초록 ▼

The present invention is directed to a micro-array surface that provides for either drag reduction or enhancement. In one aspect, an aerodynamic or hydrodynamic wall surface that is configured to modify a fluid boundary layer on the surface comprises at least one array of roughness elements disposed

The present invention is directed to a micro-array surface that provides for either drag reduction or enhancement. In one aspect, an aerodynamic or hydrodynamic wall surface that is configured to modify a fluid boundary layer on the surface comprises at least one array of roughness elements disposed on and extending therefrom the surface. In one example, the interaction of the roughness elements with a turbulent boundary layer of the fluid reduces the skin friction drag coefficient of the surface over an identical smooth surface without the roughness elements.

대표청구항 ▼

1. An aerodynamic or hydrodynamic wall surface configured to modify the interaction of a boundary layer of a fluid with the wall surface, comprising: at least one array of roughness elements disposed on and extending therefrom the surface, wherein each roughness element has a front, upstream surface

1. An aerodynamic or hydrodynamic wall surface configured to modify the interaction of a boundary layer of a fluid with the wall surface, comprising: at least one array of roughness elements disposed on and extending therefrom the surface, wherein each roughness element has a front, upstream surface and an opposing rear, downstream surface, wherein each roughness element has 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, wherein each roughness element is positioned adjacent and aligned substantially transverse to the flow of fluid across the 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 a distance from the front surface to the rear surface in the medial portion of each roughness element is greater than the distance from the front surface to the rear surface in the upper portion and the bottom portion of each roughness element, wherein a peak longitudinal height of each roughness element is greater than a peak width of each roughness element, wherein the width of the medial portion of each roughness element is greater than the width of the upper portion and the bottom portion of each roughness element, wherein the array of roughness elements defines a plurality of cavities, and wherein the thickness of the boundary layer is in a range of 10% to 30% of a cavity height of each cavity such that shear layer instabilities of cavity vortexes that form therein the plurality of cavities are reduced. 2. The wall surface of claim 1, wherein each formed cavity vortex has a Re in the range of between 100 and 20,000, relative to the cavity height, velocity of the fluid over the wall surface, and the kinematic viscosity of the fluid, such that the instability of the formed cavity vortexes are suppressed. 3. The wall surface of claim 1, wherein each formed cavity vortex has a Re in the range of between 1,000 and 5,000, relative to the cavity height, velocity of the fluid over the wall surface, and the kinematic viscosity of the fluid, such that the instability of the formed cavity vortexes are suppressed. 4. The wall surface of claim 1, wherein the roughness elements extend substantially normal to the wall surface. 5. The wall surface of claim 1, wherein a transverse longitudinal height of the roughness element has a range of between about 0.001 to 2.00 cm. 6. The wall surface of claim 1, wherein adjacent roughness elements within a ridge of roughness elements have different scaled dimensions, such that the formed ridge has a staggered saw tooth appearance. 7. The wall surface of claim 1, further comprising a means of interlocking a plurality of formed cavity flows, formed between the respective roughness elements, together in a substantially chain-link type array of streamlines that are relatively stable. 8. The wall surface of claim 1, wherein the array of roughness elements are positioned in successive ridges of roughness elements. 9. The wall surface of claim 8, 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. 10. The wall surface of claim 9, wherein the distance between adjacent successive ridges is in a range between about 45 to 55% of the peak longitudinal height of the roughness elements. 11. The wall surface of claim 9, wherein each roughness element has a substantially diamond cross-sectional shape relative to a plane transverse to the flow of fluid over the wall surface. 12. The wall surface of claim 9, wherein each roughness element has a substantially oval cross-sectional shape relative to a plane transverse to the flow of fluid over the wall surface. 13. The wall surface of claim 9, wherein the roughness elements in adjacent ridges of the array are positioned offset from each other relative to the flow of fluid across the surface. 14. The wall surface of claim 9, wherein each ridge of roughness elements of the array has a saw tooth wavelength that is substantially equal to an optimal perturbation wavelength for the shear flow inside the boundary layer. 15. The wall surface of claim 9, wherein one cavity of the plurality of cavities is formed between adjacent successive ridges of roughness elements. 16. The wall surface of claim 15, wherein the distance between adjacent successive ridges is in a range between about 40 to 60% of the peak longitudinal height of the roughness elements. 17. The wall surface of claim 9, wherein a portion of the respective peripheral edges of the adjacent and aligned roughness elements in a ridge of roughness elements are connected and define a channel between portions of the bases and the bottom portions of the peripheral edges of the adjacent and adjoined roughness elements. 18. The wall surface of claim 17, wherein each channel extends longitudinally substantially co-axial to the flow of the fluid across the wall surface. 19. The wall surface of claim 9, wherein the front, upstream surface of each roughness element has a curved, convex cross-sectional shape relative to the flow of fluid across the wall surface. 20. The wall surface of claim 19, wherein the rear, downstream surface of each roughness element has a curved, concave cross-sectional shape relative to the flow of fluid that is configured to promote the recirculation of the flow within the cavity and to act as a streamlining effect in both stabilizing and promoting an embedded vortex flow field. 21. The wall surface of claim 20, wherein the top of each roughness element is positioned at an acute angle relative to the wall surface such that the tops of the roughness elements do not protrude into the fluid flow substantially normal to the flow direction. 