A drag reduction structure wherein a first portion including a plurality of convex portions and concave portions, and a second portion are placed on a first surface; a height from a bottom portion of the concave portion to a top portion of the convex portion, of the first portion, is 10 ?m or more and 1000 ?m or less; a length of the first portion in a second direction is 30 mm or more; and a width of the first portion and a width of the second portion, in a first direction crossing the second direction, is 0.2 mm or more and 50 mm or less.

Various embodiments of an airfoil and machines with airfoils are disclosed. The airfoils include a thicker leading airfoil portion and a thinner trailing airfoil portion. In one embodiment, the leading airfoil portion is formed by bending a body of the airfoil back toward itself. In another embodiment, the leading airfoil portion has a solid geometry and includes two elliptic surfaces. To prevent detachment of airflow, the leading airfoil portion includes at least two arc portions or surfaces that act to direct the airflow down to the trailing airfoil portion in a manner that stabilizes vortexes that may form in the region of changing thickness.

A multilayer construction for an array of aerodynamic riblets incorporates a first layer composed of a material with protuberances, the first layer material having shape memory and a second layer composed of a material exhibiting a second characteristic with capability for adherence to a surface.

A technique for reducing erosion on the interior of a production component of a well system involves coating the interior of the production component with a series of ribs and grooves. The coating can be a non-metallic material in which the ribs and grooves are formed. The coating can also be applied as a series of ribs that are attached to the interior surface of the production component. The series of ribs can be made of alternating materials that have a different hardness causing the ribs to wear at different rates.

An object or a vehicle is disclosed that is configured for moving through a fluid or for relative movement of a fluid past the object, the fluid comprising air or water, the object or vehicle further comprising: a structure having a surface, wherein the surface is exposed to the fluid as the vehicle moves through the fluid; and the surface having a surface texture comprising a wave structure transverse to a principal direction of flow of the fluid over the surface, wherein the surface texture is configured to reduce skin-friction drag on the vehicle or object. A material is disclosed that is configured for use on a surface of a vehicle for the purpose of reducing skin-friction drag. A method is disclosed for reducing skin-friction drag on a vehicle, the method comprising forming a wavelike pattern on a surface of a structure.