Sungchan Hong

Surface geometry can alter the aerodynamic response of sports balls, but the face orientation of modern volleyballs is often treated as a minor experimental detail. This study examined whether the Mikasa V200W volleyball can be considered aerodynamically neutral with respect to ball face orientation under fixed wind-tunnel conditions. Six panel orientations were tested over 7–35 m/s and grouped into two face types, Face A and Face B. The analysis focused on drag-transition behaviour, aerodynamic moment, lateral-force directionality, short-term inter-record stability and drag–lateral force co-variation in the analysed float-serve-relevant range, defined here as 14–20 m/s ( Re ≈ 1.9–2.7 × 10 ⁵ ). Face B showed an earlier and lower face-group mean drag minimum than Face A ( C _d,min = 0.150 at 19 m/s vs 0.177 at 21 m/s), together with a sharper drag decrease over 13–18 m/s and larger aerodynamic moment magnitudes in the float-serve-relevant speed range. Lateral-force descriptors showed orientation-dependent tendencies but with larger short-term inter-record variability than drag. These descriptive fixed-mounted wind-tunnel data indicate that V200W face orientation is not aerodynamically neutral under the present wind-tunnel conditions and should therefore be controlled or reported in volleyball aerodynamics and float-serve testing.

Surface orientation can influence the aerodynamic response of modern soccer balls, particularly in the drag crisis regime. This study quantified the orientation-dependent aerodynamic characteristics of the FIFA World Cup match ball Trionda using a single specimen and examined how these differences affect simulated flight at sea level and 1500 m altitude. Two reproducible reference orientations were defined: a red-panel-centered orientation (Series A) and a seam-junction-centered orientation (Series B). Each reference orientation was rotated by 0°, 90°, and 180°, resulting in six fixed-orientation conditions. Wind tunnel measurements were repeated three times per condition to obtain drag, lift, and side-force coefficients, and two-dimensional non-spinning flight simulations were performed for representative long-kick and free-kick conditions. All six orientations exhibited drag crisis behavior, but the transition response magnitude, subcritical drag level, and supercritical drag state differed among conditions. The representative transition region occurred at approximately Re = 2.0 × 10⁵ to 2.5 × 10⁵. Among the tested conditions, B-90 showed the lowest full-range mean drag coefficient (0.231), whereas A-90 showed the highest (0.266). In the simulations, lower drag orientations consistently produced longer flight ranges, and the B-90 > A-90 ordering was preserved across representative launch conditions and the expanded parametric comparison. These findings indicate that the aerodynamic response of Trionda cannot be represented adequately by a single mean drag coefficient and that surface orientation should be considered in aerodynamic characterization and flight prediction.

Aerodynamic drag is a key factor influencing performance in high-speed winter sports, and even small reductions in drag may contribute to meaningful improvements in race time. This study investigated the effects of seam position and seam-folding direction on the aerodynamic characteristics of skiwear fabrics using wind tunnel experiments with two simplified models: a cylinder model and a wing-shaped model. In the cylinder model, the seam position directly facing the airflow was defined as 0° and shifted in 30° increments, whereas in the wing-shaped model, the seam was moved rearward from the foremost point in 5 cm increments. The inward-folded portion of the seam was arranged either toward the airflow or opposite to it. Wind tunnel tests were conducted at wind speeds ranging from 40 to 120 km/h, and drag coefficients were calculated from measured drag forces. The results show that aerodynamic drag varied with seam position in both models. In the cylinder model, the lowest drag coefficient was observed at 30° from the front, whereas in the wing-shaped model, the lowest drag was obtained at the foremost seam position (0 cm). At 100 km/h, shifting the seam position from 0 cm to 5 cm increased the drag coefficient by approximately 54.5% in seam type A and 50.0% in seam type B. These findings suggest that seam position may be a potentially relevant aerodynamic design variable in skiwear research, whereas seam-folding direction appeared to be of secondary importance under the present test conditions. However, the present conclusions are restricted to simplified experimental geometries and should not be directly generalized to specific body regions or full-garment systems.

