Coherent and turbulent process analysis of the effects of a longitudinal vortex on boundary layer detachment on a {NACA0015} foil

Abstract

In the present paper, interactions mechanism of the propeller hub vortex with the rudder installed in its wake are studied. This configuration corresponds to the field of marine propulsion allowing specific problem such as cavitation inception, modification of the propulsive performances and induced vibrations. To better understand the complex mechanisms due to the impact of the propeller-rudder interactions decided to put more emphasis onto configuration where the hub vortex is generated by an elliptical 3D foil and is located upstream the 2D NACA0015 foil at high incidences at Reynolds number 5 105. The physical mechanism involved in the interactions between a single longitudinal vortex and boundary layer detachment was studied using time resolved stereoscopic PIV techniques. Particular attention was paid to the detachment at 25° incidence and a detailed cartography of the mean and turbulent properties of the wake is proposed. The proper orthogonal decomposition (POD) analysis was applied in order to highlight the unsteady flow aspects using phase averaging based on the first POD coefficients to characterize the turbulent and coherent process in the near wake of the rudder.