Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Concave surface
Utility Patent
1998-12-14
2001-01-02
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Concave surface
C416S242000, C416SDIG002
Utility Patent
active
06168384
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of fluid dynamics. In particular, the invention pertains to aircraft and stationary fluid propellers.
The aerodynamic principle utilized in propellers is the effect of the dynamic pressure of the fluid to be propelled on the propeller blade. The resultant dynamic pressure is the sum of all partial pressures acting on the various surfaces of the blades. These effects are similar to the principles that are applicable in heavier-than-air craft which are lifted in air by the dynamic pressures acting on the craft as it is being propelled through the air. The dynamic pressure is proportional to the relative speed between the air and the propeller blade. Air resistance acting on poor aerodynamic shapes translates into drag, which is defined as the force counteracting the forward thrust force or torque of the propeller blade. A certain amount of drag cannot be avoided. However, the drag force can be minimized by the proper design of the shape of the blades and its maximization in terms of the useful translational speeds. The object is to minimize drag resistance and to maximize thrust force, i.e., to optimize the thrust-to-drag ratio.
The principles described herein are equally applicable to thrust propellers that are used to propel vehicles relative to the atmospheric air and pump propellers that are stationary relative to the ground and that are used to pump a flow of air (or other fluid).
Low speed, low power propellers are relatively simple. The thrust is obtained by a vertical force component acting perpendicularly to a movement of the blades. A thin plate with a narrow attack surface and a slight backward curve (camber) usually provides a sufficient amount of thrust. In other words, the pitch angle of the forward-most portion of the plate is approximately zero relative to the plane defined by the propeller sweep and the blade has a backward curve by a few degrees. With the relatively low speeds of the simple pump propellers, the slightly curved shape of the blade is generally acceptable. As the blade speed is increased, however, the thrust-to-drag ratio very quickly deteriorates. The drag is thereby caused by the turbulent flow, i.e., the vortices or eddies, at the trailing edge of the blade.
Propeller inefficiency is also affected by micro-friction between the exposed surfaces and the innermost layer (flow sheet) of the fluid impinging and being deflected by the surfaces. This invention, however, is primarily concerned with improving the macro-structure and the thrust-to-drag ratio of aircraft and pump propeller blades.
Similarly to aircraft wing design, where most of the lift on a wing is due to the vacuum effect above the wing (the negative pressure compensates for the fluid compression forward of and below the wing), the “shaded” surface of the propeller blade is important as well. The typical ratio in wings is that approximately two-thirds of the lift originates from the upper vacuum effect and one-third is due to the compression below the wing. This recognition, in the early days of wing design, resulted in the development of the airfoil. The airfoil shape at first glance appears counter-intuitive. The airfoil has a thickened forward section which tapers to a very thin tip structure at the trailing edge. Nevertheless, the basic airfoil shape was also adopted for propeller blades.
As noted, the principles concerning vortice creation and drag in wing designs are similarly applicable to propellers and rotor blades. Furthermore, the principles concerning aircraft propellers are also extendible to watercraft. There, the eddie formation principles applicable to the relatively thin fluid air find their equivalents in the denser fluid water with the formation of eddie current vortices, cavitation, and super-cavitation.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a novel propeller blade configuration, which further minimizes the above-mentioned disadvantages of the heretofore-known devices of this general type and which proposes a novel principle in propeller blade design that maximizes the thrust-to-drag ratio of propeller blades and the corresponding efficiency of propulsion propellers and stationary pump propellers.
With the foregoing and other objects in view there is provided, in accordance with the invention, a propeller configuration, comprising:
a rotatable hub defining an axis of rotation;
at least two blade structures attached to the hub substantially perpendicular to the axis of rotation;
each of the blade-structures having a leading edge, a trailing edge, a forward surface extending from the leading edge to the trailing edge, and a rear surface extending from the leading edge to the trailing edge;
the forward surface and the rear surface at the leading edge extending substantially parallel to and offset from the forward surface and the rear surface at the trailing edge.
The term propeller, herein, refers to propulsion propellers (aircraft, watercraft) as well as to stationary propellers used in high-power fans (wind tunnels, high velocity fluid pumps) and stationary turbines.
In accordance with an added feature of the invention, the forward surface and the rear surface are defined by a function y=cos x, where, 0≦x≦&pgr; in radians, x being approximately equal to zero at the leading edge and x being approximately equal to &pgr; at the trailing edge.
In accordance with an additional feature of the invention, the forward surface is defined by a function y=(cos x)+(sin (x/z)) and the rear surface is defined by a function y=(cos x)−(sin (x/z)), where 0≦x≦&pgr; in radians, and z>&pgr;, x being approximately equal to zero at the leading edge and approximately equal to &pgr; at the trailing edge.
In accordance with a further feature of the invention, z is a constant, or z is a function of x and has a maximum value smaller than a maximum value of x.
In accordance with again an added feature of the invention, the forward surface and the rear surface are defined by a function y=a cos x, where 0≦x≦&pgr; in radians, x being approximately equal to zero at the leading edge and x being approximately equal to &pgr; at the trailing edge, and a is a real number.
The term a may be constant, or it may be a function of x and have a maximum value smaller than a maximum value of x.
In accordance with again another feature of the invention, the forward surface and the rear surface are defined by a tangent function.
In accordance with again a further feature of the invention, the offset between the leading edge and the trailing edge increases with a distance from said.
In accordance with a concomitant feature of the invention, the forward surface and the rear surface are defined by a function y=d cos x, where 0≦x≦&pgr; in radians, x being approximately equal to zero at the leading edge and approximately equal to &pgr; at the trailing edge, and wherein d is proportional to the distance from the hub at which the blade structure is attached and assumes a maximum of no more than 1.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a propeller configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 2638171 (1953-05-01), Foss
patent: 3128939 (1964-04-01), Szydlowski
patent: 3174681 (1965-03-01), Monroe
patent: 4124329 (1978-11-01), Romanov et al.
patent: 5161953 (1992-11-01), Burtis
patent: 5575624
Greenberg Laurence A.
Lerner Herbert L.
Look Edward K.
McAleenan James M
Stemer Werner H.
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