topic Re: How to calculate drag coefficient of wing? in CFD Forum

How to calculate drag coefficient of wing?

Anonymous — Fri, 22 Mar 2019 04:55:06 GMT

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-coefficient-drag-urbee-example.html

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.

Re: How to calculate drag coefficient of wing?

frederic.gaillard.7 — Fri, 22 Mar 2019 13:10:31 GMT

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

Re: How to calculate drag coefficient of wing?

frederic.gaillard.7 — Fri, 22 Mar 2019 13:57:50 GMT

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

Re: How to calculate drag coefficient of wing?

frederic.gaillard.7 — Fri, 22 Mar 2019 18:05:55 GMT

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

Re: How to calculate drag coefficient of wing?

Anonymous — Sun, 24 Mar 2019 17:23:30 GMT

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

Re: How to calculate drag coefficient of wing?

frederic.gaillard.7 — Sun, 24 Mar 2019 17:27:23 GMT

Hello @Anonymous ,

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

Re: How to calculate drag coefficient of wing?

frederic.gaillard.7 — Mon, 25 Mar 2019 13:25:53 GMT

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

Good luck
Fred

Re: How to calculate drag coefficient of wing?

frederic.gaillard.7 — Mon, 25 Mar 2019 13:29:21 GMT

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

Good luck
Fred

Re: How to calculate drag coefficient of wing?

Anonymous — Mon, 25 Mar 2019 13:49:04 GMT

Thank you!