22. The wall surface of claim 20, wherein a radius of curvature of the rear, downstream surface of the roughness element is less than a radius of curvature of the front, upstream surface of the roughness element. 23. The wall surface of claim 20, wherein each roughness element comprises at least one riblet extending outwardly therefrom the front, upstream surface of the roughness element that is configured to aid in the formation and stability of cavity flows embedded between the roughness elements. 24. The wall surface of claim 23, wherein each roughness element comprises at least one riblet extending outwardly therefrom the rear, downstream surface of the roughness element, and wherein each riblet extends substantially longitudinally. 25. The wall surface of claim 24, wherein the top of each roughness element comprises a saw tooth pattern of shorter wavelength superimposed on the larger wavelength saw tooth pattern of the formed ridge of roughness elements such that the formation of optimal perturbations are inhibited due to the instability of the shear flow or boundary layer of the fluid above the roughness element and inside the boundary layer. 26. The wall surface of claim 25, wherein the smaller wavelength superimposed on the larger saw tooth tops has a range of between about ⅓ to 1/7 that of the larger wavelength. 27. The wall surface of claim 23, wherein each riblet extends longitudinally from at or near the bottom portion of the roughness element, proximate the base, to at or near the top of the roughness element. 28. The wall surface of claim 27, wherein each riblet extends substantially transverse to the wall surface. 29. The wall surface of claim 27, wherein the number of riblets is in a range of between about 1 to 7 per each longer wavelength of the saw tooth pattern of the formed ridge of the array. 30. The wall surface of claim 27, wherein the at least one riblet comprises a plurality of riblets. 31. The wall surface of claim 30, wherein a trough is defined therebetween adjacent riblets that arc recessed from the respective tips of the riblets. 32. The wall surface of claim 31, wherein 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, wherein each ridge of roughness elements forms a substantially saw tooth pattern of roughness elements having a selected wavelength, wherein one cavity of the plurality of cavities is formed between adjacent successive ridges of roughness elements, and wherein the distance between adjacent successive ridges is in a range between about 40 to 60% of the longitudinal height of the roughness elements. 33. The wall surface of claim 31, wherein the front, upstream portion of each roughness element has an edge surface that extends between respective riblets that are positioned adjacent to the sides of the roughness element. 34. The wall surface of claim 33, wherein the edge surface is substantially planar. 35. The wall surface of claim 33, wherein at least a portion of the edge surface is curved, and wherein a radius of curvature of the edge surface is greater than a radius of curvature of the trough of the roughness element. 36. An aerodynamic or hydrodynamic wall surface configured to modify the interaction of a boundary layer of a fluid with the wall surface, comprising: at least one array of roughness elements disposed on and extending therefrom the surface, wherein the array of roughness elements are positioned in successive ridges comprised of adjoined roughness elements, wherein each ridge of roughness elements is positioned substantially transverse to the flow of fluid across the wall surface, wherein each ridge of roughness elements forms a substantially saw tooth pattern when viewed from a plane substantially transverse to the wall surface and substantially parallel to the flow of fluid across the wall surface, the saw tooth pattern having a selected wavelength, wherein each roughness element has a peripheral edge, wherein adjacent and aligned roughness elements in a ridge of roughness elements are connected at a medial portion of the respective peripheral edges of the roughness elements and define a channel between portions of the bases and the bottom portions of the peripheral edges of the adjacent and adjoined roughness elements, wherein the array of roughness elements defines a plurality of cavities, and wherein the thickness of the boundary layer is at least 20% of a cavity height of each cavity such that shear layer instabilities of cavity vortexes that form therein the plurality of cavities are reduced. 37. The wall surface of claim 36, wherein each formed cavity vortex has a Re in the range of between 100 and 20,000, relative to the cavity height, velocity of the fluid over the wall surface, and the kinematic viscosity of the fluid, such that the instability of the formed cavity vortexes are suppressed. 38. The wall surface of claim 36, wherein each channel extends longitudinally substantially co-axial to the flow of the fluid across the wall surface. 39. The wall surface of claim 38, wherein the peripheral edge of each roughness element 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, wherein a plurality of roughness elements within each ridge of roughness elements are positioned transverse to the flow of fluid across the surface such that a distance between the midpoints 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. 40. An aerodynamic or hydrodynamic wall surface configured to modify the interaction of a boundary layer of a fluid with the wall surface, comprising: at least one array of roughness elements disposed on and extending therefrom the surface, wherein each roughness element has a front, upstream surface and an opposing rear, downstream surface, wherein each roughness element has a substantially oval cross-sectional shape relative to a plane transverse to the flow of fluid over the wall surface, wherein a bottom portion of each roughness element is connected to the wall surface, wherein a peak longitudinal height of each roughness element is greater than a peak width of each roughness element, wherein a distance from the front surface to the rear surface in a medial portion of each roughness element is greater than the distance from the front surface to the rear surface in an upper portion and the bottom portion of each roughness element, wherein the array of roughness elements defines a plurality of cavities, and wherein the thickness of the boundary layer is such that shear layer instabilities of cavity vortexes that form therein the plurality of cavities are reduced.