[GDS]

I am trying to run a "2D" case with a multi-element airfoil: a single element in the z-axis and the profile extruded to a depth of 1.0. I want to compare Cl and Cd with some published results, but I am not sure what to use for the reference area. The main airfoil and the flap overlap, and the flap is angled w.r.t. the main airfoil chord. The total chord of the two airfoils is greater than 1.0.

[shereez234]

Originally Posted by GDS

I am trying to run a "2D" case with a multi-element airfoil: a single element in the z-axis and the profile extruded to a depth of 1.0. I want to compare Cl and Cd with some published results, but I am not sure what to use for the reference area. The main airfoil and the flap overlap, and the flap is angled w.r.t. the main airfoil chord. The total chord of the two airfoils is greater than 1.0.

Usually for multi-element airfoils stowed chord is the right way to go.
Why don't you try to find the reference length from journal paper/s about this airfoil?

An alternative is to find the pressure coeff, Cp distribution graphs in the journal paper which will give you an idea of the reference lengths.

And the reference length for a simple airfoil is Cref_airfoil*depth (in 2d) for OpenFOAM.

[GDS]

Thanks for the reply, but I am a little confused when you say "reference length". I thought that was used for moment calculations. Did you mean "area"?


The only paper I have been able to access that has wind tunnel data has only Cp distributions and no force data, so there is no reference area/length given. The max x/c in the plots is about 1.2, which is about what the maximum x value is in the airfoil data file.

[shereez234]

Originally Posted by GDS

Thanks for the reply, but I am a little confused when you say "reference length". I thought that was used for moment calculations. Did you mean "area"?


The only paper I have been able to access that has wind tunnel data has only Cp distributions and no force data, so there is no reference area/length given. The max x/c in the plots is about 1.2, which is about what the maximum x value is in the airfoil data file.

Correct me if I am wrong but in 2D, the reference length is the reference area for airfoil. ( In OpenFOAM this value gets multiplied by the extrusion depth i.e. how far your empty front and back planes are).

Have a look at how it was done for 30P30N multi-element airfoil in this paper, see Table 1.

https://research-information.bris.ac.../30P30N_LT.pdf