Spherical bubbles tend to rise in pairs, if one bubble is behind, following in the wake of another, it gets speeded up in the upward-moving wake, catches up, hits the top bubble, they tumble, and then both travel in horizontal alignment.

However, the shape of the bubble is dependent on the surface tension of the fluid.

"But as the surface tension drops and the bubbles flatten, this forces the flow to go around in a different way. The ellipsoidal bubbles become little winglets, and that changes the direction of the lift, completely reversing it so that it draws them into the faster moving fluid found in the wakes of passing bubbles. As a result, unlike spherical bubbles, flattened bubbles will sometimes stream together, following each other up in narrow columns,"

In the future, the researchers hope to extend the model to include phase change and mass transfer as well as modeling fundamentally different bubble behavior, for example large single bubbles which can wobble and follow a spiraling pattern as they ascend.

A few of the enhancements in the new version include:

• Interactive Command History Window
• Diagnostic Tools
• Double Precision
• New Elliptic Smoothing Techniques
• Interactive Spotwelds
• More Support for CAD

The Immersive Boundary (IB) Method attempts to model the elastic material as a part of the fluid with additional forces due to elastic stress. The fluid equations are solved in a Lagrangian fashion on a fixed regular lattice mesh. The elastic material is tracked by following a collection of representative points as they move across the mesh. The spacial configuration of these points is used to compute elastic forces which are applied to nearby fluid points in the lattice. In general, the method is applicable to any problem in which a fluid interacts with a flexible material.

The IB method has been applied to a wide variety of problems including a beating three-dimensional heart, valve-less pumping, blood clotting, the swimming motion of fish and eels, and the inner ear.

In such problems, the immersed boundary method opens up the prospect of raw simulation, almost akin to experiment, in which something approaching the full complexity of the system is allowed to operate in the model. -- Charles S. Peskin and David M. McQueen

www.airflow.ethz.ch
www.afc.ch
www.cfx-germany.com"

These calculations have allowed the capture efficiency of the local exhaust system to be estimated within the real working environment. Based on these results a prototype has been built and is now undergoing final testing in the wind tunnel. CFX-5 has proved to be a useful tool with which to optimise the REEXS design and will be used in further research for dimensioning of specific REEXS systems."

The RAVE (Reconfigurable Advanced Visualization Environment) consists of 3 8 foot by 8 foot rear-projection screens which can be configured as an 8x24 wall, or as a three-wall immersive environment.

"With EnSight Gold on the RAVE, a detailed model of an intricate structure with many components, such as a jet engine, can be viewed from all angles and diverse vantage points," says Jay Horowitz, visualization manager at NASA Glenn. "We can now bring our data visualizations more 'out of the screen' than before. It is surprising how much better you can understand complex phenomena when you have more control over how you view it."