't mind, please give the details step by step in fluent& please let me know.
step1--define-solver
step2--define--BC ......like that, i hope its only 10-15 steps up to iteration,
Shamoon Jamshed is offline   Reply With Quote

Old   August 7, 2012, 02:25
Default fluent doubt
  #14
hhh
Senior Member
 
kumar
Join Date: Nov 2011
Posts: 115
Rep Power: 5
hhh is on a distinguished road
Dear Shamoon Jamshed,

thanks for your information.
hhh is offline   Reply With Quote

Old   September 4, 2012, 15:52
Default
  #15
New Member
 
bhushan patil
Join Date: May 2012
Posts: 19
Rep Power: 5
p.bhushan2727@gmail.com is on a distinguished road
Dear
Shamoon Jamshed,
i am doing aerofoil simultion in fluent using aateched tutorail but my soln is not conversed...in that.whatthe problem i dont get...even 50 thosan itaration has over....sry i cant able attached ithe tutorail....will u please find it from google as aeofoil tutorail
p.bhushan2727@gmail.com is offline   Reply With Quote

Old   September 4, 2012, 23:16
Default
  #16
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 114
Rep Power: 8
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Quote:
Originally Posted by p.bhushan2727@gmail.com View Post
Dear
Shamoon Jamshed,
i am doing aerofoil simultion in fluent using aateched tutorail but my soln is not conversed...in that.whatthe problem i dont get...even 50 thosan itaration has over....sry i cant able attached ithe tutorail....will u please find it from google as aeofoil tutorail
Lot of tutorials can be searched on google. !!!!!!!!!!!!!!!!!!
Shamoon Jamshed is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Import netgen mesh to OpenFOAM hsieh Open Source Meshers: Gmsh, Netgen, CGNS, ... 32 September 13, 2011 05:50
Lift at zero angle of attack toraya CFX 1 July 13, 2008 18:17
Plotting of lift coefficient vs angle of attack?? John Main CFD Forum 1 August 18, 2003 09:31
Lift Coefficient Vs. Angle of Attack cfd_pro Main CFD Forum 1 August 23, 2002 17:21
Lift Coefficien Vs. Angle of Attack cfd_pro FLUENT 0 August 23, 2002 16:16


All times are GMT -4. The time now is 03:24.