A Vortex Array Model of the Unsteady Wake of a Periodically Pitching Airfoil
Motivated by recent interest in Unmanned Micro Air Vehicles (UMAVs) aerodynamics, the present study is focused on obtaining a simplified, vortex-array model of the unsteady flow in the wake of an airfoil undergoing small-amplitude but high-reducedfrequency pitch oscillations. The model is used to compute the mean and unsteady velocity field in the wake of a NACA 0012 airfoil executing sinusoidal as well as nonsinusoidal pitch oscillation. The model’s accuracy is assessed by comparison to LDV measurements at chord Reynolds number of 12,000 and a reduced frequency as high as 10. The results demonstrate the ability of the vortex-array model to successfully reproduce the experimentally measured mean and phase-averaged streamwise velocity profiles in the wake of the airfoil. Moreover, by using the model to reconstruct the cross stream mean velocity profile in the wake, the average streamwise force acting on the airfoil is computed for different frequencies and amplitudes of oscillation. The computed force coefficient is found to agree well with computational and experimental data in literature. Subsequent to its verification, the model is utilized to explore the thrust force dependence on parameters of the wake vortex pattern; i.e. circulation and streamwise/cross-flow spacing of the vortices. Insight from this exploration has the potential for providing a rational approach for manipulation of the trailing edge flow in order to obtain desirable force characteristics for flapping-wing UMAVs.
Ahmed Naguib is currently Professor in Mechanical Engineering at Michigan State University. He served as the Associate Chair for the Graduate Program from 2012 to 2014. His BS degree is from Ain Shams University, Cairo Egypt, and Master and Ph.D. degrees are from Illinois Institute of Technology, Chicago, USA. His research interests are in experimental fluid dynamics and associated applications, particularly in the field of turbulence and flow instability physics and control, unsteady aerodynamics as well as development of measurement techniques. Prof. Naguib’s work has resulted in more than seventy conference and journal publications, two book chapters, and three patents. He has also been an Associate Editor of the American Institute of Aeronautics and Astronautics (AIAA) Journal since January 2009 and he was awarded the AIAA Associate Fellow grade in 2012.