# just a question about airfoil (Turbolence model and Cd)

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 March 31, 2000, 09:09 just a question about airfoil (Turbolence model and Cd) #1 Maria Teresa Milesi Guest   Posts: n/a Sponsored Links Dear all, I'm studying an airfoil (NACA631412), but I've no agreement between my results and the wind-tunnel data. My problem is: -Cl is near to the sperimental value but Cd is higher than the sperimental one (sperim:0.0055; mine:0.011); I use K-e realizable model with non-equilibrium wall functions (I=0.1%;viscosity-ratio=10). My mesh is hybrid: orthogonal in the boundary layer and triangular away (domain is about 20 chords lenght and 10 chords high). Can you help me? Do you think I've chosed the right model and the right turbolent's values to put in the boundary conditions? Thanks for all Maria Teresa

 March 31, 2000, 10:22 Re: just a question about airfoil (Turbolence model and Cd) #2 John C. Chien Guest   Posts: n/a (1). Currently, no code on earth can predict the right Cd value of an airfoil. (2). You can select other options and check the results. (3). CFD is not yet good enough to predict the integrated global parameters. It is mainly used to study the detailed physics of the flow. If you can get the Cl and Cd right, then the solution is exact everywhere, which is not possible right now. (4). Please stop day dreaming about getting the right Cd of airfoil.

 April 7, 2000, 09:56 Re: just a question about airfoil (Turbolence model and Cd) #4 Dario Pinelli Guest   Posts: n/a Ciao Maria Teresa, per la mia piccola esperienza...ho fatto una tesi sulla resistenza di attrito aerodinamico su un profilo NACA0012 con Fluent...il problema principale sta nella discretizzazione dello strato limite...devi arrivare ad una mesh molto fine.... ...per quanto riguarda il modello di turbolenza io li ho provati tutti...anche la LES!!!! ma alla fine ho scelto lo standard k-epsilon con standard wall-function perche' non si ottenevano risultati migliori...ma almeno dava tempi di soluzione piu' ragionevoli! ...adesso non posso darti altre informazioni perche sono a lavoro...se vuoi ti mando un po' di risultati. Ciao Dario

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