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-   -   Modelling of a foil and comparison with NACA data (http://www.cfd-online.com/Forums/cfx/23388-modelling-foil-comparison-naca-data.html)

Tom December 7, 2006 07:39

Modelling of a foil and comparison with NACA data
 
Hi, i have designed and modelled a NACA 642-015 foil in ansys at 2 degrees and 14 degrees. the results for 2 degrees match up well for lift coefficient but not for drag? and again for the 14 degree foil lift and drag do match up to NACA values.

why is this, what floors are there in Ansys modelling such as modelling through seperated flow and turbulence effects. also does the program have difficulty calculating drag.

thaks alot for any responses!!!

Joe December 7, 2006 12:55

Re: Modelling of a foil and comparison with NACA d
 
Grid independance study?

Massive separation may make a RANS approach wobble at the knees.

Glenn Horrocks December 7, 2006 17:24

Re: Modelling of a foil and comparison with NACA d
 
Hi,

Also add to the list of things to check:

Laminar to turbulent transition, upstream effects, blockage factor, correct modelling of surface roughness, transient effects around the stall point, etc etc.

There are a lot of things which have to be right before you get an accurate airfoil simulation.

Glenn Horrocks

Tom December 8, 2006 13:25

Re: Modelling of a foil and comparison with NACA d
 
i was sort of wondering what were the differences between K-epsilon modeling, SST modeling and K-omega modelling and what were the advantages and disadvantages of using the different techniques.....

cheers again

Jonas Pedro Caumo December 9, 2006 15:07

Re: Modelling of a foil and comparison with NACA d *NM*
 

Jonas Pedro Caumo December 9, 2006 15:10

Re: Modelling of a foil and comparison with NACA d
 
you need to improve your mesh near the airfoil to get a good boundary layer calculation, because near the airfoil the gradient of velocity is very high, an O-grid is a good type of mesh, your turbulence model need to be good, have you ever tried sparlat-almaras ? Do you calculate y+ ? these things help to get accuracy. Thanks.


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