11:00   PIV/PTV methods and applications IV High-speed synchronized measurements of three-dimensional deformation, flow field, and aerodynamic forces of a square membrane wing Qin-Feng Guo, Jin-Jun Wang Abstract: This paper develops a high-speed synchronous measurement system, including high accuracy three-dimensional deformation measurement (HADM), Particle Image Velocimetry (PIV), and a force transducer. The system is applied to investigate the fluid–structure interaction of a square flexible membrane wing with a sampling frequency of 1100 Hz. The membrane's three-dimensional deformations, mid-span flow fields, and lift fluctuations are examined at an angle of attack of 8° and a Reynolds number of 8.2 × 10^4. The membrane exhibits a second mode vibration along the streamwise direction, with a dominant frequency of 135.8 Hz. It is newly observed that two leading-edge vortices (LEV1 and LEV2) are formed above the membrane as the lift increases from its minimum to maximum value. LEV1 sheds from the leading-edge shear layer, while LEV2 remains attached to the wing surface. When LEV1 and LEV2 coexist above the wing surface, the lift reaches its maximum value. Flow Characteristics of Translating Impinging Inclined Water Jets Sterre Bult, Sedat Tokgoz, Said Alhaddad, Rudy Helmons, Geert Keetels Abstract: Translating impinging water jets play a pivotal role in processes such as rock cutting, sediment removal, and material surface treatment. These jets combine the dynamics of both impinging jets and jets in crossflow—two well-studied configurations in fluid mechanics. However, when the jet simultaneously translates across a surface while impinging at an angle, the resulting flow field becomes significantly more complex and less understood. This study aims to advance the fundamental understanding of these translating impinging inclined jets by characterizing their flow structures under a range of inclination angles and velocity ratios. We utilize full-scale underwater stereoscopic Particle Image Velocimetry (PIV) alongside three-dimensional Computational Fluid Dynamics (CFD) simulations to resolve the flow dynamics. Findings from this study enhance our ability to predict sediment erosion, pressure loading, and mixing behavior under practical jetting conditions. Aerodynamic characteristics changes of official tennis balls on new and worn conditions by fluid analysis and 2D Dynamic PIV Shinichiro Ito Abstract: Tennis balls are composed of a hard rubber core covered with a uniform felt fabric. Repeated impacts during gameplay cause the felt to wear and air to leak, resulting in changes to the aerodynamic properties of the ball. While new balls are used in official games, amateur practice often involves worn balls, which influence flight trajectories due to altered aerodynamic characteristics. Additionally, tennis balls frequently spin during flight and are not always used in pristine condition, prompting a study on the differences between new and worn spinning balls. Key findings include: (1) Minimal differences in fluid forces between official models XT8 and FORT for new balls; (2) Lift coefficient proportional to spin parameter (Sp) for both ball types; (3) Worn XT8 balls showed little change in drag coefficient but a decrease in lift coefficient; (4) Worn FORT balls exhibited increases in both drag and lift coefficients; (5) Wake pattern differences observed through Particle Image Velocimetry (PIV), attributed to variations in felt fluff texture. These results highlight the impact of felt wear on the aerodynamic performance of tennis balls, providing insights into how ball conditions influence gameplay and flight dynamics.

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