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13:30   Rowing & kayak; hydrodynamics Chair: John Hart 13:30 20 mins TOWARD OPTIMIZATION USING UNSTEADY CFD SIMULATION AROUND KAYAK HULL Alban Leroyer, Régis Duvigneau, Patrick Queutey Abstract: Fluid mechanics is a scientific field that plays a key role in nautical sports, mostly in complex situations. Due to the growing power of computational resources and the development of advanced numerical method, Computational Fluid Dynamics (CFD) becomes more and more popular and is now daily used for applications in naval hydrodynamics (design, prediction of performance,...). The goal of this research work is to apply such advanced numerical techniques to K1 kayak hull, with imposed loads corresponding to those applied by the kayaker onto its boat, to investigate the influence of some parameters and coupled the whole numerical chain with advanced optimization procedure. From on-site measurements with a French elite competitor with sensors daily used in French team, a procedure has been applied to build an analytic and periodic 6 DOF simplified but realistic kinematics. Using this kinematics, unsteady CFD simulations using a Reynolds-Averaged Navier-Stokes solver are carried out by imposing the whole kinematics except the average heave which is computed on-line to balance the weight of the system (hull+athlete). Fluid loads can be thus extracted from the simulation, and the inertia terms can be extracted from the imposed kinematics. As a consequence, by applying the Newton's law to the system “hull”, loads applied by the kayaker onto its boat can be computed numerically. An analytical form of these loads is then deduced through a Fourier transform. Then, these data are used to run CFD simulation by imposing these loads which mimics the action of the athlete, and letting the hull free to move. Once the numerical model is set up, one can investigate the impact of some parameters (longitudinal position of the athlete, hull shape modification, ...) on the performance, keeping the action of the athlete unchanged. The full optimization of these parameters is finally targeted, on the basis of a statistical learning optimization strategy. 13:50 20 mins SPRINT CANOE BLADE HYDRODYNAMICS - MODELING AND ON-WATER MEASUREMENT Dana Morgoch, Cameron Galipeau, Stephen Tullis Abstract: In sprint canoe, the athlete's power is transferred into boatspeed by the blade interaction with the water, a coupling of the hydrodynamics of the flow around the blade and the blade path/motion, which is itself a combination of athlete technique and their response to the blade loads. Here, the motion of a sprint canoe blade through the water is extrapolated from video frame capture of the paddle handle motion of two national team athletes. Computational fluid dynamics is used to model the highly unsteady flow around the blade during the catch and draw phases of single reference stroke (blade path) obtained from the video analysis. Complexities in the simulations include the motion and rotation of the blade and its surrounding grid through the stroke, and in modeling the water surface and blade penetration. The need to account for the bending of the paddle shaft was also seen. The model results provide details of the water pressure patterns on the blade and how the athlete's force connects to the water, and quantitatively how forward and aft blade slip are a result of the flow around the blade. The results include features such as identification of a high inefficiency interval late in the catch phase of the stroke. At this point, an increase in the blade rotation rate causes high pressures on the top of the forward face of the blade - causing a decrease in the forward thrust while still requiring high athlete force application to meet the resultant blade torque. The computational results are also compared with measured force results. A Braca paddle has been in-house instrumented with three pairs of strain gauges, allowing not just shaft bend (proportional to athlete power) but also the location of the blade pressure force to be measured. Decomposition of the blade force into the useful forward and lift components requires simultaneous measurement of the blade orientation, here done using a 6 DOF accelerometer gyrometer inertial measurement unit. Testing of the instrumented paddle was undertaken with one of the authors, an ex-national team athlete (Morgoch). 14:10 20 mins DRAG AND POWER-LOSS IN ROWING DUE TO VELOCITY FLUCTUATIONS Arnoud Greidanus, Rene Delfos, Jerry Westerweel Abstract: The flow motions in the turbulent boundary layer between water and a rowing boat initiate a turbulent skin friction. Reducing this skin friction results in better rowing performances. A Taylor-Couette (TC) facility was used to verify the power losses due to velocity fluctuations in relation to the total power as a function of the velocity amplitude. It was demonstrated that an increase of the velocity fluctuations results in a tremendous decrease of the velocity efficiency. The velocity efficiency eV for a typical rowing velocity amplitude of 20-25% was about 0.92-0.95. Suppressing boat velocity fluctuations with 60% will increase boat speed with 1.6%. Riblet surfaces were applied on the inner and outer cylinder wall to indicate the drag reducing ability of such surfaces. The results of the measurements at constant velocity are identical as the results reported earlier, while the experimental configuration was different. This confirms once more the consistency of the TC-system for drag studies. The maximum drag reduction DR was 3.4% at a Reynolds number Re=47000, which corresponds to a shear velocity in this TC-system with water of V=4.7 m/s. For typical rowing velocity fluctuations, the riblets maintain to reduce the drag with 2.8% and corresponds to a averaged velocity increase of 0.9%. The drag reducing ability of riblets is partly lost due to velocity fluctuations with high amplitudes (>20%). From these results, it is concluded that the friction coefficient will vary within one cycle. Higher acceleration/deceleration leads to an additional level of turbulent kinetic energy.