Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Effect of Deflection Angles on Fluid Performances of Oval-cambered double-sotted Otter Boards
Panpan Jia, Cheng Zhao, Detang Li,Qi Xu,Yonghe Xie*

School of Naval Architecture and Maritime, Zhejiang Ocean University
Zhoushan city, Zhejiang province, China

rectangular otter board, and it is not easy to insert into soft mud in thetrawl. However, there are few studies on the hydrodynamic performanceof the Oval-Cambered Double-Slotted Otter Board. Sivells and Neely(1947) showed that the installation of adjustable devices canconsiderably improve the CL (CL is the lift coefficient) and K (K is liftto-drag ratio) of the wing, such as the installation of leading-edge flaps,split flaps, and trailing-edge flaps at suitable positions. When theleading-edge flap angle is approximately 25°, the airflow passes throughthe wing flaps, the effect of increasing the wing end flow velocity is moreevident, and the effect of reducing the tip vortex is the best. Chen et al.
(1980) showed that when using oval-curved otter boards, a slit can beopened between the front and rear main plates, and two deflectors withaspect ratio λ = 3.6 and relative concavityf = 12% (f =f/l, f represents
the maximum curvature, l represents the wing span length) are inserted
in the middle of the slit to reduce the resistance and enhance the lift ofthe otter boards. McAlister (1991) noted that the thickness and aspectratio are the main factors affecting the fluid dynamics of the wing. Whenthe aspect ratio γ < 0.75, aspect ratio is the main factor affecting the fluiddynamics of the wing. Guo et al. (2008) showed that the oval-curved
otter board used in the early days was curved otter board with an ironwood structure designed by the former Soviet Union. In order to increase
the expansion efficiency of otter board, it is designed as a wing section,
but the vortex at the tail of the otter board is very large. Therefore, a slit
is opened at the front of the otter board, thereby reducing the influenceof water flow on the surface and the resistance of the otter board. Liu etal. (2015) showed that the hydrodynamic performance of the doublecurved slotted otter board was better than the single slotted curved otter
board in a flume tank research experiment at the Chinese Academy ofFishery Sciences. Xu et al. (2017a) studied the hydrodynamicperformance of rectangular V-type otter boards using a wind tunnel andflume tank experiment, and they obtained the maximum K value of theotter board is 3.7. The above experiments not only verified that theseparation of the water flow of the double-flow deflector structure canplay a delayed role. At the same time but also concluded that thedifference of fluid medium will cause the vortex around the otter board
to be very different. Considering that the otter board is running in water,
it is recommended to use numerical simulation or flume tank experiment
to study the hydrodynamic performance of the otter board.

ABSTRACTOval-cambered double-slotted otter boards have various applications in
trawl fishing; however, no extensive studies have been conducted on thefront, middle, and backflow defector angles of the Oval-cambered
double-sotted otter boards. The formula is applied to the oval-camberedotter boards via computational fluid dynamics. The simulations areconsistent with the previous experiments. During trawl fishing at large
angles, when the front, middle, and backflow defector angles of theOval-cambered double-sotted otter boards respectively are 28°, 26° and11°, the otter board exhibits the best fluid performance.

KEY WORDS: Oval-Cambered Double-Slotted Otter Board; Flow
Deflector Angle; Lift-drag ratio; Streamlines; CFD.

INTRODUCTION
An otter board is an important component of trawl fishing systems.
During the fishing, the otter board is used to be expanded the fishing net
in the horizontal direction, and then cooperate with other fishing gear tofully open the fishing net. Therefore, it is crucial to study the otter board.
Bao-Sheng et al. (2006) carried out a rial of performance between therectangular V-shaped curved otter board and V-shaped curved otterboard, and got a conclusion that the performance of the rectangular Vshaped curved otter board is better than V-shaped curved otter board.
Takahashi et al. (2015) applied a numerical simulation method to analyze
the hydrodynamic performance of a biplane-type otter board andconcluded that the maximum lift coefficient (CLmax) is 1.65 when theangle of attack (AOA) is 17.5°, which agrees with experimental resultsthat when the angle of attack (AOA) is 20°, the CLmax is 1.64. CFD wasused to model the acceleration and vertical displacement of the flow inthree dimensions, and the authors then compared the results with windtunnel measurements conducted on the models of two Canadian researchships by Yelland et al. (1998). Sadat-Hosseini et al. (2013) applied CFD
method to analysis the local flow of vessel and get that the added
resistance is mainly induced by high pressure acting on the upper bow.
Nowadays, oval-cambered double-slotted otter boards are suitable for
middle and bottom trawl fishing, its performance is better than the3639