Wind-tunnel experiments were conducted on Trionda, the official match ball of the 2026 FIFA World Cup. Aerodynamic force coefficients derived from these measurements were incorporated into numerical trajectory simulations of kicked balls. The resulting aerodynamic characteristics and simulated flight behavior were compared with those of the four previous World Cup match balls: Al Rihla (2022), Telstar 18 (2018), Brazuca (2014), and Jabulani (2010). Relative to its predecessors, Trionda exhibits a drag crisis at lower flow speeds, consistent with an apparently rougher surface. Although its turbulent-regime drag coefficient is more stable than those of earlier designs, its magnitude is modestly larger. Trajectory simulations therefore indicate the potential for small but perceptible reductions in range for long kicks. This study therefore provides the first aerodynamic characterization of the 2026 FIFA World Cup match ball (Trionda) and places its drag-crisis behavior and flight characteristics in direct quantitative comparison with those of recent World Cup balls examined under identical experimental conditions.

The Impact of Surface Structure Changes on the Aerodynamic Characteristics of Modern Soccer Balls

Eight balls were manufactured with a 3D printer to resemble various types of 32-panel soccer balls. One ball was completely smooth, whereas the other seven possessed various dimple patterns on their surface panels. Seam width and seam depth were also varied. Wind-tunnel experiments were performed to extract aerodynamic coefficients, and also to determine the critical Reynolds number for each manufactured ball. A new surface roughness parameter is introduced, and a fitting formula is presented, which allows for the prediction of the critical Reynolds number if the new parameter is known.

The link between aerosol dynamics and viral exposure risk is not fully understood, particularly during movement and face-to-face interactions. To investigate this, we employed Particle Trace Velocimetry with a laser sheet and a high-speed camera to measure microparticles from a human mannequin’s mouth. The average peak time in the non-ventilated condition (expiratory volume, 30 L; passing speed, 5 km/h) was 1.33 s (standard deviation = 0.32 s), while that in the ventilated condition was 1.38 s (standard deviation = 0.35 s). Our results showed that the peak of viral exposure risk was within 5 s during face-to-face encounters under both ventilated and non-ventilated conditions. Moreover, the risk of viral exposure greatly decreased in ventilated conditions compared to non-ventilated conditions. Based on these findings, considering a risk mitigation strategy for the duration of 5 s during face-to-face encounters is expected to significantly reduce the risk of virus exposure in airborne transmission.

Article: Consideration on size, velocity and path of droplets emitted during running - The Journal of Sports Medicine and Physical Fitness 2023 Jul 10 - Minerva Medica - Journals

Wind-tunnel experiments were performed on Al Rihla, Telstar 18, Brazuca, and Jabulani, official match soccer balls used in the World Cup in 2022, 2018, 2014, and 2010, respectively. Aerodynamic coefficients extracted from wind-tunnel results were used to create computer simulations of trajectories of kicked soccer balls. The newest World Cup ball, Al Rihla, could be kicked for longer range compared to its recent predecessors. But there is also the possibility that knuckling effects at large speeds could be seen in the flights of the new ball kicked with little to no spin. Measurements were made of each soccer ball’s total seam length and seam width and depth. Two different measurement techniques were employed to assist with accuracy. Wider and deeper seams led to smaller critical speeds.

The quantitative relationship between kicking motion and ball behaviour can be easily explained by detecting the impact point and foot posture. In previous studies, the impact point of a kicking foot was difficult to capture using visual tracking. Thus, a virtual surface modelling technique was applied in this study to clarify the differences in the three-dimensional foot speed, impact point and foot posture between straight, curve, and knuckle kicks in soccer, as well as the relationship between the kick motion and ball rotation. An optical three-dimensional motion capture system (VICON) was used to record the kicking motion. The impact points of the straight, curve, and knuckle kicks were found to be centrally located in the instep area, at a lower (more downwards) inside area, and at the medial area between the instep and inside areas of the kicking foot, respectively. Moreover, an impact with a greater ‘swing vector deviation angle (relative to the direction from the impact point to the centre of gravity of the ball)’ is necessary for ball rotation. The impact point detection method employed in this study can be applied to other ball impact estimations beyond soccer kicks.