CFD - What in the hell...

I forgot to mention the last time, another integral part of making good use of FEA/CFD is being able to interpret the results properly. Easier said than done for someone whose background is in big billet aluminum pieces, tires, and suspension.

So I figured I'd play with some CFD with a stock airfoil profile. Not knowing what kind of camber, thickness, and AoA is appropriate, I took a random guess. Used an inverted NACA7412, a crapload of AoA, and a 25 m/s (~55mph) inlet velocity boundary condition. Boundary conditions for the top and bottom of the mesh are dU/dn = 0, and V = 0, with outlet being some extrapolated pressure.

Kinematic viscosity 2.59e-5 (a bit high for air I later remembered)

Since I'm ultimately interested in downforce and drag, I decided to look at pressure after my model ran for a bit.

Results sucked!

What in the hell is that shit? Pressure balls floating off my airfoil? Is that real? Wtf? Even as a tire engineer I have some sense to know that's probably not good.

Upon closer examination of the velocity field...


Kinda looks like flow separation. Or at least that's my guess. Major league flow separation. Like whoa. Edit - That looks like a typical von Karman vortex sheet now that I think about it... at least in the velocity view. Had never looked at pressure before!

I'm just playin' around for now, have to figure out how to grab cL and cD from these, but after some experimentation maybe this airfoil is a bit aggressive for the application (at least unmodified with no slats, flaps, Gurneys, etc)! I think this one below I even ran at at more proper viscosity of 1.59e-5


To be continued... later tonight.