Assessment of flow characteristics around twin rudder with various gaps using PIV analysis in uniform flow

We carried out a twin-rudder performance test in a circulating water channel using particle image velocimetry (PIV). We set the distance between two single rudders to 0.5C, 0.75C, and 1.0C, where C is the chord length (C=100 mm), and considered angles of attack of 10°, 20°, and 30°, respectively. A two-frame gray-level cross-correlation PIV method was used to obtain flow information. The twin-rudder model was constructed using a submerged NACA 0018 airfoil with a row arrangement. Throughout the experiments, the Reynolds number of the NACA 0018 airfoil was kept at 1.5×104. The measured results were compared with results of each case involving a single rudder. For the single rudder, flow visualization, time-mean velocity fields, and vorticity information were measured at angles of attack of 10°, 15°, 20°, and 25°. For the twin rudder, streamlines, instantaneous and time-mean velocity fields, vorticity, and turbulence intensity were measured and compared with each other to determine the critical distance between the single rudders. It was found that this critical distance should be less than 1.0C in order to decrease turbulence flow and vortices.