||This research focus on the dynamic stall about a single airfoil of vertical-axis wind turbines (VAWT) on 2D and unsteady flows by numerical simulation. The simulation has been validated by velocity and vorticity measurements of the experimental data, and analyze with lift coefficient and pressure contours. Besides, this simulation tries to use the concept of Lagrangian Coherent Structures (LCS) and different particle tracks to analyze. This method can evaluate structures of flows effectively, and capture some phenomenon which traditional Eulerian method cannot describe. Furthermore, this research use Lagrangian Coherent Structures to analyze the result of simulation on a pitching airfoil, and use the particle(s) track technics to illustrate more complicated flow structures.|
The result of simulation can capture the dynamic flows effectively on qualitative, and the range of analysis focuses on the first time of decreasing lift coefficient on airfoil. According to the result, the leading edge vortex is the main reason effecting dynamic stall. As the leading edge vortex sheds and is close to the trailing edge, it will cause a trailing edge counterclockwise vortex. This vortex will affect the fluid under airfoils, and the fluid will be attracted to upper airfoil or trailing edge counterclockwise vortex. Until all of vortexes shed from the airfoil, this phenomenon finished, and from this time the lift coefficient will rise again. Besides, the simulation have observed the LCS on the lower surface of the foil can be related to the delay of stall due to the leading edge vortex. The result shows that LCS analysis together with other Eulerian method can help this research to have better understandings of the complexity of the dynamic stall.