Process for forming a surface for contact with a flowing fluid a

Details Process for forming a surface for contact with a flowing fluid a Process for forming a surface for contact with a flowing fluid a

1998-08-31

2000-07-25

Poon, Peter M.

Aeronautics and astronautics

Aircraft sustentation

Sustaining airfoils

244198, 244204, B64C 2110

Patent

active

060927666

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a method used for forming a solid surface for contact with a flowing medium. The invention also relates to a body having surface areas formed in accordance with the method of the invention. Such a body can be an airfoil, propeller, fan blade, turbine blade or stirrer. It can also be a body wholly or partly enveloping the flow, such as, e.g., a diffuser.


BACKGROUND OF THE INVENTION

It is known that laminar flows at a local Reynolds number lower than approximately 200,000 and with a positive pressure gradient (pressure rising in the flow direction) do not engage or stay near a surface but instead separate therefrom.
For this reason, the classic wing profile with a smooth or rough surface is consequently only usable above a minimum Reynolds number. For a Reynolds number below this minimum, the laminar boundary layer is separated from the solid surface on the suction side of the wing profile in the vicinity of the profile leading edge. This fact not only limits the use of airfoils, propellers, etc., but also the stirring action of stirrers, with which, in relatively viscous media, laminar flows are produced. This fact also limits the pressure recovery in diffusers.


SUMMARY OF THE INVENTION

An object of the invention is to provide a method by which the surfaces for the contact with a flowing fluid are so constructed that a laminar fluid flow is less easily separated from the surface, i.e., the laminar flow, also in the case of-local Reynolds numbers of less than 200,000 and positive pressure gradients, stays near the surface. A further object of the invention is to provide bodies which have surface areas formed in accordance with the method and which can consequently be used more advantageously at lower Reynolds numbers than the corresponding, known bodies.
This object is achieved by the method for forming surfaces for contact with flowing media and by the body with the correspondingly formed surface areas, wherein the surface for contact with flowing fluid is provided with a plurality of grooves which are inclined to the flow direction and have an upstream-directed, closed entrance and a downstream-directed, open exit. The orientation of the grooves relative to the flow direction, as well as their lengths, widths, depths and mutual spacing are to be adapted to the flow conditions, as will be described hereinafter.
The grooves are made in the surface or the surface is lined with a suitably structured lining.
It has been found that a laminar flow, when flowing over a surface formed in accordance with the invention, produces in the grooves a vacuum as a result of which the flow better engages with the surface. In addition, the fluid at least partly does not directly flow along the solid surface but instead flows over the fluid located in the grooves, which does not flow or flows more slowly and/or in a differently directed manner. As a result, the main flow becomes a free jet, at least over the grooves and in its boundary area shear forces occur which, more particularly in the case of low Reynolds numbers, are much lower than the frictional forces with a solid surface. As a result, the friction loss of a flow over the grooved surface of the inventive body is much lower than the corresponding loss of the same flow over a smooth or rough surface.
Surfaces constructed in accordance with the invention are advantageously used on the suction sides of airfoils in the vicinity of the profile leading edges, particularly in the area of control flaps. Axial fans with surfaces formed in accordance with the invention are usable with lower Reynolds numbers than hitherto, i.e., in areas where up to now redial fans or volumetric pump designs have been necessary. Small flight bodies, for which up to now relatively large wings with long chord lengths (profile depth) had to be used, can be more advantageously constructed with the inventively formed surface areas. The surfaces of entrance areas of diffusers can also be constructed according to the invention, so that much better

REFERENCES:
patent: 3584812 (1971-06-01), Brenman
patent: 3741285 (1973-06-01), Kuethe
patent: 4619423 (1986-10-01), Holmes et al.
patent: 4736912 (1988-04-01), Loebert
patent: 4750693 (1988-06-01), Lobert et al.
patent: 4753401 (1988-06-01), Bechert
Lin, J.C. et al, "Control of Turbulent Separated Flow Over a Rearward-Facing Ramp Using Longitudinal Grooves", Journal of Aircraft, vol. 27, No. 3, Mar. 1990, Washington, D.C., pp. 283-285.

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