Abstract: Measures are disclosed for modifying the boundary layer flow over fluid dynamic surfaces using patterns of riblets which are set at a peak-to-peak spacing substantially less than 80 wall units and which are provided with boundary layer suction means comprising apertures (A) between the riblets for a combinative improvement of boundary layer flow. In a further aspect, riblets are employed in combination with wall apertures as an improved means of shock wave (W) control by permitting recirculation of boundary layer fluid from downstream to upstream of the shock wave.

Abstract: To modify a turbulent boundary layer flow over a surface to reduce its drag, a series of streamwise riblet projections is provided on the surface arranged in a pattern consisting of spaced larger height projections between which are a plurality of smaller height projections The latter inhibit turbulent eddy motions from penetrating deep into the grooves between them and so displace the turbulent motion away from the wall. The larger projections control the longitudinal vortices or streaks that are characteristic of turbulent boundary layer flow and promote energy transfer to the smaller scale secondary vortices associated with the smaller projections.

Abstract: An aerodynamic or hydrodynamic surface is provided with so-called "riblets" for reducing drag by modification of the turbulent boundary layer. The riblets comprises flow-aligned elongate projections of small height. In order to increase their effectiveness in reducing drag, just those parts of the riblets which extend above the height 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 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.

Abstract: To modify a turbulent boundary layer flow over a surface to reduce its drag, a series of streamwise riblet projections is provided on the surface arranged in a pattern consisting of spaced large height projections between which are a plurality of smaller height projections. The latter inhibit turbulent eddy motions from penetrating deep into the grooves between them and so displace the turbulent motion away from the wall. The larger projections control the longitudinal vortices or streaks that are characteristic of turbulent boundary layer flow and promote energy transfer to the smaller scale secondary vortices associated with the smaller projections.

Abstract: An aerodynamic or hydrodynamic surface is provided with so-called "riblets" for reducing drag by modification of the turbulent boundary layer. The riblets comprise flow-aligned elongate projections of small height. In order to increase their effectiveness in reducing drag, just those parts of the riblets which extend above the height 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 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.

Abstract: An aerodynamic or hydrodynamic surface is provided with so-called "riblets" for reducing drag by modification of the turbulent boundary layer. The riblets comprise flow-aligned elongate projections of small height. In order to increase their effectiveness in reducing drag, just those parts of the riblets which extend above the height 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 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.