浸没边界耦合格子玻尔兹曼方法研究拍抛运动流场
Investigation of flow field of clap & fling motion using immersed boundary coupled lattice Boltzmann method
摘要：
本文采用浸没边界与格子玻尔兹曼方法耦合的方法，研究了由拍击和甩击机制引起的流场。格子玻尔兹曼方法（LBM）是一种可替代Navier-Stokes方程的方法，由于其在求解复杂的移动边界问题时的简单性和计算效率而被使用。对两个展弦比为5的椭圆机翼在不同雷诺数（Re = 75，100，150）、前进比（J = 10 E-3，10 E-2，2）和频率（f = 0.05Hz，0.25Hz）下进行拍拍和甩拍运动的绕流进行了数值模拟。数值模拟能够捕捉到典型的低雷诺数非定常现象，如“尾涡-机翼干扰”、“Kramer效应”和“延迟失速”。计算结果与实验观察在定性和定量上都是一致的。涉及Re、f和J的不同组合的参数研究描绘了明显不同的空气动力学性能，提供了对流动物理的物理见解。观察到低f、低J和高Re流的组合导致更好的气动性能。与准定常状态（J>1）相比，在非定常状态（J<1）下通过前缘涡获得了显著的升力增强。通过研究不同来流条件下前缘涡的大小和强度，研究了前缘涡在增升中的作用。对于给定的Re，最大升力系数的大小随f的增大而减小，与J的值无关;而随着Re的增大，最大升力系数的大小随f的增大而增大。
英文摘要：
This paper deals with the investigation of flow field due to clap and fling mechanism using immersed boundary coupled with lattice Boltzmann method. The lattice Boltzmann method (LBM), an alternative to Navier Stokes solver, is used because of its simplicity and computational efficiency in solving complex moving boundary problems. Benchmark problems are simulated to validate the code, which is then used for simulating flow over two elliptic wing of aspect ratio 5 performing clap and fling flapping motion for different flow parameters such as Reynolds number (Re = 75,100,150), advance ratio (J = 10E-3,10E-2,2) and frequency (f = 0.05Hz,0.25Hz). Numerical simulation is able to capture typical low Reynolds number unsteady phenomena such as, 'wake vortex wing interaction', 'Kramer effect' and 'delayed stall'. The results are both qualitatively and quantitatively consistent with experimental observation. The parametric study involving different combinations of Re, f and J depict distinctly different aerodynamic performances providing physical insights into the flow physics. It is observed that a combination of low f, low J and high Re flow results in better aerodynamic performance. Pronounced lift enhancement via leading edge vortices are obtained in unsteady regime (J<1) compared to quasi-steady regime (J>1). The role of leading edge vortices in enhancing lift are investigated by studying the size and strength of these vortices for different flow conditions. For a given Re, the magnitude of maximum lift coefficient decreases with increasing f irrespective of the value of J; while the same is enhanced with the increasing Re.
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