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摘要:
采用求解Navier-Stokes方程的数值方法研究了翼型NACA4412近距离经过波浪水面时的气动特性。对数值方法的准确性进行了验证。计算了翼型经过波浪水面和固壁波浪地面2种边界条件下的气动力系数，并进行了对比。研究结果表明：翼型在经过波浪水面时气动力系数会发生周期性的变化，与固壁波浪的情况相比，气动力的变化曲线存在显著差异，波动幅度更大。通过对流场结构的分析，发现了翼型和波浪水面之间的作用机理。波浪水面的质点存在竖直方向上的运动，在小地面间隙时，水面质点向上运动会挤压翼型和水面之间的空气，从而造成翼型气动力大幅波动。同时解释了来流速度越大，气动力系数波动幅度减小的原因。
Abstract:The aerodynamic characteristics of NACA 4412 airfoil moving over wavy water at small clearance is studied by solving Navier-Stokes equations. The accuracy of the numerical method is verified. The aerodynamic coefficients of airfoil moving over wavy water surface and wavy ground are calculated and compared. The results show that the aerodynamic coefficient changes periodically when the airfoil moves over the wavy water surface. Compared with the case of wavy ground, the variation curve of aerodynamic coefficient is significantly different and the fluctuation amplitude is larger. Through the analysis of the flow field structure, the interaction mechanism between the airfoil and the wavy water surface is found. The particles on the wavy water surface have vertical motion, when the clearance is small, the upward movement of the particles on the water surface will squeeze the air between the airfoil and the water surface, resulting in a large fluctuation of the airfoil aerodynamic force. At the same time, the reason why the fluctuation amplitude of aerodynamic coefficient decreases with the increase of incoming flow velocity is explained.
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Key words:
- wave /
- ground effect /
- aerodynamic amplitude /
- flow mechanism /
- squeezing effect
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图 3 压力系数的计算值和试验值对比
Figure 3. Comparison of computed and experimental pressure coefficient
图 4 波形计算结果与理论结果对比
Figure 4. Comparison of calculated and theoretical results of waveform
图 5 不同来流速度下2个周期内气动力系数变化
Figure 5. Variation of aerodynamic coefficient in two cycles at different velocities
图 8 水面质点在水平和垂直方向上的运动速度
Figure 8. Horizontal and vertical velocity of particles on water surface
图 9 不同时刻翼型表面压力系数分布
Figure 9. Pressure coefficient distribution on airfoil at different moments
图 12 翼型下方水面质点垂直方向运动速度
Figure 12. Vertical velocity of particles on water surface below airfoil
图 14 来流速度为100 m/s时2种边界条件的气动力系数对比
Figure 14. Comparison of aerodynamic coefficient between two boundary conditions at velocity of 100 m/s
表 1 实验值与不同网格数量下的计算结果
Table 1. Calculation results with different grid numbers
网格 网格数 Y+ 升力系数Cl 阻力系数Cd 实验值 0.858 2 0.010 9 疏网格 127 188 2 0.874 90 0.011 88 中等网格 209 127 1 0.874 96 0.011 87 密网格 311 121 0.5 0.874 66 0.011 78 
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表 2 不同来流速度对应的雷诺数和弗劳德数
Table 2. Re and Fr corresponding to different velocities
来流速度/(m·s-1) Re/106 Fr 30 1.0 13.5 40 1.4 18.1 50 1.7 22.6 70 2.4 31.6 100 3.4 45.2
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