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MCE Ph.D. Thesis Seminar

Thursday, April 14, 2016
1:00pm to 2:00pm
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Guggenheim 133 (Lees-Kubota Lecture Hall)
Unsteady aerodynamics and optimal control of an airfoil at low Reynolds number
Jeesoon Choi, Graduate Student, Mechanical and Civil Engineering, California Institute of Technology,

Opposed to conventional air vehicles that have fixed wings, small birds and insects are known to flap their wings at higher angles of attack. The vortex produced at the tip of the wing, known as the leading-edge vortex, plays an important role to enhance lift during its flight. In this talk, we analyze the influence of these vortices on the aerodynamic forces, and suggest possible improvements to micro-air vehicles performance and efficiency. The flow structure associated with simple harmonic motions of an airfoil are first investigated within great detail and further extended by applying optimal control strategies.

The characteristics of the time-averaged and fluctuating forces are successfully explained by analyzing vortical flow features, such as vortex lock-in, leading-edge vortex synchronization and vortex formation time. Parametric studies designed to increase lift, decrease fluctuations, and maximize energy extraction will be investigated, and the results compared to wind-tunnel experimental data. With these results, a variety of flow control problems using the adjoint method can be implemented to evaluate the sensitivity of various cost functions. Using this approach, we realize the flapping motion of an airfoil resembling that of a flying insect as the solution that maximize lift of a reciprocate airfoil.  Also, in an effort to increase micro-air vehicle's resistance to gusts, optimal angles of the wing are found that minimizes the influence of a passing vortex.

For more information, please contact Jenni Campbell by phone at 626-395-3389 or by email at [email protected].