Evaluation of scale effect on hydrodynamic force of V-shaped otter board based on CFD
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摘要: 按相似准则等比例缩小网板构建物理模型测定其水动力,是研究网板水动力特征的主要方式。基于V型网板,利用计算流体力学 (Computational fluid dynamics, CFD) 对比分析了3种尺度比 (1∶2、1∶3和1∶4) 的网板和3种厚度 (2、5和10 mm) 下的升、阻力系数及流场分布,并将其与模型试验结果进行对比,探究不同物理模型尺度对估算网板水动力的影响。结果表明:1) 随着冲角的增加,各尺度的网板阻力系数逐渐增大,升力系数先增大后减小,升阻比逐渐减小;2) 在30°冲角之后,网板后部出现明显的分离涡,造成模拟升力减小;3) 随着网板模型尺度的增大,网板表面边界层分离效果和尾流区流场分离涡逐渐增强,网板升、阻力及升阻比亦呈增大趋势。网板厚度对流场及升、阻力影响较小,最大升力系数相对于模型试验平均误差为4.97%。4) 随着模型尺度增大,网板水动力的预测误差逐渐减小。Abstract: The main way to study the hydrodynamic characteristics of the otter board is to build a physical model to measure its hydrodynamic characteristics based on the similarity law. In this study, we analyzed the lift, drag coefficient and flow field distribution of V-type otter board with three scale ratios (1∶2, 1∶3 and 1∶4) and three thickness (2, 5 and 10 mm), and compared them with the corresponding model test results to explore the influence of different physical model scales on hydrodynamic estimation of the otter boards. The results show that: 1) With the increase of the angle of attack, the drag coefficient of otter board with all scales gradually increased, while the lift coefficient first increased and then decreased, and the lift-drag ratio gradually decreased. 2) When the angle of attack reached 30°, the apparent separation vortex appeared at the back of the otter board, resulting in the decrease of simulated lift force. 3) With the increase of the otter board model scale, the separation effect of the boundary layer on the otter board surface and the separation vortex of the flow field in the wake area gradually increased, and the lift, drag and lift-drag ratio of the otter board also showed an increasing tendency. The thickness of the mesh plate had little effect on the flow field, lift and resistance, and the average error of the maximum lift coefficient relative to the model test is 4.97%. As the model scale increased, the prediction error of hydrodynamic force decreases gradually.
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Key words:
- V-type otter board /
- Scale effect /
- CFD simulation /
- Hydrodynamic /
- Flow field distribution
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表 1 网板编号及试验参数
Table 1. Otter board number and experimental parameters
网板编号
Otter board No.展弦比 λ
Aspect
ratio板面夹角 Γ
Dihedral
angle翼展 L
Wing
span/m翼弦 C
Chord/m面积 S
Area/m2厚度 d
Thickness/
mm尺度比 λ
Scale
ratio试验流速
Tested velocity/
(m·s−1)雷诺数
Reynolds
number1 0.5 10° 0.232 0.464 0.102 2 1∶3 0.80 2.1×105 2 0.5 10° 0.350 0.690 0.240 2 1∶2 1.17 2.1×105 3 0.5 10° 0.174 0.348 0.060 2 1∶4 0.60 2.1×105 4 0.5 10° 0.232 0.464 0.102 5 1∶3 0.80 2.1×105 5 0.5 10° 0.232 0.464 0.102 10 1∶3 0.80 2.1×105 表 2 不同尺度比网板水动力系数误差
Table 2. Hydraulic coefficient deviation of different scale ratio of otter board
尺度比 Scale ratio 1∶2 1∶3 1∶4 最大升力系数 Max lift coefficient 1.235 1.178 1.109 误差 Deviation 1.13% 6.03% 12.62% 最大阻力系数Max drag coefficient 1.211 1.138 1.068 误差 Deviation 1.48% 7.99% 15.07% 表 3 不同厚度网板水动力系数误差
Table 3. Hydraulic coefficient deviation of different thickness of otter board
厚度 Thickness/mm 2 5 10 最大升力系数 Max lift coefficient 1.178 1.208 1.184 误差 Deviation 6.03% 3.39% 5.49% 最大阻力系数 Max drag coefficient 1.138 1.134 1.146 误差 Deviation 7.99% 8.37% 7.24% -
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