Flow pressure evaluation on generic surfaces by robotic volumetric PTV

An experimental approach for the measurement of the time-average fluid flow pressure over the surface of generic three-dimensional objects is presented. The method is based on robotic volumetric PTV measurements followed by the integration of the pressure gradient. The domain for pressure evaluation is subdivided in two parts: in the irrotational region the static pressure is obtained following Bernoulli relation; in the turbulent wake and close to the object the pressure gradient is integrated. An approach based on the total pressure distribution is proposed to estimate the boundary between these two regions. The method is first assessed with experiments around a sphere equipped with pressure taps. A criterion for minimum spatial resolution is formulated in terms of maximum ratio between bin size and local radius of curvature of the object. An experimental database from a three-dimensional problem of higher geometrical complexity is considered: the time-averaged flow field around a full-scale cyclist. The surface pressure distribution is discussed in connection to the topological features of near-surface streamlines and streamwise vortices.