Investigation Of 3D Effects And Free-Surface Proximity Influence On The Flow Around A Hydrofoil Using PIV Measurements

Abstract

An Eppler 817 (E817) hydrofoil was studied experimentally using two dimensions two components Particles Image Velocimetry (PIV) measurements. Both statistical and time-resolved series were used to study the effect of Reynolds number and angle of attack on the flow topologies and dynamics. Vortex shedding modes were observed over a range of low chord-based Reynolds numbers 400 ≤ Rec ≤ 20000 and four angles of attack ( α = 2◦, 6◦, 12◦ and 30◦). Those Reynolds numbers are scarce documented on such hydrofoil as they are far from usual operating conditions. However, those low Reynolds numbers allowed us to observe Reynolds number based transitions of the vortex shedding modes at a given angle of attack. The data were acquired on both an extruded 2D hydrofoil and a 3D "T-shaped" hydrofoil, composed of a vertical shaft (e.g. rudder on a boat) holding the horizontal lifting surface. The latter was used to investigate the influence of both the 3D shape and surface proximity on the hydrofoil’s behaviour through three different depths, ranging from 3.5 to 0.875 chords. Additional measurements from a 6-axis loads sensor were used to characterize the loss of performance due to the free-surface proximity.