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4.2 Moving and Oscillating Airfoi
4.2移动和振荡机翼
As explained previously, the profile in Darrieus motion is subjected to a stronglyvarying angle of attack and velocity magnitude (see Figure 1b). In order t investigate the aerodynamic forces at a single airfoil, this motion is decomposed in anapproximate way as a combination of rotational and linear oscillation. Neglecting the retardation of the flow due to momentum change at the airfoil, the variation of angle of attack is approximated as
where αmax is the maximal angle of attack (pitching amplitude), ω = λUw/R is the angular velocity of the rotor and t is time. Similarly, the effective wind velocity at the airfoil W may be approximated with as
Equations 3 and 4 may be described with the model depicted with Figure 5. In thestream field Ustream = λUw, the airfoil moves periodically with the period T = 2π/ω.The airfoil velocityxdirection and the angular velocity around the quarter cord point
are respectively:
正如前面所解释的，在大流士动议的档案进行强 不同的攻击角度和速度的大小（见图1b）。为了探讨 在一个单一的机翼的气动力，这项议案是一个近似分解
作为一个组合的旋转和线性振荡方式。忽略的延迟由于动量变化在翼型件的流，攻角的变化，是近似为其中αmax是最大的攻角（俯仰振幅），（ω）=λUw/ R是的转子角速度和t是时间。同样地，在有效风速翼型件的W可以近似地用作为方程3和4与图5所示的模型，可被描述。在流场的USTREAM=λUw，翼型件期间定期移动T =2π/ω。在x方向上的翼型件的速度和角速度季线点周围分别是：
The above described motion is modeled using the mesh deformation technique available in ANSYS-CFX. As shown in Figure 6, the solution domain is pided in
6 sub-domains. The mesh in sub-domain 4 rotates with the angular velocity ω0 and
moves (together with the mesh in sub-domain 3) with the velocity Ux. Sub-domains1 and 6 are defined as stationary and the displacement of sub-domain 4 is compensated with the mesh deformation in sub-domains 2 and 5. The velocity Ustream is prescribed at the inlet boundary and other boundaries are defined as in subsection 4.1. The aerodynamic coefficients are defined in term of the relative wind velocity at the airfoil U = Ustream − Ux. The angle of attack α defined at the rotor is the reversed angle of attack defined in Equation 3. The predicted aerodynamic coefficients are shown in Figure 7. For various λ and αmax, the lift coefficient is plotted together with the lift coefficient of a stationary profile in Figure 7a. The predicted lift coefficients are strongly dependent on the pitching amplitude. As expected, at large angle of attack beyond static stall angle stall delays. The dynamic stall with the hysteresis effect is obvious in all cases. The deviation of lift in the upstroke motion as compared to the static values is not clear and needs to be investigated. Figure 7 shows the predicted drag coefficient for λ = 3.5. It is observed,
that during the hysteresis loop negative drag - the thrust appears.
上述运动是仿照使用网格变形技术 在ANSYS-CFX。正如在图6中示出，该解决方案的域被分成6子域。子域4中的网格一起转动的角速度ω0移动（连同子域3中的网格）的速度UX。子域1和6被定义为固定的和子域4的位移补偿子域2和5中的网格变形。规定的速度USTREAM在入口边界和其他边界被定义为在第4.1。 “升力系数中定义的术语在翼型件的相对风速的U = USTREAM - UX。攻角α限定在转子的反转角度
攻击公式3中定义。在图7所示的预测的空气动力系数。对于不同的λαmax，升力系数与一个固定的轮廓的升力系数一起被绘制在图7a中。预测的升力系数是强烈依赖于投球幅度。正如预期的那样，在大攻角超越了静态失速攻角失速延迟。在所有情况下的动态失速的滞后效应是明显的。的偏差电梯在上冲程运动的静态值相比，目前尚不清楚，需要进行调查。图7示出了对于λ=3.5预测的阻力系数。据观察，在磁滞回线的负面拖累 - 推力出现。