Pressure oscillations or acoustic loads over an open type cavity having a front face an upper edge of which constitutes a leading edge and having a rear face an upper edge of which constitutes a trailing edge are reduced by applying curvature to the rear face so as to present a convex curved surface internal to the cavity. In one embodiment, a cross-section through a longitudinal axis of the convex curved surface describes part of an ellipse.

A device is provided for controlling fluid flow over a window of a movable optical instrument housing. The device includes a generally annular body having an inner peripheral edge configured to correspond to a peripheral edge of the window of the housing and an outer peripheral edge, an arcuate outer surface disposed between the inner peripheral edge and the outer peripheral edge, and a reduced width portion between the inner peripheral edge and the outer peripheral edge. The reduced width portion is configured to lower elevation torque. Other embodiments of the device and methods for controlling fluid flow are further disclosed.

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.

A layer system having a metallic substrate, in particular made of a >=9% by weight chromium steel, in particular with roughness of the substrate <=2 ?m and optionally an intervening chromium layer directly on the substrate, in particular made of Cr/CrN, an underlayer or middle layer of AlCr, and an outer layer, in particular outermost layer, of AlCrO, where the AlCr and AlCrO layers in particular are PVD coatings wherein a shark skin effect is achieved with a simple geometric arrangement, and can be used particularly for compressor blades.

An article that includes a vortex-generator device may include various features. For example, the article may include a material layer and one or more elongate members coupled to the material layer. In addition, the one or more elongate members interconnect two or more vortex generators.

A microstructured surface with microfeatures formed thereon and defining spaces between the microfeatures includes least one electrode of an electrode pair in the spaces, wherein electrodes of the pair are electrically connected to one another. The at least one electrode located in the space is configured to generate a gas in between the microfeatures when an electrolyte solution penetrates into the microfeatures. Importantly, the electrodes are not connected to any external power source. Because the microstructured surface is self-powered in replenishing the gas lost in a submerged condition, no additional provision to supply energy or regulate the replenishment is necessary for implementation and use.

Airfoil and hydrofoils systems with structures having a surface texture defined by fractal geometries are described. Raised portions or fractal bumps can be included on the surfaces, forming a surface texture. The surface textures can be defined by two-dimensional fractal shapes, partial two-dimensional fractal shapes, non-contiguous fractal shapes, three-dimensional fractal objects, and partial three-dimensional fractal objects. The surfaces can include indents having fractal geometries. The indents can have varying depths and can be bordered by other indents, or bumps, or smooth portions of the airfoil or hydrofoil structure. The fractal surface textures can reduce vortices inherent from airfoil and hydrofoil structures. The roughness and distribution of the fractal surface textures reduce the vortices, improving laminar flow characteristics and at the same time reducing drag. The systems are passive and do not require applied power.

This relates to the field of aerohydrodynamics and can be used on wings and control surfaces of aircraft, controlled spoilers of sports cars, all-movable masts and sails of sailing yachts and sailboards, as well as on blades and vanes of various bladed machines. An aerohydrodynamic surface includes an array of vortex generators and a main part. The main part comprises two sides mating with each other to form a leading and a trailing edges. The array of vortex generators includes elevations with crescent-shaped working edges located near the leading edge. The elevations and the working edges are configured to generate counter-rotating vortex structures. An array of vortex generators and a method of mounting the same onto the aerohydrodynamic surface are also described. The invention makes it possible to improve the properties of the aerohydrodynamic surfaces at high angles of attack.

A layout for asymmetric trip strips including a flow passage having a lower wall and an upper wall opposite the lower wall, each of the lower wall and the upper wall including an inner surface, the flow passage having a passage inlet and a length L and a diameter d; multiple skewed trip strips extending from at least one inner surface of the lower wall or the upper wall; and at least one periodic reflection of the skewed trip strips along the flow passage downstream of the passage inlet at a frequency with a length-to-diameter ratio of L/d20.

A device is provided for controlling fluid flow over a window of a movable optical instrument housing. The device includes a generally annular body having an inner peripheral edge configured to correspond to a peripheral edge of the window of the housing and an outer peripheral edge, an arcuate outer surface disposed between the inner peripheral edge and the outer peripheral edge, and a reduced width portion between the inner peripheral edge and the outer peripheral edge. The reduced width portion is configured to lower elevation torque. Other embodiments of the device and methods for controlling fluid flow are further disclosed.