Company uses 3D air flow simulation

Fredrik Lööf & Anders Ekström are Swedish medal hopefuls in the Star class in Beijing. This 3D air flow analysis using EFD.Lab reveals massive flow separation behind the Star jib sail at angles near stall.

Finland-based sail maker WB-Sails is using EFD.Lab fluid dynamics simulation software from Flomerics to develop and optimize sails for Star and Finn class Olympic sailboats.

“Our traditional panel codes predict sail forces reasonably well in the upwind case, when flow separation is not a major factor, but we were desperate for something more powerful to predict 3D air flow and sail forces on downwind legs and in the lighter winds that we expect in Beijing,” says Mikko Brummer, Head of R&D at WB-Sails.

“We had been looking for some time at traditional Computational Fluid Dynamics (CFD) software programs but we found them too slow and cumbersome for our purposes," says Brummer.

"In EFD.Lab we found exactly what we were looking for - an extraordinary ease of use provided by features such as “direct CAD-to-CFD” technology and automatic mesh generation. This gives us the very fast turn-around times we need for looking at alternative “what if?” design scenarios. The detailed predictions coming from EFD.Lab have made us aware of 3D air flow phenomena that we never knew existed," he continues. "Another thing we have learned is that the mast, which is usually considered as a necessary device that adds drag, can actually add to the driving force of the boat.”

WB-Sails uses EFD.Lab to pinpoint problem areas in sails where flow separation is likely to occur. Flow separation reduces the driving force in the sail and increases drag. Simple sail trim changes can be performed directly within the software, and the close coupling with CAD software makes it easy to change components such as sails and rigging.

For regions of particular interest a denser local mesh can be created quickly making it possible to investigate detailed flow phenomena in a reasonable time with an ordinary desktop PC.

The EFD.Lab CFD software allows non-uniform air flow conditions to be specified at the entry plane to represent the atmospheric boundary layer at the sea’s surface. When combined with the speed of the boat this results in a complex "sheared" and "twisted" wind pattern approaching the sails. The built-in graphical post-processor in EFD.Lab enables air flow trajectories and pressure forces to be visualized with full 3D animation, making it much easier to understand the results.

Driving force, heeling force & turning moments are calculated and output in absolute and coefficient form. These forces are used to predict and optimize the sailboat's performance. “We hope this will lead to medals for our sailors in the Star and Finn class at the Beijing Olympics in August 2008,” says Brummer.

For more information about EFD.Lab, visit click here