The Java Virtual Wind Tunnel
Controls and How to Use Them
As you can see above, the Virtual Wind Tunnel consists of a display
window surrounded by different buttons and sliders. These buttons can
be used to change the simulation and/or change the information
displayed in the window. The best way to learn the controls is
to play with them, but here are some hints to help you figure them
out. All the control described here may not appear in your
window depending on the size selected for the applet's width and
height (i.e. controls will be sacrified in order to make everything
fit on the screen).
A brief note here about the use of sliders: a slider's value can be
changed either by clicking on the scroll bar or by typing a value in
the slider's display window.
- The two boxes in the upper left corner of the window let you
choose between contour plots and line plots of various
flow parameters (Density, Mach Number, etc). Contour
plots are 2-D color plots of the flow field. A key is shown at
the right, and the minimum and maximum values change to match the
flow. Line plots are graphs of some quantity vs. distance from
left to right (which I call the "axial" direction). A line plot is
actually three plots in one window which show conditions along the top
wall, the bottom wall, and the center of the grid.
- The pause button pauses the flow (go figure). Technically,
it pauses everything, including plotting functions, so you can
basically "turn off" the applet without leaving this page.
- The grid button allows you to see the computational grid.
Clicking it once turns the grid on, once more turns it off. The grid
is technically referred to as a "structured" mesh. It need not be
square or even uniform (as demonstrated in the example of a supersonic flow).
- The tufts button allows you to turn on simulated tufts of
string that help you see which way the flow is going. Clicking it
once turns the tufts on, once more turns them off. A tuft is placed
at each grid point.
- The local timestep/time accurate box lets you choose
between local timestepping and time accurate simulations. Local time
stepping is the faster method, but is not as realistic as a time
accurate simulation. For more details, see the technical discussion.
- At the bottom left of the screen is a slider that controls the
inlet mach number The mach number is the ratio of the flow
velocity to the speed of sound. Manipulating this slider changes the
speed of the incoming flow. This is the heart of the applet; using
the slider, you can make shocks appear and disappear and see how it
changes the pressure and temperature distributions, etc. For
stability reasons, the slider will cover either a subsonic range (from
mach 0.3 to mach 0.9) or a supersonic range (from mach 1.3 to 2.5)
depending on the initial conditions.
- The next two sliders control the fourth order and second
order damping coefficients. These coefficients change the amount
of smoothing used in the simulation. A certain amount of smoothing is
necessary to remove numerical instabilities from the solution. By
manipulating these sliders, you can see the effect that larger and
smaller amounts of smoothing have on the flow.
Now that you know how to use the simulation, you can
June 8, 1996
David Y. Oh / Computational Aerospace Sciences Laboratory, MIT / email@example.com