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Starting vortex, separation bubbles and stall: a numerical study of laminar unsteady flow around an airfoil

Published online by Cambridge University Press:  29 March 2006

Unmeel B. Mehta  and
Zalman Lavan
Unmeel B. Mehta
Affiliation:
Mechanics and Mechanical and Aerospace Engineering Department, Illinois Institute of Technology, Chicago Present address: Computational Fluid Dynamics Branch, Ames Research Center, NASA, Moffett Field, California 94035.
Zalman Lavan
Affiliation:
Mechanics and Mechanical and Aerospace Engineering Department, Illinois Institute of Technology, Chicago
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Abstract

The stalling characteristics of an airfoil in laminar viscous incompressible fluid are investigated. The governing equations in terms of the vorticity and stream function are solved using an implicit finite-difference scheme and point successive relaxation procedure. The development of the impulsively started flow, the initial generation of circulation, and the behaviour of the forces at large times are studied.

Following the impulsive start, the lift is at first very large and then it rapidly drops. The subsequent growth of circulation and lift is associated with the starting vortex. After incipient separation, the lift increases owing to enlargement of the separation bubble and intensification of the flow rotation in it. The extension of this bubble beyond the trailing edge causes it to rupture and brings about the stalling characteristics of the airfoil. Subsequently, new bubbles are formed near the upper surface of the airfoil and are swept away. The behaviour of the lift acting on the airfoil is explained in terms of the strength and sense of these bubbles. The lift increases when attached clockwise bubbles grow and when counterclockwise bubbles are swept away and vice versa.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 67 , Issue 2 , 28 January 1975 , pp. 227 - 256
Copyright
© 1975 Cambridge University Press

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