[Polymont]

Hello everyone !!

So I'm trying to compare the performance of different wing for a kitefoil. Actually i'm using a 3D model of EPPLER 81, made with catia with the airfoiltools coordonates. It's simple an extrusion of the 2D profile nothing fancy for now.

-Chord 200mm and wing lenth 0.5m. (1m but symmetry in the middle).
-In water at 5m/s and 0° angle of attack at 15°C. My Reynolds number is around 800 000.
-Mesh in poly-hexcore, 3 millions elements, and my Y+ around the wing is <1 (juste a very small point on side where it's at 3)

My problems are : I tried a loooot (k omega, k omega SST, k epsilon, k kl omega, SST transition) of different combinaison with different mesh (yes i made sure i get the right Y+ each time), and I always have some pretty poor performance :
Lift = 330-360N range
Drag = 15-25N range
And what bother me the most is my Cl and my Cd in my repport definiton are crazy high like 550 for Cl and 30 for Cd. When I make my own calculation with the Drag and lift given by the repport i get 0.01 and 0.3.

My questions are :
-How do i get the rigth Cd and Cl in the repport definition ?
-Are my results absolut crap or make any sense ? (appart from cd and cl)
-The result I get is the for half wing right ? Even is there's a symmetry ?

My residuals are good for xyz velocity, K and omega it's difficult to get them below 10e-4 and continuity is a yoke, like 10e-2. The initialisation method seems to have the most impact on the residuals.

I'm new in the bothe... beautifull world of CFD so maybe there's something idk

[ngoctm]

Hi Polymont,

Please note that the reference values (Reference Values Task Page) are used to non-dimensionalize the forces and moments acting on the airfoil. The dimensionless forces and moments are the lift, drag, and moment coefficients.

Perhaps you need to consider the area in the calculations.

Area: sets the reference area, which is used to compute the force and moment coefficients.



Hope this help,