Effect of aspect ratio on hydrodynamic performance of high lift otter board in trawl fisheries

Abstract

Otter board is one of the main component in the production of single boat trawl fisheries. For improving the expansion performance of trawl net in middle-water trawl fisheries, an improved high lift otter board was developed. A flume model experiment was conducted to measure the lift coefficient (CL), drag coefficient (CD) and lift to drag ratio (K) in different angle of attack (α). The experimental results are as follows: (1) The aspect ratio has significant influence on the max lift coefficient (CLmax), the max lift to drag ratio (Kmax), critical angle of attack (α0) and lift to drag ratio at α0 (P<0.01). As the increase of aspect ratio, the CLmax and Kmax value show a trend of increasing at the beginning and then decreasing, Kα0 value reflects an upward trend, but the α0 reflects a declining trend; (2) The H2 otter board (aspect ratio was 1.4) showed a better hydrodynamic performance. When α=27.5°, CLmax was 2.535, in this case CD = 1.424, K=1.780. When α=10°, Kmax was 3.508, in this case CL = 1.660, CD = 0.473. Suggest the best working scope of angle of attack is between 15°∼30°, in which case, CL>2.053 and K>1.578. The mean value of lift coefficient was 2.356 and the mean of lift to drag ratio was 2.329. Through comparative analysis of the hydrodynamic performance of different types of otter boards, the H2 otter board both had good expansion performance and good expansion efficiency, which can provide a reference basis for further optimization of the bottom trawl otter board.