Robotic Volumetric PIV measurements of a full-scale swimmer’s hand

The flow field around a full-scale swimmer’s hand model with varying thumb positions is investigated by robotic volumetric PIV. The experiment is conducted in the Open Jet Facility wind tunnel at TU Delft at 15m/s. Quantitative flow field information is constructed with 3D-PTV in a 120 liter volume, encompassing the full hand and arm. The effect of spatial resolution on the time-averaged flow field is investigated. A large-scale recirculating wake behind the hand is accurately identified at a linear bin size of 20mm whereas the accelerated flow between individual fingers can only be resolved at bin sizes below 10mm where 5mm results in a statistically unconverged velocity field. The influence of the thumb is limited to one side of the hand where its presence results in a larger stagnated region in front and larger wake behind the hand, depending on the thumb position. Closing the thumb strengthens the recirculation but results in a smaller velocity deficit downstream, suggesting a smaller propulsive force generation which is considered disadvantageous in competitive swimming.