The Java Virtual Wind Tunnel

A Two Dimensional Computational Fluid Dynamics Simulation

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To understand why airplanes fly, you have to understand fluid mechanics.

But it turns out that fluid mechanics is a tough class to teach. Part of it involves teaching people to solve large and complex systems of equations. That's hard enough in itself. The other part involves teaching them what the answers mean. After all, it's one thing to produce numbers, another thing entirely to visualize the flow of air over a wing and really understand what it's doing.

Unfortunately, teaching students to understand fluid mechanics is very difficult. There's only so much one can draw on a chalkboard (it's very difficult to overlay plots, let alone "animate" a flow). What teachers need is a "wind tunnel" for every student; one they can play around with and do their own experiments.

Well, real wind tunnels are too expensive to give out, but a computer is the next best thing. The Java Virtual Wind Tunnel is an applet which uses computational fluid dynamics (CFD) methods to simulate the flow of air over a two dimensional object. The applet is not just a movie projector; it actually solves the equations of motion (the Euler equations) in real time. So the results on the screen are the real thing, not an animation. And in a virtual wind tunnel, adding instruments costs nothing. In fact, the simulation provides more information about the flow than you could easily access in any real wind tunnel.

The Java Virtual Wind Tunnel is just a prototype. But it shows how Java can be used to build educational tools for undergraduate and graduate fluids mechanics courses. At the undergraduate level, the simulations might help students visualize and understand 2-D fluid flow. At the graduate level, it might help students understand the power and limitations of computational fluid dynamics.

The prototype Java Virtual Wind Tunnel is running at the top of this page. This demonstration shows the flow of air through a channel with a "bump" in one of the walls. If you let the applet run, a shock wave will appear above the bump where the flow jumps from supersonic to subsonic speeds. Moving the sliders will change the flow conditions and cause the shock to appear and disappear.

To learn more, try one of the following pages.


Thanks to Bob Haimes ( for helping me with the Visualization algorithms.

Matthew Gray ( for his help with the animation.

Professor Kenneth Breuer ( for teaching me Computational Fluid Dynamics.

And many thanks to the people at the MIT SIPB.

And in your spare time, feel free to check out my homepage as well.

If you would like a copy of the source code for this applet, send me email at Don't worry, I don't bite.

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Last modified: September 2001

David Oh / Computational Aerospace Sciences Laboratory, MIT /