Interference under the water – part 1
Mikko Brummer All simulations
by
performed by
WB-Sails with XFlow, from Dassault Systémes
© WB-Sails
I
n a previous article, we looked at the interference between boats above the sea, in the air – backwinding, bad air and so on. Boats interact with each other under the water, too. This interference is slightly different, though. While the air is moving (wind), and the boats are moving within it, the sea is inert unless there’s current or tide. The bad air 18
FINNFARE APRIL 2019
from the sails is spread along with the wind, affecting larger areas behind the boat, while the disturbance by the boat slicing through the water mainly remains in its wake. Some of the disturbance is spread along the water as waves, and on the other hand, the disturbances (vortices and swirls) remain active in the water much, much longer than in the air, due to a difference in viscosity of these two phases. When tank testing models, one has to wait 10-15 minutes for the water to calm down between test runs, else the results will be meaningless. In the wind tunnel, waiting times are much shorter, as vorticity dissipates in the air much more rapidly.
