Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Radial flow devices
Patent
1985-02-07
1987-08-18
Garrett, Robert E.
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Radial flow devices
416200R, B64C 1116
Patent
active
046874160
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for reducing the flow resistance of wings, particularly airfoils and blades of turbomachines around which flow gases, such as air or the like, and to a device for performing the method.
When air or some other gaseous fluid flows around the wings of the aforementioned type, the problem exists that a flow can only be obtained with a limited resistance if in the vicinity of the wing profile vortex formations are avoided or at least minimized, because flow eddies considerably increase the flow resistance of the wing. In the case of airfoils the problem exists in that in the approach flow area of the profile, the laminar interface changes over from a laminar into a turbulent flow over the profile depth, so that in the rear area of the airfoil profile a vortex area is formed. In addition, at the edge of the airfoil pressure differences in the flow on the upper and lower surfaces of the airfoil lead to marginal vortexes, which slope downwards towards a vortex train. In order to limit the effects of these features, it has already been proposed to arrange special flaps on the leading and/or trailing edge of the wing and by means of which energy is supplied to the flow on the top of the profile by induction action. Although this energy supply displaces the separation point of the flow towards the trailing edge of the wing, it cannot eliminate it. A particular disadvantage of these flaps is that when they are extended the fineness ratio of the airfoil profile is in part considerably impaired. For preventing marginal vortexes it is also known to provide vertical auxiliary wings at the wing ends which, although reducing vortex formation, increase the flow resistance. In order to minimize the flow losses in the case of blades and which consists of the separation and turbulence losses, it is known to twist or warp the blades over their length, in order to prevent a breakaway of the flow from the blades and consequently turbulent vortex formation by an oblique incidence of the flow in the front area of the profile. In the rear area and at the free end portion of the blades, turbulence occurs in the same way as on the airfoil and the magnitude thereof is dependent inter alia on the flow velocity. It has therefore already been proposed to pivot the blades in the vicinity of the blade base in order to counteract breaking away of the flow by varying the angle of incidence. However, this requires high constructional, manufacturing and control expenditure and increases the failure property of a turbomachine equipped with such blades.
The object of the invention is to provide a device making it possible, without using special flaps, to influence the flow round profiles of wings, particularly airfoils and blades of turbomachines in such way that the separation point of the laminar wing length is displaced towards the trailing edge of the wing. According to the invention this object is achieved in that gas flowing in front of the leading wing edge is compressed and is expanded on the upper surface of the wing, so that through induction of the expanded gas, gas from the area of the lower surface of the wing is admixed and, simultaneously, the flow on the upper surface of the wing is increased and directed in such a way that the velocity of the gas flowing out at the trailing edge of the wing is identical over the wing length. The separation point of the flow is displaced towards the trailing edge of the wing and, in the direction of the edge of the wing, the pressure of the gas flowing over the upper surface of the wing is increased.
According to a further development of the invention, the device for obtaining the compression ratios sought on a wing according to the invention is characterized in that one or more blades are arranged on the top surface of the wing in the vicinity of its leading edge and are integrated into the profile of the root of the wing and are uniformly twisted over its length in such a way that
(a) the distance between the blade and the wing and optionally between the
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Garrett Robert E.
Kwon John
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