Aeronautics and astronautics – Aircraft structure – Details
Patent
1995-10-31
1998-04-28
Kashnikow, Andres
Aeronautics and astronautics
Aircraft structure
Details
244130, 244207, 244208, B64C 138
Patent
active
057434930
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to boundary layer control in aerodynamic low drag structures and is particularly although not exclusively concerned with the control of laminar flow of air in a boundary layer adjacent an outer skin surface of an aero-engine nacelle.
It is well known to provide control over a boundary layer adjacent an aerodynamic surface exposed to air flow over it by injecting air into the boundary layer or by withdrawing air from it. In boundary layer control by injection of air, high speed air is blown into the boundary layer to prevent or control separation, that is to say, detachment of the flow from the aerodynamic surface with which it has been in contact. In boundary layer control by withdrawal of air from the boundary layer, separation is prevented or controlled by removing the layer which would otherwise separate. In addition to preventing or controlling separation, withdrawal of air has also been used to prevent or control boundary layer transition, that is to say, the change from laminar to turbulent flow in the boundary layer and is of particular interest in maintaining laminar flow over surfaces of structures required to have low drag characteristics.
Aero-engine nacelles are routinely designed to provide outer skin profiles having low drag characteristics. It has been found that the aerodynamic efficiency of the nacelle is seriously impaired by transitions from laminar flow to turbulent flow in the boundary layer adjacent the outer skin. The maintenance of laminar flow significantly improves the specific fuel consumption (SFC) of the engine and in consequence efforts are constantly being made to produce and sustain laminar flow.
It has been proposed to encourage laminar flow over a nacelle outer skin by withdrawing air through the nacelle skin by the use of suction pumps and exhausting the withdrawn air into turbulent air flow downstream of the nacelle. Such proposals have however made use of electrical power, bleed air from the engine compressor or ejectors which also make use of engine compressor bleed air. There is however the disadvantage that while the specific fuel consumption (SFC) of the engine is improved by the introduction and maintenance of laminar flow the energy employed to drive the suction pumps and to create the laminar flow has the opposite effect and reduces the specific fuel consumption of the engine.
It is an object of the present invention to provide a means by which laminar airflow over a nacelle outer skin can be improved by withdrawing air through the nacelle skin but which does not suffer or does not suffer to the same extent from the above-mentioned disadvantage.
According to a first aspect of the present invention, there is provided an aerodynamic low drag structure which has a skin and which in movement of the structure relative to a surrounding gaseous fluid medium produces at a flow control region of the skin laminar flow of the gaseous fluid in a boundary layer adjacent the skin, characterised by the provision of a first inlet opening in the skin in the flow control region, first gaseous fluid conveying means within the structure by which fluid withdrawn from the boundary layer into the first inlet opening is conveyed along a first fluid flow path within the structure for discharge from the structure at a discharge opening downstream of the first inlet opening, a second inlet opening in the skin of the structure in a gaseous fluid ram region of the skin in which the skin is subjected to gaseous fluid of the surrounding medium at a predetermined ramming pressure, second gaseous fluid conveying means within the structure in which gaseous fluid under ramming pressure is conveyed from the second inlet opening in the skin along a second fluid flow path within the structure to the discharge opening or a further discharge opening and impelling means so positioned and arranged that the flow of fluid under ramming pressure in the second fluid flow path causes the fluid in the first fluid flow path to be impelled along the first fluid flow path from the fi
REFERENCES:
patent: 2374607 (1945-04-01), McCollum
patent: 2433586 (1947-12-01), Webberking
patent: 2646945 (1953-07-01), Perry
patent: 2833492 (1958-05-01), Fowler
patent: 4607657 (1986-08-01), Hirschkron
patent: 4641799 (1987-02-01), Quast et al.
Dinh Tien
Kashnikow Andres
Short Brothers PLC
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