Study on hydrodynamic characteristics and flow field visualization of multi-blade controllable otter board based on CFD

Traditional otter board controls working depth by changing length of the warp and towing speed, and adjusts working posture by changing fixed joint positions between otter board, warp and sweep line, which involves complex operation. To provide scientific references for the design and research of controllable variable-water-depth otter boards, we designed a multi-blade controllable otter board and employed computational fluid dynamics (CFD) simulation to investigate the effects of the rotation direction and angle (−40°~40°) of blades at different positions (Upper and lower ends) on its hydrodynamic performance. The results reveal that: 1) when the blades were closed, the lift coefficient of the multi-leaf controllable otter board reached its maximum value of 0.88 at an attack angle of 20°; its lift-to-drag ratio peaked at 8.85 at an attack angle of 5°. 2) At an attack angle of 0°, when the blades at both ends of the otter board rotated in a negative direction, the lift gradually decreased to zero and reversed its direction at a rotation angle of −20°; when the blades rotated in a positive direction, the lift coefficient first increased and then decreased, reaching its maximum value of 0.32 at a rotation angle of 20°; the lift-to-drag ratio decreased as the rotation angle increased. 3) At an attack angle of 20°, when the blades at both ends of the otter board rotated in a positive direction, the lift coefficient continuously decreased; when the blades rotated in a negative direction, the lift coefficient first increased and then decreased, reaching its maximum value of 1.05 at a rotation angle of −10°; the lift-to-drag ratio peaked at 5.25 at a rotation angle of −20°. 4) Under the two angles of attack, when the blades at both ends rotated individually in a positive direction, the Z-axis force coefficient increased first and then decreased.