A proper orthogonal decomposition study on the unsteady flow behaviour of a hydrofoil with leading-edge tubercles

Flow behaviour of a hydrofoil with leading-edge tubercles was experimentally studied using particle image velocimetry technique at a Reynolds number of Re=1.4×104. Four angles-of-attack of α=0°, 10°, 15° and 20° were considered. Proper orthogonal decomposition (POD) technique was used to analyse the instantaneous velocity fields and derive information on the variation of corresponding coefficients and flow energy content. Results show that tubercles can alter the vortical behaviour and lead to increased flow unsteadiness. At lower angles-of-attack, the flow behaviour for the baseline hydrofoil is dominated by wake vortex-shedding, which represents a significant percentage of flow energy content. In contrast, separated shear layer and flow reattachment become the dominant flow behaviour for the hydrofoil with tubercles. Higher order POD modes 4 and 5 are associated with coherent vortex convection in the shear layer, which is similar to that of the baseline hydrofoil at higher angles-of-attack. At α=15°, POD modes 2 and 3 along the tubercle trough and peak show coherent vortex-shedding in the flow separation region. However, unstable flow separations are observed along the Mid-plane between the peaks and troughs, as a result of the separated shear layers associated with POD modes 1 and 2.