Hello All: I'm trying to model a 3D wing (.1m chord, .5m length, NACA 0009 at 5 degree angle of attack and 35.7 m/s) and having lots of problems getting any sort of reasonable data.

Meshing Procedure (GAMBIT):

1) Create the wing. 2) Create a sphere around the wing with a 2m radius. 3) Subtract the wing from the sphere. 4) Mesh the wing surfaces using a Tet/Pave scheme and small interval. 5) Mesh the outer sphere surface using a Tet/Pave scheme and large interval. 6) Mesh the volume using Tet/Hybrid and TGrid options.

The mesh is generates successfully and upon examining it, the highest Equiangle Skew is .81.

Solving Procedure (FLUENT):

1) Import the mesh. 2) Set the surface of the sphere to a pressure-far-field and the velocity vectors corresponding to a 5 degree angle of attack and the 35.7 m/s velocity. 3) Set the wing surface to wall, no slip. 4) Set the solver on coupled, implicit. 5) Set the viscous model to k-omega with default parameters - from what I've read, this seems like the one to use. 6) Material is air, constant density and viscosity. 7) Initialize, using the sphere surface as a reference. 8) Set up residual monitor. 9) Run 100 iterations to get lift and drag in the general area. 10) Set up lift and drag monitors 11) Run 200 more iterations.

At this point, the lift and drag coefficients make no sense at all. The lift coefficient is like 16000 where it should be .4 and the drag coefficient is -1500 where is should be .0233. Notice the drag coefficient is negative which makes no sense. If I look at contours of static pressure on the wing surface, it looks reasonable - higher pressure on the bottom than on the top. I also created a surface down the middle of my domain as a cross-section of the wing and velocity contours on this surface seems reasonable as well.

Anyone have any suggestions for me? I am reading drag and lift wrong or something?

Yes, you are reading "drag" and "lift" wrong. First of all, you need to give the correct reference values for velocity and areas (Use the menu items "Report --> Reference Values). This will now at least give you coefficients. Normal force and axial force coefficients, which Fluent in its wisdom insists on calling Lift and Drag. You have to convert NF and AF to Lift and Drag using the angle of attack.

I did do the Report ---> Reference values thing (I just selected the sphere surface as a reference). Should I be putting actual values in here? Now that I think about it, it seems like I should... When I do a report of forces, I put in a vector (of magnitude 1) that points in the direction of the force I'm looking for, either lift or drag, adjusted for the 5 degree angle. Is this what you mean or am I being a moron?

You do need to put in actual reference area (i.e. wing area), in the system of units that you are using. If you put in the right vector for the forces that should be OK.

[hhh]

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 chord '1'& extrude 100mm, in gambit and analysis in fluent i have doubt how to set velocity inlet, here i consider my velocity is 3m/s, then what is xyz component,please let me know.

2)if you consider 3D wing, (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

[veera]

Originally Posted by Charles
;114173

You do need to put in actual reference area (i.e. wing area), in the system of units that you are using. If you put in the right vector for the forces that should be OK.

hi i have one more questions in that field (reference values) in length and area always showing area= 1 m2 , length = 1m ,
but my qustions is , by your suggestions , i will put wing area in area , and what abouat length , here i have to give chord length ?
if yes means , i have swept back wing ..so two chord , which one i have to give