Emerging approaches to flow control in hydrodynamics

Recent developments in two approaches to hydrodynamic flow control are considered. One is concerned with the closed-loop large-scale control of maneuvering of biologically-inspired small underwater vehicles in a disturbed littoral ocean environment. The other is the small-scale closed- and open-loop control of turbulence in a boundary layer developing on the outer surface of an ocean going vehicle. Theoretical and experimental progress made are described. The former type appears to be well amenable to closed-loop active control with the potential payoff of a high degree of precision in maneuvering. In the latter type, an active open-loop control appears to have the best potential for turbulence quieting and drag reduction. The paper is limited to exploratory work