Experimental and numerical studies on moderate-Re aerodynamics of cambered thick wingsails in crescent shape

For wind-assisted ship propulsion (WASP), wingsails with cambered sectional profiles like crescent-shaped ones have shown great potential considering high thrust generation. However, there have been few experimental and numerical studies to address such wingsails at moderate Reynolds numbers (Re), of which the knowledge is important for guiding fast design. In this study, the aerodynamics of a classical crescent-shape wingsail at a range of low Re is investigated in isolated and triple-sail situations. Wind tunnel tests and high-fidelity computational fluid dynamics (CFD) simulations, which use the improved delayed detached Eddy simulation (IDDES) approach, are conducted. The wingsails of two aspect ratios (0.19 and 0.33 corresponding to semi-retracted and fully expanded sails in practice) are analyzed at the angles of attack from 0° to 90°, and Re from 1.8×10^5 to 3.6×10^5. In addition to general aerodynamic characteristics, a specific crisis of the aerodynamic forces is found at 15° when Re is reduced to 2.7×10^5, which does not exist in conventional NACA-profile wingsails. When triple wingsails are arranged in a row, the pressure field between the wingsails is interfered although the vortex patterns in the wakes are similar. This interference leads to changes in the aerodynamic forces.