Movable trailing edge flaps implementation

Hello Xiao,
Thank you very much. This tool is very handy.

Hello Xiao,
I have used the XFLR5 to generate the airfoil coefficients with flap. I have used the coordinates of the airfoil provided in the FAST 5MW wind turbine. For example I have loaded the DU21_A17 airfoil coordinates with Reynolds number = 0.75E6. I have not found anything else to change. I have generated the polar for zero flap angle(same as the normal polar already given by FAST for the airfoil DU21_A17). However, the output polar coefficients are different to the original polar available. I would like to know if the deviation is due to the limited inputs I have given (only Reynolds number) or the accuracy of the software itself is less?


Dear Chaitanya,

I can’t comment on the XFLR5 tool, but you should be aware that the airfoil polars for the blades of the NREL 5-MW turbine in the FAST archive include the influence of 3D corrections, including corrections for rotational augmentation (stall delay) and deep-stall drag (Viterna). Please see Section 3 of the NREL 5-MW specifications report for more information:

Best regards,

Dear Majjari,

The XFOIL is based on the planar flow theory if I remember correctly.
The accuracy is limited. For a more accurate estimation, I would use CFD.

It is also good to start with a clean airfoil to calibrate your flow simulation model.
For XFLR5, you can play with different Reynolds number, Mach number and Ncrit. Then adjust it with AirfoilPrep to account for 3D effects.
Finally compare with the provided reference data.


Hi xiao,
To generate airfoil data ,using Xflr5 i have designed a foil and flap angle as 1,2,3,4,5 degrees. Using the XY coordinates , i have substituted in airfoilprep.But there no much change in the output CL and CD values.please brief the steps to generate the airfoil data using these two softwares. For what the Xflr5 is used and for what the airfoilprep is used??? Kindly explain the steps!!

Hello Srinvasa,

For the XFLR5, you design the airfoil with flap by defining the profile coordinates. Then you perform a XFOIL direct analysis by changing the angle of attack, you will get a series of aerodynamic coefficients, which are purely 2D.
Here is an example for XFLR5 analysis:

For airfoilprep, it is a correction for 3D effects. The initially aerodynamic coefficients should be obtained from XFLR5. After you get the coefficient, you paste them into airfoilprep, do the interpolate for the angle of attack, correction for the 3D effects, etc. The first README file explains the procedure.

hi Xioa sir;
Everything is ok sir. But where to get the XY coordinates of the blades used in the NREL wind turbine and also how to check the flap action(ie) the airfoil switching in FAST-MATLAB interface. I have designed the airfoil for different flap angles -5 to 5 degrees,

Dear Srinivasa,

Regarding the airfoil geometry of the NREL 5-MW baseline turbine, please see my post dated Jun 04, 2012 in the following forum topic:

Best regards,

Hello Srinvasa,

I suppose you are designing a feedback control scheme.
In order to check the flap angle, what I did is to add a scope module before I feed the flap angle signal back to the FAST module .
(To find it, you can search scope in Simulink library).


Hi xiao,
I am asking about the impact of the flap angle input in FAST outputs!!not while inputting the flap angle??? is there any way to display the switching of airfoil data based on the flap deflection outside ???

You can export the aerodyn data of the blade-flap section.
In aerodyn input file, switch NOPRINT to PRINT.

thank you xiao;
sir i have another query that , i have chosen number of foil as 10 If i try to use flap at 70% of radius of the blade then is it enough to use the xfoil designed data for last 3 airfoil file ?? i have attached the aerodyn input file with the data you have sent with flap -5,0 and 5 degree. is my ideology is correct???
xiao.txt (9.18 KB)
Test001_AD.txt (2.55 KB)

Hello everyone
I did the changes to source code and follow the instructions, Dr.Xiao Sun presented. but the flap angle input signal doesn’t work apparently.
I doubt that doing the compiling instruction correctly, so I write the steps I did.
I used “open project” in “Intel parallel studio XE 2013 with vs2010” compiler and open “Simulink\VisualStudio, FAST_Library.vfproj” file. then I debugged that file without any errors and with 28 warnings.
after that I do the rest of instructions, such as altering “s_function parameters”.
if I did not compile correctly, Let me know.
Thank you

Dear Srinivasa.Sudharsan,
I want to ask you how to solve the problem mentioned above. I’ve met the same question,Could you help me,thanks!

Dear Majid.Ebr,
Could you help me how you solevd the problem later,thank you!

Hello Bonnie,
Currently I am trying to implement trailing edge flaps in FAST v8.16. I am planning on using the MulTabloc function. I have gone through the above mentioned post. I have gone through the FAST_Subs.f90 as you mentioned, but I am unable to find the Multabloc function in this version of FAST. Can you tell me whether its been removed from this version or I have to look for it somewhere else.

Dear Kenneth Paul,

In FAST v8.16, MulTabLoc is a module-level input to AeroDyn v14. To use this feature, you’d have to modify the source code to set the value of MulTabLoc. There is a placeholder at the bottom of SUBROUTINE FAST_Solver.f90/AD14_InputSolve_NoIfW().

Best regards,

Thank you Jason for the quick reply.

Dear Jason,

I have implemented all the necessary changes mentioned in this post to incorporate Flaps, and recompiled the fast Library. but while trying to run with multiple airfoil Tables it shows the error "Error reading multiple airfoil table option. Only one table for each file will be

Upon debugging I found this warning to be generated from AeroSubs.f90. From my understanding the software is not able to read some MultTabLoc identifier in the aerodyn14 input file.

I have attached the aerodyn14 input file as well as the airfoil with multiple tables below. Can you suggest any solution for the problem?

I am using FASTv8.16, with Aerodyn14 and Elastodyn

Note: i am not using Cm values therefore have used dummy values

NACA64_A17_trialFLAP.txt (3.06 KB)
NRELOffshrBsline5MW_Onshore_AeroDyn2.txt (3.53 KB)

Dear Kenneth,

Unless you’ve changed the source code to accommodate this change, I believe you’ve placed “USER” in the wrong place in your AeroDyn v14 input file. “USER” should appear in the line after the table, not in a separate column of the table after PrnElm. The one setting of “USER” applies to all aerodynamic nodes.

Please note that functionality equivalent to MulTabLoc for modeling user-controlled airfoil data, e.g. for flaps and other flow-control devices, is a standard feature of the current version of OpenFAST / AeroDyn. I would suggest upgrading.

Best regards,