| 摘要 |
An aerodynamic or hydrodynamic surface is provided with so-called "riblets" (R,r) for reducing drag by modification of the turbulent boundary layer. The riblets (R,r) comprise flow-aligned elongate projections of small height (hL<+>, h<+>). In order to increase their effectiveness in reducing drag, just those parts of the riblets which extend above the height ( 3/4 h<+>) of the virtual surface - established by the riblets themselves due to their displacing the turbulent motion away from the real surface - exhibit an abrupt transition (t) to a cusp-shaped profile which more effectively promotes very small scale flow-aligned vortices which drain energy from the larger drag-inducing low speed flow-aligned vortices or "streaks" in the boundary layer. |
