Learning Forum

[aryaman.sudhir]

I am simulating the Naca 0012h airfoil at many AOAs, for now just 10 degrees. I am simulating both lift and drag, and getting the cl and cd from those values. However my Cl and Cd values are way of, i believe my Cl should be 1.2, however I am getting a value of .2. My fluid velocity is 30m/s, chord is 1m, and winspan is .5, however I am using symmetry. The lift value I am getting is around 27-29N, and with symmetry that makes 54-58N, which results in a low Cl. I am new to Ansys, and I have been looking at videos online to find different ways I can make my simulation better, but everytime I do change something, I still get the same lift values, I have tried Spalart alIarmas, Transition SSt, with y+ of around 1. appreciate any help!!. 

 

These are my meshes

[Rob]

Have a careful look at how the coefficients are defined. Then review the NACA tutorial/example in Fluent's Help to understand what you didn't set and how to alter those values. What are the outer surface boundary conditions?

[aryaman.sudhir]

Dear Rob, 

My boundary conditions are: inlet for the front which is velocity, outlet, in the back which is pressure, and then the side with the airfoil as symmetry, and the top, bottom, and other side wall as wall. I just watched another video, and saw the person make all the walls, top bottom, and side, as symmetry, so I will try that now. Thank you for your help !!

[aryaman.sudhir]

So my previous attempt did not work, however i tried again with transition SST, and got a much higher lift force of 56 N, with symmetry so total would be 112N. However this results in a Cl of .4, which is still less than half of what this should be, I read that for these types of tests done by actual organizations, the wings span the entire domain, so i will try that next.

[Rob]

Also look at the pressure on the top and bottom surfaces. You may need to adjust the range to see a peak somewhere around the blades. Then read up on wind tunnels and why they're calibrated. 

[aryaman.sudhir]

Hi Mr, Rob, I read about why wind tunnels are calibrated, and what I found was they are calibrated to compensate for the small errors that form due to the wind tunnel. So are you saying i should change my settings to compensate the errors formed by things such as my boundaries, etc.? Also Here is a picture of my pressure.

[Rob]

No, that you need to make the domain bigger. Focus on the darker orange contour that is the upstream colour that then passes beyond the lower side of the airfoil. Why does the pressure change beyond the air foil when there's no resistance to the flow? In 2d plot pressure on top & bottom edges with length. 

[aryaman.sudhir]

I increased the domain a lot, and there is no pressure change after the fluid passes the airfoil, however my force is still innacurate. I also realized that my y+ might be to high, so i went to results - xy plot- turbulence - wall Plus, and then clicked win and I got the graph below, I also attached my new pressure diagram.

[Rob]

You'll want to create a line on the wing - you've plotted all of the facet data. Not meeting the y+ criteria won't help, but reference values tend to dominate the coefficients. 

[aryaman.sudhir]

Dear Mr. Rob, I apologize but i dont quite understand what your are trying to say about the line on the wing. Are you saying for the y+ chart, instead of choosing the entire airfoil, which is what i did using named selections, is should use just a single line, for example the edge? I tried using the edge, but I could not select it for the y+ graph. Also, my reference values are correct, but do they affect the simulation? My force are incorrect even with correct reference values, so the coefficients will anyways be incorrect as well. 

Thank You for being so patient with me, Im very knew with the software, is started maybe 1 month or 2 ago. :)

Thank you,

Aryaman

[Rob]

In a 3d model plotting on the whole surface is good for contours etc but not overly useful for xy plots as you can see. And something we prepared earlier.... https://innovationspace.ansys.com/knowledge/forums/topic/how-do-i-create-a-line-on-a-curved-surface-wall/  

[aryaman.sudhir]

I read the information in the link, and im trying to create the iso surface but its just not working for me, I click turbulence, then Wally+ and for surfaces i click airfoil, then create, but it says no surfaces selected.

 

Thank You,

Aryaman