| Themes > Science > Physics > Fluid Dynamics > Flying the flag for fluid dynamics > Aerodynamics > Selected Topics of Model Aerodynamics > Designing an Airfoil > The Drela Code «XFOIL» |
This code also includes design as well as analysis tools, which have been combined very comfortably, with ease of use in mind. The code is intended as an interactive application, but because it does not directly make use of a proprietary window system, it is quite portable and can be used in batch mode by input redirection. The design module of the FORTRAN 77 code has to be used as a redesign method, i.e. you need a starting geometry, whose velocity distribution can be modified, and you have to be very careful to avoid waves and wiggles when adding changes to the leading edge region. It is practically impossible to design the leading edge region as smooth as with Eppler's method. The analysis module consists of a 2nd order panel method (linear varying velocity), which cannot achieve the accuracy of Eppler's panel module. But in contrast to Eppler's simple boundary layer method Drela has implemented a more sophisticated method, which takes the boundary layer into account while solving for the flow field. Thus the interaction between boundary layer and external flow is modeled quite realistic and the code can also handle small to medium sized separated regions. When the separation is getting larger or extends into the wake, the results are getting worse, but usually are still acceptable for an impression of the airfoil behavior. The transition prediction, which is of utmost importance for low Reynolds number airfoils, is based on a so called e^n method, which is used as a simplified envelope method. In some cases, the errors introduced by this envelope method can be quite large though. |
|
|