Blog

XFOIL Tips - No.1 - Airfoil Import & Reshaping

XFOIL Tips - No.1 - Airfoil Import & Reshaping

The XFOIL module is an integral part of the QBlade interface. It is a powerful and efficient airfoil simulation tool and it is worth mentioning some of its capabilities as well as some useful tips and tricks. 


The XFOIL module includes an integrated airfoil shape generator for various series of the NACA airfoils. You can however download and import any other airfoil shape in the typical XFOIL format. The most common airfoil format that can be handled by the XFOIL module of QBlade are: 

The Plain Coordinate Style

This contains the X and Y coordinates, starting from the trailing edge around the leading edge and back to the trailing edge, staring either from the pressure or the suction side.

EXAMPLE:

X(1)  Y(1)
X(2)  Y(2)
.     .
.     .
X(N)  Y(N)

 

The Labeled Coordinate Style

This is the same as the previous style with the only difference that it includes the airfoil name on the 1st line of the file. This is the most convenient formal since it allows the user to keep a good control of various airfoil files even if a file-name is accidentally renamed. 

NACA 4412
X(1)  Y(1)
X(2)  Y(2)
.     .

.     .

X(N)  Y(N)


After importing or generating an airfoil shape it is necessary to run a series of smoothing and reshaping functions in order to ensure the proper representation of the airfoil and trouble-free simulations.

Generally the airfoil shapes are by default normalized to a chord length of 1 unit length. However the airfoil import module allows the user to import airfoils that are also out of scale. In order to ensure a proper airfoil chord length it is necessary to select the Normalize option. 

The next step is to perform a De-Rotation in order to ensure that the airfoil Leading Edge and Trailing Edge represent the chord extremities. NOTEIf you want to experiment with the integrated leading edge flap and trailing edge flap generator you should NOT de-rotate the generated airfoils in order to allow for easy comparison among various configurations.

The last point of the airfoil import process is the surface smoothing. You can use a Global or Local Refinement and determine the angle between panels as well as the total number of panels. The Global Refinement is usually preferred as well as the standard number of 160 panels. Higher number of panels will only slow down the computation, while lower number of panels might lead to sharper angles between panels. 

When simulating airfoils for large wind turbine blades it is necessary to take into account the proper trailing edge thickness as well! Current blade manufacturing and transportation limitations do not allow knife-sharp trailing edges to be manufactured. For this reason the built-in Trailing Edge Gap function is used in order to generate a blunter trailing edge without truncating the airfoil.

The QBlade Team!