Some Advances in Reducing Drag and Suppressing Convection

Naval Research Laboratory, Washington, DC

Friday, June 01 2007

Properly designed upstream-traveling suction/blowing waves could reduce drag.

Theoretical and computational research has yielded some advances in the art of designing active feedforward and feedback controllers to suppress thermal convection and reduce drag (by suppressing turbulence) in boundary-layer flows. The advances include (1) improved means for designing reduced-order (and, hence, computationally more efficient) controllers and (2) discovery of a previously unknown phenomenon that could be exploited for feedforward control to reduce drag.

The mathematical model used in this research is that of three-dimensional flow of a viscous, incompressible liquid in a channel bounded by flat, parallel upper and lower walls, with three parallel sensor planes embedded in the channel and actuator planes coinciding with the walls (see figure). The actuation consists of a combination of blowing or suction normal to the upper wall and an equal amount of suction or blowing, respectively, normal to the lower wall at the same streamwise (horizontal) location so that there is no net transfer of mass into or out of the channel. Both sensing and actuation are assumed to be temporally continuous and spatially continuous on the affected planes.