Experimental Investigation of Spanwise-Equidistant Spinning Disks for Control of Crossflow-Dominated Laminar-Turbulent Transition

Kurzfassung

A new method for the artificial excitation of stationary crossflow instabilities with controllable amplitude is presented and investigated. Spinning disks, integrated flush into the surface of a flat-plate wind-tunnel model and arranged equidistantly in spanwise direction, are used to introduce specific disturbances into the boundary layer. The excitation of such disturbances is of particular interest in the context of the Upstream Flow Deformation strategy for delaying crossflow-dominated transition. In this flow-control technique, an additional artificially excited control mode is used to nonlinearly deform the spanwise-averaged boundary-layer flow field with an overall stabilizing effect. It is shown that a stationary crossflow instability with well-defined spanwise wavelength is successfully excited and that its amplitude can be controlled by the rotational frequency of the disks. Nevertheless, a delay of laminar-turbulent transition could not be achieved yet, most likely because an unwanted additional excitation of unsteady disturbances was observed. However, some evidence is provided that this unwanted unsteady excitation is not inherent to the presented actuation concept and may be significantly reduced by an improved technical implementation.