## JavaFoil — Analysis of Airfoils |

JavaFoil is a new implementation of my
older CalcFoil program. Like SimProp, CalcFoil
was written solely for my web pages using the "C" language. After rewriting SimProp using the "Java" language, I started to
write JavaFoil for the same reasons (see my
JavaProp pages). |

*JavaFoil* is a relatively simple program, which uses several
traditional methods for airfoil analysis. The following two methods build the
backbone of the program:

- The
__potential flow analysis__is done with a higher order*panel method*(linear varying vorticity distribution). Taking a set of airfoil coordinates, it calculates the local, inviscid flow velocity along the surface of the airfoil for any desired angle of attack. - The
__boundary layer analysis__module steps along the upper and the lower surfaces of the airfoil, starting at the stagnation point. It solves a set of differential equations to find the various boundary layer parameters. It is a so called*integral method*. The equations and criteria for transition and separation are based on the procedures described by Eppler [13, 14, 15].

A standard compressibility correction according to Karman and Tsien has been implemented to take mild Mach number effects into account. As long as the flow stays subsonic (V below V* in the Velocity diagram), the results should be fairly accurate. Usually this means Mach numbers between zero and 0.5. You cannot analyze airfoils in transonic or fully supersonic flow with the methods in JavaFoil.

Some additional tools for creation and modification of airfoils have been added to fill the toolbox.

If supplied with the right food, the computer code will examine your airfoil.
First it will calculate the distribution of
the velocity on the airfoil surface which can be integrated to obtain the lift
and the pitching moment. Then it will calculate the behavior of the flow
close to the airfoil surface (the *boundary layer*). The boundary layer
data can be used to calculate the *friction* drag of the airfoil as well as
the *pressure* drag. Because the drag integration would be rather
inaccurate, the total drag is obtained from the boundary layer parameters at the
trailing edge, using the "Squire-Young" approximation. Both steps (potential
flow and boundary layer analysis) are
repeated for the given range of angle of attacks, which yields a complete polar
of the airfoil for one fixed Reynolds number.

Note that the calculations are performed by a computer code of my own, **not**
by the Eppler or the XFOIL program. Only the
boundary layer module was directly based on
the method which is also found in the initial version of the Eppler
program. Additions include new stall and transition models.

As said above, *JavaFoil* is a relatively simple program, with limitations. As with all engineering computer codes, it is up to the user to
judge and to decide how far he wants to trust a program. Because *JavaFoil*
does not model laminar separation bubbles and turbulent flow separation, the results will
be incorrect if larger areas of flow separation are present. Massive separation, as it occurs at stall,
is modeled to some extent by empirical corrections, so that maximum lift can be
predicted approximately for "conventional" airfoils. If you analyze an airfoil beyond stall,
the results will be quite inaccurate. It is questionable, whether any two
dimensional analysis method can be used at all in this regime, as the flow field
beyond stall is fully three dimensional with spanwise flow and possibly strong
three dimensional vortices.

**Please read all (yes, if I say all, I really do mean all!) the
comments, instructions and tips - this may spare you time and trouble and lead
to more realistic results. You might want to print out some pages for easier
reading. There is also a short
User's Manual in PDF format available.**

*Last modification of this page:
21.05.18*

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Martin Hepperle.**

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