Index of content:
Volume 13, Issue 8, August 2001
13(2001); http://dx.doi.org/10.1063/1.1381019View Description Hide Description
The decay of large-scale anisotropies in small-scale turbulent flow is investigated. By introducing two different kinds of estimators we discuss the relation between the presence of a hierarchy for the isotropic and the anisotropic scaling exponents and the persistence of anisotropies. By direct measurements on a channel flow numerical simulation we show that the presence of a hierarchy for the isotropic and the anisotropic scaling exponent is not in contradiction with the persistence of anisotropies at small scales.
13(2001); http://dx.doi.org/10.1063/1.1381563View Description Hide Description
Opposition control of near-wall turbulence was carried out using a wall-normal jet from a piston-type actuator, by selectively cancelling the downwash of high-momentum fluid during the sweep events. By employing an innovative methodology we were able to study the effectiveness of the scheme without carrying out real-time control, overcoming experimental difficulties associated with the high-frequency responses required for the turbulence control. Observed changes of the burst signature in the turbulent boundary layer suggest that there is a possibility of reducing the skin-friction drag when opposition control is carried out with appropriate timing.