CFD validation on Eppler 473 airfoil and getting incorrect results

Willemsj · April 1, 2015, 18:42

I am running CFD validation on Eppler 473 airfoil at Re of 500,000. I am using pointwise for pre-processor and ANSYS Fluent for solver. I am using the SST transitional model, and using pressure far field, symmetry and wall boundary conditions. I am getting values that coincide with experimental data at zero degrees angle of attack, however my results at 5 degrees AoA and higher are incorrect. I should be getting cl=0.6 and cd = 0.012 and 5 degrees AoA. I am getting a cl of about 0.33 and cd values of about 0.021. My residuals and cl and cd monitors are well converged without oscillations and I am getting the same values using transitional and turbulent models. I know that my grid is very fine with a y+ value of about 2 and should be able to resolve the boundary layer.

If anyone has any idea for help please let me know.

dynamic · April 3, 2015, 10:09

Are you sure you have set the correct reference values for area, length and depth corresponding to the airfoil you are using?

Willemsj · April 3, 2015, 13:58

I'm pretty sure I am.

Its a 2-D airfoil problem but from the recommendation of my professor I've extruded 1 (one meter) cell thick in the z direction and am running it as a 3-D problem in fluent. In the reference conditions sections I have the reference area as 1 m2 and it is being computed from my inflow BC. The chord length of the airfoil is 1 m.

I've done plenty of analyses with airfoils and have gotten good results. Maybe its because i'm using a C-grid and in the past i've used an O-grid wind tunnel method? I've gotten good results at 0 AoA but at 5 and 10 degrees i'm getting wrong answers with c-grid.

dynamic · April 5, 2015, 08:05

Quote:

Originally Posted by Willemsj

I've gotten good results at 0 AoA but at 5 and 10 degrees i'm getting wrong answers with c-grid.

Will If you were getting good results at zero degrees, I would suggest checking your lift and drag monitors, how are you Pitching the foil? are you actually physically changing the foil or are you just changing the components of the foil? If you are only changing the components of the flow you have to take this into account in your lift and drag monitors to ensure they're always perpendicular and parallel to the flow respectively.

Willemsj · April 5, 2015, 17:59

For the c-grid I am making the incoming velocity components in the x y and z directions and adjusting for each angle of attack. Then in the monitors I am adjusting the cl and cd monitors by the angle of attack. With the cd vector perpendicular to the incoming flow and cl vector perpendicular to the flow.

For the o-grid in the past I have just rotated the actual circular o-grid.

April 1, 2015, 18:42	CFD validation on Eppler 473 airfoil and getting incorrect results	#1
Willemsj New Member Jon Willems Join Date: Apr 2015 Posts: 3 Rep Power: 11	I am running CFD validation on Eppler 473 airfoil at Re of 500,000. I am using pointwise for pre-processor and ANSYS Fluent for solver. I am using the SST transitional model, and using pressure far field, symmetry and wall boundary conditions. I am getting values that coincide with experimental data at zero degrees angle of attack, however my results at 5 degrees AoA and higher are incorrect. I should be getting cl=0.6 and cd = 0.012 and 5 degrees AoA. I am getting a cl of about 0.33 and cd values of about 0.021. My residuals and cl and cd monitors are well converged without oscillations and I am getting the same values using transitional and turbulent models. I know that my grid is very fine with a y+ value of about 2 and should be able to resolve the boundary layer. If anyone has any idea for help please let me know.

April 3, 2015, 10:09		#2
dynamic New Member Ronald Thompson Join Date: Mar 2015 Location: Portland, Oregon, USA Posts: 25 Rep Power: 11	Are you sure you have set the correct reference values for area, length and depth corresponding to the airfoil you are using? Willemsj likes this.

April 3, 2015, 13:58		#3
Willemsj New Member Jon Willems Join Date: Apr 2015 Posts: 3 Rep Power: 11	I'm pretty sure I am. Its a 2-D airfoil problem but from the recommendation of my professor I've extruded 1 (one meter) cell thick in the z direction and am running it as a 3-D problem in fluent. In the reference conditions sections I have the reference area as 1 m2 and it is being computed from my inflow BC. The chord length of the airfoil is 1 m. I've done plenty of analyses with airfoils and have gotten good results. Maybe its because i'm using a C-grid and in the past i've used an O-grid wind tunnel method? I've gotten good results at 0 AoA but at 5 and 10 degrees i'm getting wrong answers with c-grid.

April 5, 2015, 17:59		#5
Willemsj New Member Jon Willems Join Date: Apr 2015 Posts: 3 Rep Power: 11	For the c-grid I am making the incoming velocity components in the x y and z directions and adjusting for each angle of attack. Then in the monitors I am adjusting the cl and cd monitors by the angle of attack. With the cd vector perpendicular to the incoming flow and cl vector perpendicular to the flow. For the o-grid in the past I have just rotated the actual circular o-grid.