21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-3.4.3

THE MECHANISM OF ACTIVE BOUNDARY LAYER CONTROL USING VORTEX GENERATOR JETS

Hasegawa H., Matsuuchi K., Yamakami J.
University of Tsukuba, Japan

Keywords: active boundary layer control, vortex generator jets

The vortex generator jet method is an active control of flow separation that has the ability to provide a time-varying control action to optimize performance under a wide range of flow conditions. Pitched and skewed jets issue into a free stream and the interaction between the jets and the free stream generates longitudinal (streamwise) vortices. The mechanism for suppressing flow separation was studied experimentally by making a comparison between two effects of steady and pulsed jets on generating longitudinal vortices. The suppression of flow separation is accomplished by the secondary flow ·of longitudinal vortices which transport high momentum fluid of the free stream to the lower wall. However, if the vortex moves away from the lower wall, a counter-rotating vortex of nearly equal strength is induced, and thus an upwash region is produced by the effect of a vortex pair. The upwash makes ineffective the secondary flow toward the lower wall. Consequently, the boundary layer thickness is strongly distorted and is not uniform in the spanwise direction because streamwise velocity decreases near the outer edge of the boundary layer. Pulsed jets enhance the mixing process in comparison with steady jets and indicate effective separation control for the purpose of keeping the vortex near the lower wall.

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