How to calculate drag coefficient of wing?

[Anonymous]

Hello. I try to calculate drag coefficient of a regular 3D wing. But in result I got value - 0.56. I think this is a very huge value for wing.

Wikipedia says that whole Cessna 182 have Cd = 0.027: https://en.wikipedia.org/wiki/Drag_coefficient#Aircraft

For calculating I use tutorial and formula published here https://knowledge.autodesk.com/support/cfd/learn-explore/caas/simplecontent/content/calculating-the-...

My parameters for formula:

Force by direction 380 Newton;

Velocity 50 m/s

Cross sectional area 0.45 m2

Air density 1.2

Please, review my model located here https://drive.google.com/file/d/1uwAfzZR1i6F6BaviWUa09O--xCsmIG-U/view?usp=sharing and tell me what I am doing wrong.

[frederic.gaillard.7]

Hello @Anonymous , 

Your mesh is clearly too coarse! And you will more than 3 boundary layer for this kind of analysis. 
Try to refined your model first and foremost
Fred

[frederic.gaillard.7]

Is there any specific reason to operate in a compressible environment ?

[frederic.gaillard.7 · Accepted solution]

Hello @Anonymous , 

Few thing to enhance your result. 

1. You should simulate your model in 2D instead. The computational cost of a 3D model is too high. By doing this you will be able to allocate a lot more element in your 2D model which is responsible for an accurate simulation

2. Choose a SST-kw turbulence model instead of the k-epsilon

3. Switch to incompressible. Compressible analysis is more suitable for high speed velocity and necessite unknown boundary condition instead of a 0 pressure gage.  Your BC are perfectly set for an incompressible analysis, good job !

4. Supress the mesh from your wing. your simulation will solve faster ! 

5. Add extra boundary layer near of your wing (5 -10) and make sure that your Y+ values had a correct value.  With a SST model Y+ should be around 1, with the k-epsilon Y+ should lie between 35 and 350. 

Up : Your simulation
Below  : SST-kw - 5 boundary layer 

velocity profile

Up : Your simulation
Below  : SST-kw - 5 boundary layer 

You see a tremendous difference in the result with just a simple refined meshing. 
Good Luck 

[Anonymous]

Fred. Thanx for explanation. Would you share your setup? I would like to study on it.

[frederic.gaillard.7]

Hello @Anonymous , 

Yes absolutely, i will send it to you monday morning. 
Fred

[frederic.gaillard.7]

here is the CFZ and a tutorial that can help 
https://www.youtube.com/watch?v=N4z8HcBtL6U

Good luck 
Fred

[frederic.gaillard.7 · Accepted solution]

here is the CFZ and a tutorial that can help 
https://www.youtube.com/watch?v=N4z8HcBtL6U

Good luck 
Fred

[Anonymous]

Thank you!