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Critical Angle and Fundamental Frequency of Symmetric Airfoils at Low Reynolds Numbers
Author(s): Funda Kurtulus
Keywords: Micro air vehicles; vortex shedding; unsteady aerodynamics
The unsteady vortex evolution of NACA 0012 airfoil is numerically investigated at low angles of attack ranging from 0 deg to 10 deg where the separation is performed from the trailing edge. The Reynolds number ranges between 1000 and 4000. The laminar separation bubble at the trailing edge is observed and the main flow features are presented. It is found that, the increase of the angle of attack and Reynolds number result higher lift to drag ratio. The transition from the steady condition to periodic force evolution has been revealed with a detailed flow field analysis at different angles of attack and Reynolds numbers. The critical angle is defined as the angle of attack where the onset of oscillations starts with a dominant fundamental frequency of oscillation. The angle of attack where the laminar separation bubble (LSB) is observed is also revealed in the current study. A pulse frequency is detected for the angles of attack lower than this critical angle where the laminar separation bubble did not still shed. Both the LSB formation angle and critical angle is found to decrease with the increase of the Reynolds number.

Journal of Applied Fluid Mechanics

The Journal of Applied Fluid Mechanics (JAFM) is an international, peer-reviewed journal which covers a wide range of theoretical, numerical and experimental aspects in fluid mechanics. The emphasis is on the applications in different engineering fields rather than on pure mathematical or physical aspects in fluid mechanics. Although many high quality journals pertaining to different aspects of fluid mechanics presently exist, research in the field is rapidly escalating.