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14:40   Aerodynamics; drag reduction Chair: Timothy Crouch 14:40 20 mins THE USE OF VORTEX GENERATORS TO REDUCE THE AERODYNAMIC DRAG OF ATHLETIC APPAREL Len Brownlie Abstract: In world class athletic competitions the margin of victory is often exceedingly small and in a range that maybe influenced by aerodynamic drag (Fd). Vortex generators (VG) are small triangular or vane shaped protuberances that have been used successfully in automotive and aerospace applications to stir the boundary layer and delay flow separation over a wing or body surface. To determine if VG would reduce the Fd of a sprinter or marathon runner, a series of Fd measurements were conducted on circular cylinders, mannequin limb segments and full-scale mannequins in wind tunnels at the University of British Columbia and University of Washington. A large variety of VG shapes, sizes and patterns were developed using computer-aided design and rapid prototype printers. In total, the test program involved 1,540 discrete multi-velocity test runs requiring 56 days of wind tunnel time. The test program successfully identified specific arrangements of VG that, in combination with well-fitted garments, would reduce the Fd associated with running apparel by up to 9.8%. Specific body maps based on race distance and gender were created to optimize the application of VG to different types of running apparel. Unlike previous apparel based drag reduction strategies that utilized multiple textured fabrics to reduce Fd, the VG based Fd reduction strategy provided three key advantages: (i) it became effective at a very low velocity and so can be used on apparel designed for either higher velocity (sprint) or lower velocity (marathon) running activities; (ii) it did not undergo a post-flow transition increase in Fd; and (iii) only a few rows of VG were normally required so that the weight and complexity of manufacturing the apparel were reduced. Mathematical modeling of sprint, middle distance and marathon performances at a world-class level suggest that aerodynamic apparel with VG could provide time savings of 0.018 seconds in 100 m, 0.61 seconds in 1500 m and 14.7 seconds in the marathon for male athletes wearing apparel with VG versus those wearing competitor 2012 Olympic apparel without VG. The results of this study suggest that appropriately sizes and patterns of VG can provide a significant reduction in the Fd provided by running apparel. 15:00 20 mins ANALYSIS OF AERODYNAMIC DRAG FROM PIV DATA IN SPEED SPORTS Wouter Terra, Andrea Sciacchitano, Fulvio Scarano Abstract: Aerodynamics plays a crucial role in many speed sports. The aerodynamic drag is often the main force the athlete has to overcome reaching 80% of the total resistance in speed skating, and up to 90% for road cycling [1]. A small reduction of the aerodynamic drag can mark the difference between winning and losing a competition. Aiming at the aerodynamic drag reduction, different studies [2,3] remark that it is crucial to obtain a better understanding of the dynamics of the entire flow evolving around the athlete that lead to the aerodynamic loads. A point, not often noted, is the effect of off-site testing of athlete aerodynamics in wind tunnels. Off-site testing provides accurate results if the experiment is carefully conditioned. This, however, can be complicated due to the need of artificial structures (e.g. a support to hold a mannequin, moving floor system) to conduct the experiment. In that sense, on-site tests are preferred. However, to date, on-site aerodynamic tests only allow the estimation of the resulting drag force acting on the athlete. A system for on-site quantitative airflow visualization is missing. Tomo-PIV is an experimental technique that allows measuring the flow velocity in a three-dimensional region [4]. Small particles are added to the flow medium. The particles are illuminated by a light source, typically a laser or LED system, and imaged by digital cameras. The velocity in the imaged region is obtained from the particle image displacement. We propose to use this technique for on-site sport aerodynamic investigation via the ring-of-fire concept: the measurement system is integrated in a “tunnel”, through which the athlete passes during the training. The objective of this study is to prove the feasibility of the ring-of-fire concept on a scaled version of the system. Figure 1 shows the scaled ring-of-fire (50×50 cm2 test section) that has been developed. This system was used to carry out a quantitative visualization of the three-dimensional flow field over spheroids of different shape (sphere and conical aft) and size (8 and 16 cm diameter) moving at about 1 m/s. The system successfully measured the main characteristics of the airflow over the spheroids. The full paper will present a quantitative comparison with the velocity fields reported in literature to assess the accuracy of the ring-of-fire concept. Furthermore, the aerodynamic drag of the spheroids will be evaluated from the measured velocity fields. References 1. G. Gibertini and D. Grassi, Cycling Aerodynamics, in Sport Aerodynamics, Helge Nørstrud Editor (2008) 2. R.A. Lukes, S.B. Chin, S.J. Haake, The understanding and development of cycling aerodynamics, Sports Engineering 8, 59-74, ISEA (2005) 3. T.N. Crouch, D. Burton, N.A.T. Brown, M.C. Thompson, J. Sheridan, Flow topology in the wake of a cyclist and its effect on aerodynamic drag, Journal of Fluid Mechanics, 748, 5-35 (2014) 4. F. Scarano, Tomographic PIV: principles and practice, Meas. Sci. Technol. 24 (2013) 15:20 20 mins DRAG REDUCTION BY APPLYING SPEEDSTRIPS ON ROWING OARS Conno Kuyt, Arnoud Greidanus, Jerry Westerweel Abstract: Dutch speed-skaters used a zig-zag strip on their head during the Nagano Winter Olympics 1998 to reduce air-resistance and won 11 medals (5 Gold). Since 2000 these ‘speedstrips’ are also used to reduce the air-resistance of rowing oars, even though this air-resistance is very marginal compared to the total resistance that a rowing boat encounters during the forward motion. The objective of this study is to determine the advantage of the application of zig-zag strips to rowing oars for a lightweight single sculler. The research method comprehends three steps; (1) the analysis of the rowing oar movement, (2) the determination of the change in drag coefficients and (3) the composition of a rowing model. Parameters that are important to analyse the rowing oar movement are boat velocity and oar angle as a function of time and the oar geometry. The change in drag coefficients due to zig-zag strips was determined by wind tunnel experiments. Cylindrical-shaped objects with different diameters were placed in an open wind tunnel facility. The total force on the cylinder was measured with load cells for a range of wind velocities (2-20 m/s). The software program MATLAB-Simulink was used to compose the rowing model. The new drag coefficients identified by the wind tunnel experiments were used to determine the final advantage of the application of zig-zag strips to rowing oars. The speedstrips induce a 0.1% advantage over a 2000m race for calm wind conditions. The advantage increases to 0.4% when the headwind velocity is 5 m/s. For bigger boats, the advantage might be even larger.