Problem with XFlow

GJimenez · July 13, 2015, 16:46

I'm trying to validate XFlow using the Validation Guide and i'm having problems with the NACA 0012.

The program gives me a CD over 1.5 and postprocessing Vorticity gives me this:
NACA0012.jpg

Near the wall gives me some vortex generating a lot of drag. I don't know how to get rid of them. I follow all the steps in the Validation Guide.

Can anyone help me with this?

Yplus · July 14, 2015, 12:36

Hi Gerardo,

From a quick look at your attached vorticity contours it looks like the number of points you are using to discretise the NACA0012 is not enough to give an accurate leading edge. This leads to a quite sharp LE and that explains the high vorticity regions you see. I would suggest to increase the number of points you are using when generating the airfoil in XFlow.

GJimenez · July 14, 2015, 13:33

Hi Giuseppe,

I used the Geometry generator from XFlow, I'll create the geometry in other CAD software and try it.

Thanks a lot!

GJimenez · July 14, 2015, 18:56

I'm having the same problem, now the CD is .74, still high.

I'm analyzing the NACA 0012 at Re 500.

With resolved scale of 2.56 m
Adaptive refinement
Target scale .005m
Wake REsolution .005m

I tried with a higher resolution (.01m) and the problem was lower.

FJSJ · August 3, 2015, 08:45

Hi Gerardo,

can you share your geometry and .xfp file? I will have a look!

Are you using convolution for visualizing? How many points are you using to define the NACA section? (I assume you are using Create NACA (4 digits) tool from XFlow)

GJimenez · August 12, 2015, 12:03

Quote:

Originally Posted by FJSJ

Hi Gerardo,

can you share your geometry and .xfp file? I will have a look!

Are you using convolution for visualizing? How many points are you using to define the NACA section? (I assume you are using Create NACA (4 digits) tool from XFlow)

Hi,

I had help from XFlow and my problem was solved, they send me the .xfp file.

But I tried with another airfoil and accidentally I put a Target resolved scale of .14 and the results where ok, but when I put the target at .005, the airfoil generate a lot of turbulence and a lot of errors.

Its bad to have a target as little as .005?

July 13, 2015, 16:46	Problem with XFlow	#1
GJimenez New Member Gerardo Jiménez Join Date: Feb 2015 Posts: 6 Rep Power: 11	I'm trying to validate XFlow using the Validation Guide and i'm having problems with the NACA 0012. The program gives me a CD over 1.5 and postprocessing Vorticity gives me this: NACA0012.jpg Near the wall gives me some vortex generating a lot of drag. I don't know how to get rid of them. I follow all the steps in the Validation Guide. Can anyone help me with this?

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July 14, 2015, 12:36		#2
Yplus New Member Giuseppe Trapani Join Date: Oct 2011 Posts: 1 Rep Power: 0	Hi Gerardo, From a quick look at your attached vorticity contours it looks like the number of points you are using to discretise the NACA0012 is not enough to give an accurate leading edge. This leads to a quite sharp LE and that explains the high vorticity regions you see. I would suggest to increase the number of points you are using when generating the airfoil in XFlow.

July 14, 2015, 13:33		#3
GJimenez New Member Gerardo Jiménez Join Date: Feb 2015 Posts: 6 Rep Power: 11	Hi Giuseppe, I used the Geometry generator from XFlow, I'll create the geometry in other CAD software and try it. Thanks a lot!

July 14, 2015, 18:56		#4
GJimenez New Member Gerardo Jiménez Join Date: Feb 2015 Posts: 6 Rep Power: 11	I'm having the same problem, now the CD is .74, still high. I'm analyzing the NACA 0012 at Re 500. With resolved scale of 2.56 m Adaptive refinement Target scale .005m Wake REsolution .005m I tried with a higher resolution (.01m) and the problem was lower.

August 3, 2015, 08:45		#5
FJSJ Senior Member Javi Join Date: Jan 2013 Posts: 276 Rep Power: 16	Hi Gerardo, can you share your geometry and .xfp file? I will have a look! Are you using convolution for visualizing? How many points are you using to define the NACA section? (I assume you are using *Create NACA (4 digits)* tool from XFlow)