Shear Flows, Vortices and Flow Control

This paper describes basic and essential roles of vorticity in shear flows and vortex flows, which are very important to deepen knowledge of complex unsteady characteristics of vortical flows and their control. With reference to mathematical expressions of vorticity and estimation of flow circulation, physical meanings of existence of vorticity in a shear layer are discussed and a quite unconventional and useful concept of understanding the close relation between inviscid fluid dynamics and viscous fluid dynamics is explained, introducing a pioneering work on instability of mixing layer and the recent development of discrete eddy simulation (DES). Three dimensionality of boundary layer separation and vortex shedding are described, showing some visualized flows. And also, the key points of vortical flow control are discussed.