Computational study of the Froude number effects on the flow around a rowing blade (original) (raw)
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Numerical modelling of rowing blade hydrodynamics
Sports Engineering, 2009
The highly unsteady flow around a rowing blade in motion is examined using a three-dimensional computational fluid dynamics (CFD) model which accounts for the interaction of the blade with the free surface of the water. The model is validated using previous experimental results for quarter-scale blades held stationary near the surface in a water flume. Steady-state drag and lift coefficients from the quarter-scale blade flume simulation are compared to those from a simulation of the more realistic case of a full-scale blade in open water. The model is then modified to accommodate blade motion by simulating the unsteady motion of the rowing shell moving through the water, and the sweep of the oar blade with respect to the shell. Qualitatively, the motion of the free surface around the blade during a stroke shows a realistic agreement with the actual deformation encountered during rowing. Drag and lift coefficients calculated for the blade during a stroke show that the transient hydrodynamic behaviour of the blade in motion differs substantially from the stationary case.
Fluid Mechanics in Rowing: The Case of the Flow Around the Blades
Procedia Engineering, 2014
The aim of this research is to develop hydrodynamic models to enhance the knowledge of the propulsion efficiency in rowing. The flow around a rowing blade is a complex phenomenon characterised by an unsteady 3D behaviour, with violent free surface deformation including breakup and with a flexible shaft driven by a 6-DOF movement. The study uses experimental results obtained on an instrumented boat to perform CFD computations. All parameters are considered except the minor role played by the spin rotation of the shaft. The numerical results fit fairly well with experimental data given a high number of uncertainties. Once CFD computations fully validated, more accurate parametric models could be built and integrated in a rowing simulator which will help coaching staff in analysing and improving performance and training of athletes. Another considered possibility is the direct coupling between the rowing simulator and the CFD code.
The direction of the water force on a rowing blade and its effect on efficiency
Introduction. 2. Direction of the blade force. 3. Steady flow, model tests. 4. Blade and airfoil compared. 5. Outward tangential force component. 6. Blade velocity relative to water. 7. Efficiency. 8. Typical kinematic values near catch and square-off. 9. Oar bending. 10. Possible hydrodynamic effect. 11. Conclusion.
We consider some scale model experiments in which the forces on rowing blades were measured [Caplan and Gardner, J. Sport Sciences, 25(6), 653-650, 2007]. The experiments were conducted in a flume at a single flow velocity which corresponded to a Froude number, based on the depth dimension of the blade, very close to the critical value of unity. For real rowing, the blade moves at speeds corresponding to Froude numbers in the range of approximately 0.3 to 3.5. We use a computational fluid dynamics (CFD) analysis to investigate the Froude and Reynolds number effects on the forces on a flat plate 'blade', as well as the effects of the flume size relative to the model size in the experiments. We consider only one orientation of the plate to the flow velocity and we consider only idealized steady flow. We find that the flume in the experiments was probably too shallow, so that the measured force coefficients could be 6% higher than for rowing in deep water. Using a series of calculations for fluids with different densities, we show that the force coefficient is independent of the Reynolds number for the range of Reynolds numbers characteristic of real rowing, but is a strong function of the Froude number. There is a sudden decrease of some 30% in the force coefficient as the Froude number changes from sub-critical (less than 1) to super-critical (greater than 1). For Froude numbers greater than 2 the force coefficient increases steadily with Froude number.
Procedia Engineering, 2010
A hydrodynamics-based model of the highly complex flow around a rowing oar blade during a rowing stroke, consisting of an analytical shell velocity model fully coupled with a computational fluid dynamics (CFD) model, is presented. A temporal examination of the resulting blade force for a standard blade, decomposed into propulsive, drag, and lift components, illustrates the flow mechanisms responsible for shell propulsion and a blade propulsive efficiency term is defined. A comparison of blades with modified cant angles reveals that a-3° cant blade has a higher efficiency than the standard (-6° cant) blade.
