Projects

Gray’s Paradox from 1936, also known as „The dolphin’s secret“, describes the inconsistence between the velocity of the dolphin and its applied muscle power. The dolphin is moving faster as predicted from theory. The reason for the higher velocity is its flexible, visco-elastic skin. On the one hand, the dolphin’s skin has a passive attenuation on the increasing amplitude of convective boundary layer instabilities (Tollmien-Schlichting-Waves). On the other hand, the dolphin’s skin also has an active attenuation caused by blood pressure controlled papillary vessels. Therefore, the skin delays the transition of the laminar boundary layer with low friction to a turbulent boundary layer with high friction. Together with the Technical University of Berlin (aerodynamics and control) and the University of Stuttgart (numerics), a technical model of the dolphin’s skin is developed and investigated in a wind. The visco-elastic character of the foil surface is generated with the help of piezo-polymer actuators. These actuators consist of a thin piezo layer that is casted with liquid polymer. The final design of the actuator can be a simple beam or a much more complex geometry. Several of the actuators are combined to an actuator array and connected with a thin flexible membrane. Additionally, flow sensors are integrated in the array. The sensor-actuator-array is then integrated into an arifoil model such that the membrane is flush with the surface. The displacement of the actuators induces a wave in the near wall area that interferes with the wave caused by the instabilities which is measured by the pressure sensors. With an intelligent control, the two waves interfere destructively and the laminar boundary layer is maintained. The aim of the work at the Lab Design of Microsystems is to develop an intelligent design of the actuator array. This design has to fulfill the high requirements regarding displacement, velocity, frequency behavior, stability, and packing density.