Flow control
The idea of using compliant coatings for drag reduction was first
introduced 30 years ago based on observations of porpoises seeming to
show off their speed by passing alongside a fast ocean liner in an
effortless glide. The maximum observed swimming speed of dolphins and
their known physiological propulsion efficiency prompted some
biologists to speculate that the dolphin has some means of producing
extensive regions of laminar flow. Aside from the issue of reducing the
drag, compliant coatings are finding increasing use in sound
absorption, vibration reduction and noise shielding. The present
research is aimed at gaining fundamental understanding of the complex
interaction between a deformable structure and a boundary layer flow.
Viscous or skin-friction drag accounts for about half of the total drag on modern aircraft at subsonic cruise conditions. A novel method to substantially reduce skin friction drag in a turbulent boundary layer is investigated. The technique combines the beneficial effects of a longitudinally ribbed surface and suction. The longitudinal roughness elements act as nucleation sites which cause the low-speed streaks to appear above them. Suction is then applied intermittently through longitudinal slots located at selected locations with respect to the roughness elements to alter the low-speed regions and to decrease the bursting. If proved successful, the application of the present innovation on commercial aircraft will result in annual fuel savings of several billion dollars