# Getting lift force at zero angle of attack

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

 May 9, 2011, 10:00 Getting lift force at zero angle of attack #1 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 208 Rep Power: 11 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.

 May 9, 2011, 11:38 #2 Member   Charles Join Date: May 2011 Location: France Posts: 77 Rep Power: 8 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).

May 9, 2011, 11:41
#3
New Member

Nick
Join Date: May 2011
Posts: 4
Rep Power: 7
Quote:
 Originally Posted by 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.
I guess this is so small that you can regard it as zero. Do a couple of experiments and see if it fluctuates.

 May 9, 2011, 11:49 #4 Member   Charles Join Date: May 2011 Location: France Posts: 77 Rep Power: 8 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.

May 9, 2011, 12:00
#5
Member

Shenren Xu
Join Date: Jan 2011
Location: London, U.K.
Posts: 63
Rep Power: 8
Quote:
 Originally Posted by 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.
Could you post the mesh here?

It's very common to get non zero lift for zero alpha if your mesh if not symmetric.

 May 9, 2011, 12:56 #6 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 208 Rep Power: 11 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.

May 9, 2011, 13:05
#7
Member

Shenren Xu
Join Date: Jan 2011
Location: London, U.K.
Posts: 63
Rep Power: 8
Quote:
 Originally Posted by 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.
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.

 May 9, 2011, 13:29 #8 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 208 Rep Power: 11 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.

 May 9, 2011, 13:30 #9 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 208 Rep Power: 11 For cone cylinder I made a domain and then rotated it 360 to get the 3D blocks.

 August 3, 2012, 05:44 angle of attack #10 Senior Member   kunar Join Date: Nov 2011 Posts: 117 Rep Power: 7 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

 August 5, 2012, 03:27 Velocity profile in 3D #11 Senior Member   Shamoon Jamshed Join Date: Apr 2009 Location: Karachi Posts: 208 Rep Power: 11 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.

 August 6, 2012, 03:56 fluent doubt #12 Senior Member   kunar Join Date: Nov 2011 Posts: 117 Rep Power: 7 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,

August 7, 2012, 01:18
3D aerofoil simulation
#13
Senior Member

Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 208
Rep Power: 11
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 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,

 August 7, 2012, 02:25 fluent doubt #14 Senior Member   kunar Join Date: Nov 2011 Posts: 117 Rep Power: 7 Dear Shamoon Jamshed, thanks for your information.

 September 4, 2012, 15:52 #15 New Member   bhushan patil Join Date: May 2012 Posts: 19 Rep Power: 6 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

September 4, 2012, 23:16
#16
Senior Member

Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 208
Rep Power: 11
Quote:
 Originally Posted by p.bhushan2727@gmail.com 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. !!!!!!!!!!!!!!!!!!

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post hsieh Open Source Meshers: Gmsh, Netgen, CGNS, ... 32 September 13, 2011 05:50 toraya CFX 1 July 13, 2008 18:17 John Main CFD Forum 1 August 18, 2003 09:31 cfd_pro Main CFD Forum 1 August 23, 2002 17:21 cfd_pro FLUENT 0 August 23, 2002 16:16

All times are GMT -4. The time now is 11:02.