Sail Simulation

The modelling of sails and yachts poses some interesting challenges to CFD.  Two of these are the modelling of the separated flows behind offwind sails and the wind twist that occurs.

As part of TotalSim’s R&D program we investigated both of these issues.

The issue of sail separation is well suited to DES modelling.  This takes CFD beyond the steady state approach commonly used and allows us to see the transient flow structures that develop in the wake of the sails.  The video above shows the modelling of an offwind rig, using IsoSurfaces to show the wake.  The video starts from a RANS solution which is used as the starting point for the DES simulation.  As the simulation continues the highly transient flow structures can be seen.

Typical CFD mesh around yacht deck gear.

All simulations are carried out within the opensource CFD code OpenFOAM® ** and TotalSim’s customised release.

The inclusion of all the deck gear for windage studies is also now easily achievable.  The images right show the level of detail that can now be included within CFD simulations.  If geometry of the equipment exists it can now be included with minimal increase in geometry preparation and simulation time.

Another part of the offwind modelling puzzle is that of modelling the wind twist.  This is caused by the combination of both the atmospheric boundary layer and the boat speed.  TotalSim have now introduced a simple to use list of options to control the twist.  The user enters boat speed, true wind angle and a few other fields and the correct twisted wind profile is applied.  Two variants of atmospheric boundary layer profile have been included and validated against their analytical form.

This is now being used by some of our relevant support customers.  If you would like to know more about how TotalSim can help you with you sail simulation needs, either through consultancy or as a support customer then please contact us.

**OpenFOAM® and OpenCFD® are registered trade marks of ESI.