JavaFoil presents itself in a single window or in a single applet area in your browser. It contains a row of tabs on top and a card area below. Each tab shows its associated card which contains input and output elements for a certain topic.
The cards are divided in topics like Geometry, Modify, Velocity, Flow Field, Boundary Layer, Polars and Options. Most of these cards have a button bar at the bottom, which contains command buttons acting on this specific card. Depending on the security settings of your Java system, some of these buttons may be inactive (see Applet or Application). Each card is described in more detail in the following sections. Some cards have a "Tear Off" button, which pulls the card from the card stack and shows it in a window of its own so that you can access it while working on another card. When you close the card window, it will be put back onto the card stack.
In JavaFoil you work with a single "virtual" working airfoil. This means, that you have one airfoil, which can be designed, analyzed, modified and analyzed again an so forth. All modifications like flap deflection, importing a new blade geometry will alter this virtual airfoil. You might want to save intermediate airfoils.
Usually most data are normalized (e.g. chord length = 1.0). In all other cases, the unit system is metric for input data and results. Some conversion factors for metric and imperial units are given on the Tips and Tricks page.
Language and decimal character:
JavaFoil uses your systems language settings to select the strings used for any textual output as well as to define the decimal character. See the description of the Options Card below.
Printed user's manual:
This page presents a short overview only. You can download a PDF version of a more detailed user's manual.
|The Geometry card is used to prepare the coordinates of your
current airfoil. This is the geometry which is used by all tools in
It shows a list of coordinates and a plot of the resulting airfoil shape. You can enter or paste arbitrary coordinates into this field and press the "Update View" button to copy the coordinates into the working airfoil. Remember that the coordinates must be ordered trailing edge > upper > nose > lower > trailing edge.
Additionally it contains options to create standard airfoils from several families, namely:
Note about all x-y graphs:
|These NACA airfoils are still used in a lot of
applications, but most of them are not top performers by today's standards.
As the original definition creates airfoils with open trailing edges, an
additional option is provided to close to airfoils smoothly.
You can save the generated coordinate set in several file formats. Note that JavaFoil recognizes the file type by its extension, so you have to stick to the proposed extensions.
|Here you find tools to modify the geometry of the current
You can create a new distribution of points, change the camber and the thickness or deflect a plain flap. A scaling and rotating option is also available to transform the airfoil. The result of any modification is shown at the bottom of the card and is also transferred back to the Geometry card. Each transformation is executed when you press the button to the left of the corresponding text entry field.
Before a modification is performed JavaFoil saves a copy of the current geometry on top of a stack and you can either use the "Undo" button to back up to the previous configuration or select the desired configuration from the combo box. It is recommended to enter a name which reflects your modification before pushing the "Modify" button (e.g. "NACA 0010 / F+10" for a 10° flap deflection). To reduce memory overhead, the number of undo steps is currently limited to 10. Each additional modification will drop one saved geometry from the bottom of the stack.
|This card can be used to design an airfoil based on a
prescribed target pressure (coefficient) distribution. Such a method is called "inverse design" -
the geometry of the airfoil is a result of the given pressure
Pressing the "Setup" button initializes the design procedure by copying the current airfoil. This airfoil is then analyzed at the given angle of attack and produces an initial target pressure distribution.
Now you can modify this pressure distribution either by using a smooth distortion of the target Cp or in a single point mode. Simply grab a point on the target distribution and drag it up or down to modify the curve.
After you are satisfied with the target Cp-distribution, you can run several design cycles and check the result. The current solution is overlaid on the previous results to allow for convergence check.
You can "Redraw" the screen to clear the intermediate results.
Instead of viewing the Cp-distribution in the usual way Cp=f(x/c) you can "unfold" the distribution by plotting Cp=f(s). Here s is the arc length measured along the airfoil surface (the order is upper surface, nose, lower surface). This representation makes it easier to modify the leading edge region. When this viewing mode is active, a slider can be used to enlarge the leading edge or trailing edge regions.
A relaxation factor helps to stabilize the procedure and to smooth the geometry changes - usually a value between 10% and 25% is sufficient.
Typically, the number of design steps should be between 10 and 50 steps. You can repeat the design until JavaFoil has reached the target.
The analysis takes into account the effects of ground proximity as well as multiple elements. Note that the design procedure only acts on the first element of multiple elements. You have to change the order on the Geometry card if you want to design another element.
