Drag reduction method and surface

A method which comprises:

• (a) providing a device which reduces skin friction drag caused by wall surface bounded shear flow through interference with eddy current formation and interactions near the wall surface which comprises microsteps with a downstream facing face in the surface oriented across a mean flow direction along the wall surface and stepped down in the mean flow direction, wherein the face of each of the microsteps has a height on the order of magnitude of a sublayer thickness, which is about 0.0015 mm or larger and which has a length between the faces of the microsteps which is significantly longer than the height of the microstep and 0.03 mm or larger so that the combination of the face height and the length reduce the shear friction drag of the fluid during flow of the fluid as compared to a smooth wall surface;
• and
• (b) flowing the fluid over the surface in the mean flow direction wherein the microsteps reduce the drag.

A device which reduces skin friction drag caused by wall surface bounded turbulent shear flow of a fluid by controlling the flow characteristics within the wall surface bounded shear flow through interference with eddy current formation and interactions near the wall surface which comprises microsteps with a downstream facing face in the surface oriented across a mean flow direction along the wall surface and stepped down in the mean flow direction to a shoulder downstream of each of the microsteps, wherein a portion of the wall surface adjacent to at least some of the microsteps is adapted to inject a small but sufficient amount of fluid primarily in the mean flow direction of the flow and wherein the injection is phased to the passage of pressure producing eddy currents just downstream of a point of injection of the fluid which eddy currents are detected by a detection means in the shoulder.

A device which reduces skin friction drag caused by wall surface bounded turbulent shear flow of a fluid by controlling the flow characteristics within the wall surface bounded shear flow through interference with eddy current formation and interactions near the wall surface which comprises microsteps each with a downstream facing face in the surface oriented across a mean flow direction along the wall surface and stepped down in the mean flow direction, wherein an expandable means is movable into a cavity below the wall surface downstream of at least some of the microsteps to reduce the volume of the cavity so as to result in the injection of fluid in the cavity into the wall surface turbulent shear flow through an opening immediately adjacent to the face to interfere with the eddy currents and wherein the expansible means is later collapsed allowing the cavity to refill with the fluid.

A method which comprises:

• (a) providing a device which reduces skin friction drag caused by wall surface bounded turbulent shear flow of a fluid by controlling the flow characteristics within the wall surface bounded shear flow through interference with eddy current formation and interactions near the wall surface which comprises microsteps with a downstream facing face in the surface oriented across a mean flow direction along the wall surface and stepped down in the mean flow direction to a shoulder downstream of each of the microsteps, wherein a portion of the wall surface adjacent to at least some of the microsteps is adapted to inject a small but sufficient amount of fluid primarily in the mean flow direction of the fluid and wherein the injection is phased to the passage of pressure producing eddy currents just downstream of a point of injection of the fluid which eddy currents are detected by a detection means in the shoulder;
• and
• (b) flowing the fluid over the surface in the mean flow direction while injecting the fluid wherein the microsteps reduce the drag.