Twist Flow Wind Tunnel
General Purpose of the Wind Tunnel
YRU-Kiel has built a Twisted Flow Wind Tunnel (TFWT) for the investigation of sails for contemporary sailing yacht design. The TFWT mimics the shear flow a yacht encounters when sailing in natural wind boundary layer. It's primary purpose is being an investigation tool for the optimization of the shape of upwind and downwind sails.
The TFWT features adjustable shear flow of up to 10 m/s flow velocity, a model size of 1.8 m mast span, a highly accurate 6 DOF force balance and a photogrammetry equipment for the evaluation of the flying shape of the sails.
Yacht Model and Trimming Devices
The yacht model, which is fixed to the measurement table, consists of a base frame and a hull/deck model. The rig has a modular set up. The main dimensions of the rig (J, I, E, …) as well as the number of stays, spreaders and supports can be changed with minimal effort. The stepper servos of the winches are controlled by the measurement PC with the help of virtual instruments and control levers.
Shape Measurements and Photogrammetry
The wind tunnel is equipped with sail shape measurement techniques based on photogrammetry. The actual flying shape of the sail under optimum trim condition can be acquired simultaneously with flow force measurements.
Coded Targets / NURBS surface generated from Coded Targets
Velocity, Twist Angle and Turbulence Intensity Profiles or the evaluation of flow velocity profiles in the measurement plane a 3D Dantec CTA is used. The CTA allows to measure the flow velocity profile in three dimensions.
Contour plot of the impact of the twist vanes on the flow profil
Typical Results and VPP processing
In the context of the speed prognosis (in-house VPP) the wind tunnel driving and side force coefficients are converted into lift and drag coefficients to be integrated in our AVPP velocity prediction program. The velocity polar diagram is the ultimate measure for the merit of a sail design. It allows to compare different sail designs and provides valuable data for the handling of the sail, namely cross-over wind angles and wind speeds for sail changes.