If you want to define the target pressure distribution by numbers, you can use the "Details..." button to open a window where you can enter or paste x/c, y/c, Cp triples. From these data, JavaFoil only reads the Cp values, changing x/c or y/c will have no effect.
|This card can be used to calculate the velocity distribution
on the surface of the airfoil for several angles of attack. As usual, all
angles are counted from the x-axis of the airfoil.
The graph shows the velocity on both sides of the airfoil and can be used to smooth airfoils. If the velocity distributions show wiggles and zig-zag waves, any subsequent boundary layer analysis on the Polars card will probably create unrealistic results. To smooth an airfoil, go back to the Geometry card and change single y-coordinate values or use the Design card to modify the velocity distribution directly. Then re-analyze. Yes, this is slow, but possible and probably better than an automatic global smoother which would smooth over the whole airfoil.
You can display either the distribution of the local velocity v/V or the resulting local pressure coefficient Cp. If a Mach number other than zero is specified on the Options card, the critical velocity ratio V* respectively the critical pressure coefficient Cp* is plotted also. The distributions are corrected for compressibility effects by the Karman-Tsien rule, but one must be aware of the fact that such corrections are valid only for Mach numbers below approximately 0.7.
|If you want to get an impression of how the flow around the
airfoil looks like, this card is for you. The panel analysis method
works with the surface of an airfoil only, but when the surface velocity has
been determined, potential flow theory can be used to calculate the flow
velocity and direction anywhere in space.
You can specify a regular x-y grid and an angle of attack. After solving for the surface velocity distribution, an evaluation is performed for each point on the grid.
The buttons in the control bar at the bottom of the card perform the following actions:
|You can select from the following display
|This card is a source of information for the experts. It
shows all important boundary layer parameters like thickness and shape
functions. Additional parameters are available in the listings. The
abbreviations and symbols can be found on the quick reference card page. A
fixed transition location can be defined on the Polars card (see below).
|When you have created or imported a sufficient smooth
airfoil shape, you can calculate lift and drag on this card.
After specification of the desired Reynolds number and angle of attack range as well as selecting a surface roughness you can start the analysis. For each Reynolds number / angle of attack condition, JavaFoil will first calculate the velocity distribution and then perform a boundary layer analysis. The resulting lift, drag and moment coefficients as well as location of transition and separation will be presented in graphs and tables. A transition strip can be simulated by specifying a transition location x/c for both sides of the airfoil (the default setting of 100% corresponds to natural transition).
The user can select between different stall and transition models (the transition models are described here).
Note: It is not necessary to use the Velocity Card before calculating polars.
|The Polars card analyzes your airfoil for constant Reynolds
numbers. For an aircraft in flight the lift coefficient depends on the
flight speed and hence on the Reynolds number.
The Aircraft card makes it possible to analyze airfoils in an aircraft oriented way. It does not analyze and aircraft, though!
Instead of specifying a Reynolds number range you specify a range of wing loadings. Additionally you define the mean chord length and of course a range for the angle of attack. For each wing loading / angle of attack condition, JavaFoil will now find the matching Reynolds number. Like on the Polars card, the resulting lift, drag and moment coefficients as well as location of transition and separation will be presented in graphs and tables.
Note that the kinematic viscosity and the density are taken from the Options card. For different altuitudes you have to adjust these values accordingly.
|This card offers some information about your Java system and
it contains a combo box to select a different country setting. The
country setting also affects the decimal separator. Initially, the
language will be selected automagically, based on your system settings (or
according to your command line parameters). The default language is English,
but if you prefer your native language, contact me by eMail to receive a
file with the character strings to translate.
You can save and restore the current state of JavaFoil to revert later to a previous project (see security settings).
Also you can specify some properties of the fluid where you want the airfoil to operate. The kinematic viscosity is needed for the calculation of the local Reynolds number and the speed of sound is needed for the Mach number. Currently, these parameters are currently only required for the Aircraft card.
The aspect ratio is used for an approximate correction of the results on the Polar and Aircraft cards for a finite wing. First the 3D lift coefficient CL is determined by adapting the 2D Cl. Mach number and aspect ratio are taken into account. Then the 3D drag coefficient CD is calculated by adding the induced drag coefficient for a wing with elliptical lift distribution to the Cd of the airfoil.
Finally, the scripting facility can be used to automate simple command sequences.
Last modification of this page: 16.02.08
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