Low Reynolds Number

isaac1326 · September 24, 2014, 21:22

Hi,
Im doing a CFD analysis on a NACA 0012 wing, with a AR of 5.0 at a Re number of 80000. I am validating it with an experimental data. Im still unsure which model I have to be using , whether to go with laminar or use turbulent BL. When I have used , laminar model, the lift coefficients matched, but the drag coefficients are far way off.
Experimental @ 5 degrees
Cl - 0.4, cd -0.12.
My analysis
Cl -0.38, cd -0.06.
Any help in helping me solve this, is deeply appreciated

Alfalfa · September 28, 2014, 20:28

I guess you could use a low-Reynolds Turbulence model such as k-omega sst. Those are usually good for external aero purpose. That being said, in my experience I've found that it's always hard to match the drag values.

isaac1326 · September 29, 2014, 02:30

Iv tried that too, Iv played with the turbulence intensity and viscosity ratio too, still no avail , is there a limiting factor for Tu?

me3840 · September 29, 2014, 17:50

What does your grid look like? That's more than likely the problem.

lcarasik · September 29, 2014, 18:04

Could the Turbulence Suppression model help in this problem?

isaac1326 · October 1, 2014, 14:21

Quote:

Originally Posted by me3840

What does your grid look like? That's more than likely the problem.

I have 300 grid points on the airfoil, and y+ = 0.8,
Regarding the grid, my only question, shd i keep dropping the y+ value, to see if my results would get any better?

isaac1326 · October 1, 2014, 14:22

Quote:

Originally Posted by lcarasik

Could the Turbulence Suppression model help in this problem?

Yes, i have used Turbulence Suppression Model, but the answers still did not change. I am running this simulation in Star CCM+, and i used, SA model, and tried playing with turbulence viscosity ratio, the Cd value increased to 0.89, but I didnt see any major changes,

me3840 · October 1, 2014, 16:45

You're doing LES for this?

isaac1326 · October 2, 2014, 10:29

Quote:

Originally Posted by me3840

You're doing LES for this?

I am doing RANS for this

me3840 · October 2, 2014, 12:10

I thought the turbulent suppression model was for LES.

Anyway, can you show me the grid?

isaac1326 · October 3, 2014, 00:27

Quote:

Originally Posted by me3840

I thought the turbulent suppression model was for LES.

Anyway, can you show me the grid?

http://www.4shared.com/folder/prFsZuQ1/_online.html

me3840 · October 4, 2014, 17:48

Your near-wall layers seem to be really coarse. What is your wall y+?

isaac1326 · October 4, 2014, 22:10

I have kept it as 0.5

shashankshankar · June 9, 2018, 05:12

hello Isaac
we're you able to resolve?
in my case drag coefficient is captured with minimal error of 1-3% whereas lift coefficient is way off. any help or suggestions please

September 24, 2014, 21:22	Low Reynolds Number	#1
isaac1326 New Member Isaac Join Date: Feb 2013 Posts: 27 Rep Power: 13	Hi, Im doing a CFD analysis on a NACA 0012 wing, with a AR of 5.0 at a Re number of 80000. I am validating it with an experimental data. Im still unsure which model I have to be using , whether to go with laminar or use turbulent BL. When I have used , laminar model, the lift coefficients matched, but the drag coefficients are far way off. Experimental @ 5 degrees Cl - 0.4, cd -0.12. My analysis Cl -0.38, cd -0.06. Any help in helping me solve this, is deeply appreciated

June 9, 2018, 05:12	same problem different issues	#14
shashankshankar New Member Join Date: Mar 2012 Posts: 12 Rep Power: 14	hello Isaac we're you able to resolve? in my case drag coefficient is captured with minimal error of 1-3% whereas lift coefficient is way off. any help or suggestions please

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September 28, 2014, 20:28		#2
Alfalfa New Member Gabriel Boucher Join Date: Jul 2013 Posts: 23 Rep Power: 12	I guess you could use a low-Reynolds Turbulence model such as k-omega sst. Those are usually good for external aero purpose. That being said, in my experience I've found that it's always hard to match the drag values.

September 29, 2014, 02:30		#3
isaac1326 New Member Isaac Join Date: Feb 2013 Posts: 27 Rep Power: 13	Iv tried that too, Iv played with the turbulence intensity and viscosity ratio too, still no avail , is there a limiting factor for Tu?

September 29, 2014, 17:50		#4
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	What does your grid look like? That's more than likely the problem.

September 29, 2014, 18:04		#5
lcarasik Senior Member Lane Carasik Join Date: Aug 2014 Posts: 692 Rep Power: 14	Could the Turbulence Suppression model help in this problem?

October 1, 2014, 16:45		#8
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	You're doing LES for this?

October 2, 2014, 12:10		#10
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	I thought the turbulent suppression model was for LES. Anyway, can you show me the grid?

October 4, 2014, 17:48		#12
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	Your near-wall layers seem to be really coarse. What is your wall y+?

October 4, 2014, 22:10		#13
isaac1326 New Member Isaac Join Date: Feb 2013 Posts: 27 Rep Power: 13	I have kept it as 0.5