Intrinsic sound, noise and instabilities directly or indirectly due to the shedding of cross-stream vortices caused when air or fluid moves over the trailing edge of a plate, blade, vane or the like are reduced by the formation of relatively steady-state streamwise vortices upstream of the terminal edge. The invention is applied to turbine and compressor blades, jet tube inlets and exits, heat-exchanger tubes and the like by placing or forming streamwise vortex-inducing generators within the boundary layer on the shedding item so that the induced streamwise vortices trail off of the trailing edge and suppress the formation of cross-stream disturbances. Through this process, noise disturbances which would otherwise amplify to high sound intensitites and/or large flow disturbances, high structural stresses and loss of efficiency through passage over successive shedding items are suppressed in their early stages of development.

Control of noise and instabilities in jet engines, compressors, turbines, heat exchangers and the like

An aircraft swept wing which provides pitch stability during stall conditions. In a swept wing aircraft which has leading edge flaps which in their deployed position forms a slot between the slot and the leading edge portion of a fixed main wing structure, the configuration of said leading edge portion is varied spanwise to vary the localized aerodynamic pressure spanwise along the wing. Increased bluntness of said leading edge portion, or increased slot-gap width, creates a stall condition on an inboard portion of the wing which approximates, at increasing angles of attack, the lift and pitching moment changes simultaneously experienced on outboard portions of the wing. As a result, adverse nose-up pitching moment under stall conditions is avoided, and improved pitch stability is achieved in swept wing aircraft, without compromising maximum lift capability.

Apparatus and method for aircraft wing stall control

A body (30) adapted to move downstream through a fluid has a downstream extending smooth surface (32) ter­minating at a blunt base. A plurality of adjacent U-shaped, downstream extending troughs (40) in the smooth surface (32) intersect the blunt base to form trough outlets (45). The troughs (40) are appropriately spaced apart, sized and configured to flow full over their entire length and cause fluid to flow into the space immediately behind the blunt base, thereby reducing base drag on the body (30).

Bodies with reduced base drag

Streamwise ridges on a lifting wing intercept local flow consisting of free stream and spanwise crossflow to create a pattern of vortices over the wing and aligned with the ridge axes; the vortices act as suction pumps collecting low energy boundary layer fluid, ingesting such fluid into the core of the vortices, transporting it in the streamwise direction, and discharging it into the wake. Fresh fluid from the outer, free stream flow replaces the spent fluid withdrawn by the vortex array. This produces a favorable pressure gradient that maintains laminarity, avoiding the onset of boundary layer transition leading to turbulence. The favorable pressure gradient also suppresses separation on the back side of the wing, where the pressure gradient is normally positive and adverse. The accelerations of fluid resulting from the ridges is an order of magnitude greater than the usual streamwise accelerations produced by wing shape and friction resulting in low effective Reynolds' number dominating the boundary layer and corresponding to laminar flow. Close spacing of the ridges maximizes the interception of local flow. Each ridge is asymmetric in cross-section with a gentle ramp on its windward side and a steep bluff on its lee side to generate a standing vortex between two consecutive ridges. A slight inclination of the ridge with respect to the free stream direction at least aft of the wing's maximum thickness taps the flow in the free stream direction to augment the acceleration produced by spanwise crossflow.

Laminar vortex pump system

An automobile includes a main front air screen generator having a curved wall member extending rearwardly and upwardly to a crest. A central deflector plate develops an air screen in front of the vehicle and a low pressure pocket behind the curved member. The surfaces of the automobile include minute wave-shaped flutes, each including a trough which extends upwardly and rearwardly to a relatively sharp crest and then breaks downwardly and forwardly into the next trough such that any impactive air moves over the surface with engagement only at the crest portions. A screen covers the flutes on the back surfaces and curved vances extending rearwardly and upwardly may optimize the pressure condition.

Scott C Rethorst

Papers

Vertically asymmetric diffuser system for reducing aircpaft induced drag