Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E17: Fluid Dynamics in Sports |
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Chair: Barton Smith, Utah State University Room: Georgia World Congress Center B304 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E17.00001: Velocity fields of pitched baseballs using Particle Image Velocimetry Nazmus Sakib, Barton Smith Baseballs are normally pitched with spin. The spin axis and ball orientation vary from one type of pitch to the next. Most pitches (4-seam fastballs, curveballs, sliders and others) move as they do because of the “Magnus Effect,” similar to other sports balls. Other pitches take advantage of the baseball’s unique asymmetric “figure 8” stitching pattern, most notably the 2-seam fastball and the knuckleball. These are the focus of this study. A unique feature of our work is that we make in-flight PIV measurements of a pitched ball—without a wind tunnel. A 3-wheeled pitching machine throws the ball with the desired speed, rotation axis and rate. Two-component velocity data are obtained in a plane that either cuts the ball vertically or horizontally and is aligned with the ball direction. The velocity data are of sufficient resolution to reveal boundary layer separation, which is found to be a rich function of the ball speed, boundary layer state, rotation rate, and location of the stitches. For the knuckleball pitches (during which the ball does not rotate significantly), dozens of snapshots are acquired and analyzed allowing statistics to be obtained on separation locations on both sides of the ball. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E17.00002: Transient simulation of a four-seam fastball pitch Emin Issakhanian A transient RANS simulation with dynamic mesh was conducted on a rotating, translating baseball in order to quantify the resulting lift, drag, and moment on the baseball. The simulated pitch is a four-seam fastball, so named because the batter sees four seams for each rotation of the ball. This pitch is design for high speed and lift production to counteract gravity and keep the trajectory straight. As the ball rotates, the seam position moves and creates different flow structures for each angle of rotation. The separation points and wake vortical structures are studied for different baseball orientations. Coefficients of drag, lift, and moment about the rotation axis are calculated relative to rotation angle. These forces are integrated to calculate the trajectory of the pitch. The detailed flow structures around the threads of the seam are also analyzed. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E17.00003: Numerical Investigation of the Effect of Rotational Speed on the Flow past a Golf Ball Jun Ikeda, HyoungChol Kim, Masahide Onuki, Makoto Tsubokura Unsteady aerodynamic forces acting on a rotating golf ball and flow structures were investigated using Large Eddy Simulation combined with the moving boundary method. The computational domain was discretized based on the unstructured high-resolution meshes and the first wall-nearest grid is less than 1 in the dimensionless wall distance y plus. That was because to capture the detailed flow structures near the ball surface and predict aerodynamic forces with high accuracy. The Reynolds number based on the ball diameter and the uniform flow velocity was 1.1×105, which is the supercritical region in a dimpled sphere, and the rotational speed was set to the spin parameter Γ = 0.1. In this study, the focus was on the effect of rotational speed on the same golf ball. As a result, both drag and lift increased as the rotational speed was increased. For the difference of flow structures, it was found that the separation lines changed due to the rotational speed. Moreover, there was a difference in the strength of downwash and a pair of longitudinal vortices generated behind the ball. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E17.00004: Optimal Drag in an Accelerating Rowing Blade Ernst Jan Grift, Naren Balaji, Mark J. Tummers, Jerry Westerweel We report on the drag on an accelerating plate below a water surface that mimics part of the propulsive forces of a rowing blade. The motion of the plate is generated by a dedicated industrial robot that can reach the velocities and acceleration encountered in actual rowing. Measurements of the drag force are combined with flow visualisations and PIV measurements. Here, the depth under the free water surface was varied, as well as the blade acceleration and terminal velocity. It was found that there exists an optimal depth where the drag force exceeds both drag values of the blade touching the water surface and far below the water surface by 50 per cent. This implies that there would be an optimal depth for a rowing blade. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E17.00005: Continuum behavior in cycling pelotons Jesse Belden, Mohammad Mansoor, Aren Hellum, Andrew R Meyer, Rafid Rahman, Christopher Pease, Scott Koziol, Tadd T Truscott Large-scale collective behavior, known to be exhibited by a range of species including birds, insects, fish and even humans, results in complex spatiotemporal patterns. These patterns are prominent in pelotons of cyclists in which densely packed bicycle racers move collectively while trying to preserve energy. The widespread assumption has been that the details of rider arrangement follows primarily from an optimal aerodynamic drafting configuration. However, we have found that the local group structure tends to follow from something more intrinsic to the riders’ sensory systems. The resulting interaction principles cause information to propagate through the group in a manner that can be modeled using continuum mechanics. In this talk, we relate this continuum behavior to the fundamental mechanisms driving interaction and comment on the role of aerodynamics in setting the structure of cycling pelotons. |
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