I am getting poor solutions - input error?

williambwright · November 10, 2016, 17:42

I am running a 2D airfoil at 12° AOA and the solution I get is nowhere near stall even though I should be past the stall angle. I'm trying to figure out where the error is in the input file and I don't see it. The grid file is non-dimensionalized by chord (0.4572 m). I have attached the cfg file and would appreciate any suggestions. I am using version 4.0.0 with SST turbulence model

nomad2 · November 14, 2016, 16:18

Hi William, did you do a grid refinement? And what are you comparing your results to?

williambwright · November 15, 2016, 10:41

I did a grid refinement without a change. I am comparing to exp. data which shows stall at 8° whereas the lift curve is still linear at 12°. I'm looking for something wrong in the boundary condition or some other setting that would explain this. The grid is unstructured, but I used a function in Pointwise called T-Rex to put structured grid near the wall and have y+ =1. For what it is worth, the computed lift is low even in the linear part of the curve. I'm thinking of running the higher AOAs unsteady but I wanted to see if I had anything obviously set up wrong

nomad2 · November 15, 2016, 13:02

Thanks for the info.

Pointwise has the tendency to pinch the prism layer near the leading and trailing edges. At higher alphas, the flow boundary layer tends to be much thicker at the trailing, such that it will be outside the pinched prism layers, and in the coarser isotropic region.

Do you have an image of the mesh?

williambwright · November 15, 2016, 14:42

Far field and near field attached. Outer boundary is an O-grid at 20 chord lengths
I can keep going with grid refinement, but I think I should see what happens with going unsteady

nomad2 · November 15, 2016, 15:01

That's an unusual looking thing.

There are substantial flow gradients near the leading edge which is not immersed in a refined mesh. I suspect your refinement region would need to extend further upstream to capture that.

If the unsteady run doesn't give what you want, try a refinement box around the entire airfoil, extending about 0.25c all around.

November 10, 2016, 17:42	I am getting poor solutions - input error?	#1
williambwright New Member William Wright Join Date: Apr 2015 Posts: 8 Rep Power: 10	I am running a 2D airfoil at 12° AOA and the solution I get is nowhere near stall even though I should be past the stall angle. I'm trying to figure out where the error is in the input file and I don't see it. The grid file is non-dimensionalized by chord (0.4572 m). I have attached the cfg file and would appreciate any suggestions. I am using version 4.0.0 with SST turbulence model

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[OpenFOAM.org] Compile OF 2.3 on Mac OS X .... the patch	gschaider	OpenFOAM Installation	225	August 25, 2015 19:43
Errors in UDF	shashank312	Fluent UDF and Scheme Programming	6	May 30, 2013 20:30
How to install CGNS under windows xp?	lzgwhy	Main CFD Forum	1	January 11, 2011 18:44
ParaView for OF-1.6-ext	Chrisi1984	OpenFOAM Installation	0	December 31, 2010 06:42
[swak4Foam] groovyBC: problems compiling: "flex: not found" and "undefined reference to ..."	sega	OpenFOAM Community Contributions	12	February 17, 2010 09:30

November 14, 2016, 16:18		#2
nomad2 New Member California Join Date: Nov 2016 Posts: 10 Rep Power: 9	Hi William, did you do a grid refinement? And what are you comparing your results to?

November 15, 2016, 10:41		#3
williambwright New Member William Wright Join Date: Apr 2015 Posts: 8 Rep Power: 10	I did a grid refinement without a change. I am comparing to exp. data which shows stall at 8° whereas the lift curve is still linear at 12°. I'm looking for something wrong in the boundary condition or some other setting that would explain this. The grid is unstructured, but I used a function in Pointwise called T-Rex to put structured grid near the wall and have y+ =1. For what it is worth, the computed lift is low even in the linear part of the curve. I'm thinking of running the higher AOAs unsteady but I wanted to see if I had anything obviously set up wrong

November 15, 2016, 13:02		#4
nomad2 New Member California Join Date: Nov 2016 Posts: 10 Rep Power: 9	Thanks for the info. Pointwise has the tendency to pinch the prism layer near the leading and trailing edges. At higher alphas, the flow boundary layer tends to be much thicker at the trailing, such that it will be outside the pinched prism layers, and in the coarser isotropic region. Do you have an image of the mesh?

November 15, 2016, 15:01		#6
nomad2 New Member California Join Date: Nov 2016 Posts: 10 Rep Power: 9	That's an unusual looking thing. There are substantial flow gradients near the leading edge which is not immersed in a refined mesh. I suspect your refinement region would need to extend further upstream to capture that. If the unsteady run doesn't give what you want, try a refinement box around the entire airfoil, extending about 0.25c all around.