Date of Award

12-2008

Degree Name

Doctor of Philosophy

Department

Mechanical and Aeronautical Engineering

First Advisor

Dr. William W. Liou

Abstract

Flow separation control is of importance to the performance of air vehicles. Generally, it is desired to postpone separation such that the overall drag is reduced, stall is delayed, lift is enhanced, and pressure recovery is improved. This work explores a new concept of post-stall flow control for airfoils and wings by using a thin flexible fin attached on the upper surface of an airfoil to passively manipulate flow structures in the fully separated flows for drag reduction and lift enhancement. The flow induced oscillations combined with the shape deformations change the overall pressure distribution on the fin, which in turn affect the fin dynamics. This mutual effect of inertial and elastic forces can also be considered through fluid-structure interactions (FSI). In order to study this problem a Navier-Stokes finite difference solver is coupled with a subdivision finite element solver in a segregated manner. The moving interface (i.e. fin) is modeled by a non-boundary conforming method called Immersed Boundary Methods (IBM).

In the present dissertation validations for the Computational Fluid Dynamics (CFD), the Computational Structural Dynamics (CSD) and the Immersed boundary method (IBM) are presented. Then the coupled CFD-CSD solver is first used to model flow induced flapping flat plate with a 5° angle of attack at Re = 20,000. Finally, the coupled solver is used to simulate flow over a NACA0012 airfoil with a passive flexible flapping fin attached to the upper surface of the airfoil with a 18° angle of attack at Re = 63,000. The time averaged drag coefficient around the NACA0012 airfoil with the fin is computed at various angles of attack and compared with the baseline drag coefficient. The results show that the computations follow the experimental trend of drag reduction at higher angles of attack.

Access Setting

Dissertation-Open Access

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Engineering Commons

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