Flow Separation and Control

The flow condition at the leading edge governs the dynamic of leading-edge vortex (LEV), which is crucial for understanding the separated flow over an airfoil at high angle-of-attack. Furthermore, with extensive applications in biomimetic flight, the wings encountering high-angle-of-attack situations in an unsteady manner is of great interest. The leading-edge suction parameter (LESP) is a dimensionless metric proposed to quantify the leading-edge flow condition, and is implemented in the LESP-modulated discrete vortex method (LDVM) which successfully predicts the aerodynamics of airfoils in motion. To discern the timing of leading-edge vortex formation, a critical threshold for LESP is chose to indicate the onset of separation. However, it is not obvious that the same framework could be apply to a stationary wing where the separation is not dominated by the motion of the airfoil. We conduct computational fluid dynamics (CFD) simulations for a NACA0012 airfoil at high angle-of-attack, and extract the leading-edge flow quantities from the CFD data. In addition, vorticity flux, which contribute to the formation of vortices above the top surface of the airfoil, is also investigated to reveal the vorticity budget and its relevance to aerodynamic performance. The result should offer insights in future improvements on vortex-based models for separated flows.

Funding acknowledgement

This work is supported by the grant NSTC112-2222-E007003MY3 from National Science and Technology Council, Taiwan.