Micro-array surface for passive drag modification

An aerodynamic or hydrodynamic wall surface configured to modify the interaction of a boundary layer of a fluid flowing across the wall surface, comprising:

• at least one array of roughness elements disposed on and extending from the wall surface, the array of roughness elements are positioned in successive ridges of roughness elements, wherein each ridge of roughness elements is positioned substantially transverse to the flow of fluid across the wall surface, and wherein each ridge of roughness elements forms a substantially saw tooth pattern of roughness elements having a selected wavelength,
• wherein each roughness element extends outwardly from the wall surface at one or more selected angles relative to the flow of fluid across the wall surface such that a preferential flow direction surface is formed, the at least one selected angle comprises acute angles,
• wherein each roughness element has a front, upstream surface and an opposing rear, downstream surface and a peripheral edge that has an upper portion that tapers to a top and a bottom portion that tapers to a base, which is connected to the wall surface, the front, upstream surface having a curved, concave cross-sectional shape relative to the flow of fluid toward the front surface, and the rear, downstream surface having a curved, concave cross-sectional shape relative to the flow of fluid toward the rear surface that is configured to promote recirculation of the flow within the cavity and to act as a streamlining effect in both stabilizing and promoting an embedded vortex flow field,
• wherein a plurality of roughness elements are positioned substantially transverse to the flow of fluid across the wall surface such that a distance between a medial portion of the peripheral edges of adjacent and aligned roughness elements is less than the distance between the respective tops of the roughness elements and is less than the distance between the respective bases of the roughness elements,
• wherein the array of roughness elements defines a plurality of cavities,
• wherein the preferential flow direction surface is configured for passively resisting flow adjacent the wall surface that is flowing in a direction toward the rear surface,
• wherein each roughness element comprises at least one riblet extending outwardly from the front, upstream surface, the at least one riblet being configured to aid in the formation and stability of cavity flows embedded between the roughness elements, and
• wherein each roughness element comprises at least one riblet extending outwardly from the rear, downstream surface of the roughness element, and wherein each rear surface extending riblet extends substantially longitudinally.