Lagrangian perspective of airfoil vortex shedding behavior.

摘要

Recent interest in Micro Aerial Vehicles (MAV) has fueled research in academic and government institutions. Numerous opportunities are presented with the use of MAV platforms. Atmospheric, oceanic, and reconnaissance platforms are already planned for MAVs. However, as with all new ideas, the technology must catch up with the concepts. One of the issues with MAVs is that the aerodynamic regime governing their flight is substantially different than for traditional manned or large unmanned aircraft. Instead, their small size and slow speeds puts them in the very low Reynolds number flow regime, similar to the flight of birds and large insects. One of the characteristic features of this flight regime is the vortex shedding.;Utilizing invariant material manifolds, the behavior and structure of fluid mixing in the wake of a low Reynolds number two dimensional airfoil is examined from a Lagrangian view point. The examination focuses on the behavior of flow over an Eppler 387 airfoil at various angles of attack for Reynolds number equal to 60,000. Using specialized software, the invariant material manifolds are identified and used to illustrate the structure of vortex shedding. It is verified that these manifolds control the behavior of fluid particle mixing during vortex formation. Furthermore, it is observed that the manifolds are associated with the location and evolution of hyperbolic and elliptic fixed points. The identification of these manifolds allows us to separate the shed vortices into distinct regions of particle mixing and observe how these regions form far in front of the airfoil leading edge. Finally, the phase plot behavior at several points is examined during the vortex shedding process and found to behave in a generally periodic manner.