Sprint Canoe Blade Hydrodynamics - Modeling and On-water Measurement
Procedia Engineering, 2016
A computational fluid dynamics model of the transient flow around a sprint canoe blade has been developed including the full blade motion in the catch and draw phases of the stroke, with the translational and rotational path of the blade is obtained from video analysis of a national team athlete. Examination of the blade path and associated flow patterns around the blade reveals the development of tip and side vortices and their interaction with the blade. An interval of reversed flow and pressure at the top of the blade late in the catch is seen and results in a braking pressure field on the blade surface. On-water measurements have also been made using a new instrumented paddle with multiple strain gauge full bridges. This level of bending moment measurement then allows the tracking of the real centre of pressure of the blade force and the determination of the real blade force (and its components) through the stroke.
Fluid-Structure Interaction and High-Performance Computing to serve sport performance in rowing
2019
With the tremendous growth of computational power, the use of numerical simulations to help analysing and improving sport performance becomes achievable but is still challenging because the physical configurations generally involved coupled problems and because a human is part of the system. Futher-more, elite athletes already operate near an optimal point. As a consequence, the modelization of all the phenomena that come into play has to be accurate enough to be useful and relevant when the objective is to analyse interactions and to give reliable trends while varying some parameters. The case of rowing is presented here, through the development of a high-fidelity simulator of the global system "boat-oars-rower(s)" coupled with the resolution of the Navier-Stokes equations to provide fluid forces acting on it. For this nautical sport, the complexity comes from the non-classical naval hydrodynamics flows around the hull and the blades and from the fluid-structure interacti...
PIV applied to a moving rowing blade
2019
We investigate the fluid motion generated by a moving rowing blade. The blade follows a complex path with rather strong acceleration and subsequent deceleration. The blade path is mimicked at a 1:2 scale in a large open-top water tank using a robot system. The tank is transparent, thus enabling full optical access for performing large-field particle image velocimetry (PIV). The robot system allows us to precisely repeat subsequent rowing blade motions. PIV measurements in the same plane show that the fluid motion is highly repeatable, except for the small-scale turbulent fluid motions. When combined with direct measurements of the forces on the rowing blade (Grift et al. 2019a) the PIV data provide insight in the variation of the hydrodynamic forces acting on the blade during motion. This makes it possible to improve the efficiency and effectiveness of the propulsion which is of great relevance to competitive rowing.
Drag and Power-loss in Rowing Due to Velocity Fluctuations
Procedia Engineering, 2016
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 P V 1 in relation to the total powerP d , as a function of the velocity amplitude A. It was demonstrated that an increase of the velocity fluctuations results in a tremendous decrease of the velocity efficiency e V. The velocity efficiency e V for a typical rowing velocity amplitude A 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 s " 4.7ˆ10 4 , 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 (A ą 20%). From these results, it is concluded that the friction coefficient C f will vary within one cycle. Higher acceleration/deceleration leads to a additional level of turbulent kinetic energy.
A stroke-analysis system based on a CFD (Computational Fluid Dynamics) simulation has been developed to evaluate the hydrodynamic forces acting on a swimmer’s hand. Using the present stroke-analysis system, a stroke technique of top swimmers can be recognized with regard to the hydrodynamic forces. The developed analysis system takes into account the effect of a transient stroke motion including acceleration and a curved stroke path without using assumptions such as a quasi-static approach. An unsteady Navier-Stokes solver based on an unstructured grid method is employed as the CFD method to calculate a viscous flow around a swimmer’s hand which can cope with the complicated geometry of hands. The CFD method is validated by comparison with experiments in steady-state and transient conditions. Following the validations, a stroke-analysis system is proposed, in which a hand moves in accordance with a stroke path measured by synchronized video cameras, and the fluid forces acting on the hand are computed with the CFD method. As a demonstration of the stroke-analysis system, two world class swimmers’ strokes in a race of 200 m freestyle are analyzed. The hydrodynamic forces acting on the hands of the top swimmers are computed, and the comparison of two swimmers shows that the stroke of the faster swimmer, who advanced at 1.84 m/s during the stroke-analysis, generated larger thrust with higher thrust efficiency than that of the slower swimmer, who advanced at 1.75 m/s. The applicability of the present stroke analysis system has been proved through this analysis.