SIMULATINGTHE UNSTEADY HYDRODYNAMICS OF A ROWING OAR BLADE

Abstract

<p>The highly unsteady free surface flow around a rowing oar blade in motion is<br />investigated using modelling techniques. The ability of the numerical model to replicate<br />this complex flow is demonstrated by using computational fluid dynamics (CFD) to<br />simulate previously performed steady-state experiments involving a qum1er-scale rowing blade in a water flume. A comparison of drag and lift coefficients from the experiments and the simulations reveals excellent agreement, providing confidence in the numerical model to handle similar flow conditions. The computational domain is then expanded to simulate a full-scale blade in open water conditions, and steady-state drag and lift coefficients are compared to those previously simulated for a qum1er-scale blade in a flume, revealing substantial differences in magnitude. The computational domain is then modified to allow for oar rotation, as in actual rowing. A force-based rowing model is derived, calculating the instantaneous velocity of a shell based on the propulsive force generated by the motion of the oar blade in the water, the hydrodynamic drag on the shell, and the motion of the rowers within the shell. Using the shell velocity and a prescribed oar angular velocity, the CFD model calculates the highly unsteady blade flow, providing instantaneous drag, lift, and propulsive forces on the blade, in tum driving the rowing model.</p> <p>The dynamic blade-water interaction is depicted in six distinct flow regimes,<br />characterized by the relative motion of the blade in the water and the temporal influence of drag and lift. It is seen that the propulsive force generated by the blade is largely liftinduced through the first half of the stroke. During the middle of the stroke, drag increasingly influences the propulsive force. At end of the stroke, the propulsive force is once again largely lift-induced.</p>