Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Tined or irregular periphery
Reexamination Certificate
1998-12-24
2001-10-16
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Tined or irregular periphery
C416S243000
Reexamination Certificate
active
06302652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates to the field of fluid dynamics and more particularly to the field of propellers or windmills.
2. Description of Related Art
Propellers are able to propel objects by exploiting the principle of conservation of total linear momentum. Propeller blades accelerate fluid so that the speed of the fluid entering the propeller is lower than the speed of the fluid exiting. The propeller, and whatever is attached thereto, must therefore move in the forward direction to ensure the conservation of total linear momentum. Because of this difference in fluid speeds, the concentration of streamlines at the rear of the propeller blades is higher than at the front. Or, what is the same, A
1
>A
2
, where A
1
and A
2
are the cross-sectional areas, perpendicular to the streamlines, of a tube of flow fore and aft of the propeller. The larger the ratio A
1
/A
2
, the more energy can be put into the airstream.
In conventional blades, however, blade tip vortices and other inefficiencies are introduced as the fluid near the blade tips escapes from the rear to the front. These tip losses result in a diminution of A
1
/A
2
. I.e., these tip losses reduce the concentration of the streamlines at the rear of the propeller and increase the concentration at the front, leading to undesirable loss of thrust and efficiency.
Another problem shared by conventional propellers is that the optimum blade size needed to produce the required thrust is often too large to allow the propeller to turn. For example, the size of a propeller producing the required thrust for an airplane may be too large to clear the tarmac while rotating. Or, in another example, the optimum blade size producing the desired thrust for a boat may be such as to impede proper functioning of a boat propeller in shallow water. While truncating the blades would solve the aforementioned problem, this truncation may result in more tip loss and less efficiency. Also, as blade diameter increases, a gearbox ratio also increases, adding weight and reducing efficiency.
SUMMARY OF THE INVENTION
The present invention addresses the aforementioned problems by introducing blades which, unlike the conventional shape, are not planar. Rather, the tips have a directional component that points in the direction of airflow. By shaping the blade tips into a curve having a continuous tangent, tip vortices are reduced and, with the appropriate profiles and pitch angles, more efficient operation can result. Curving the blades also recaptures the lost blade area that truncation loses.
The blade tips can be bent so as to point in approximately the same direction as the axis of rotation. By curving the blades in an approximately semi-elliptical shape in this fashion, air may be drawn from outside the semi-ellipsoidal envelope (open end facing downstream for propellers) by the blade tips to accelerate the airflow already established by the portions of the blade closer to the hub. By employing semi-elliptically shaped blades, then, the concentration of streamlines in front of the propeller is decreased while the concentration at the back is increased. The ratio A
1
/A
2
is therefore augmented. These modifications result in a more efficient and ideal propeller.
The above considerations also apply to windmills. Here, however, it is desirable to harness the wind's energy to turn the blades. I.e., in contrast to propellers, windmills are designed to reduce the wind speed as the air traverses the blades. Curving the blades in a semi-ellipsoidal manner as described above, while making the blades' angles of attack have the opposite sign as those of a propeller, results in more efficacious operation. The curved shape serves as a virtual venturi with the windmill at the neck of this venturi.
Adopting a curved propeller shape described above may permit the attainment of the same thrust as a conventionally shaped propeller, but with less blade material. This feature not only permits more compact operation, but also reduces costs in the manufacturing process. Moreover, because the propeller or windmill of the present invention would be expected to have a smaller moment of inertia, the same torque exerted on the blades would produce a greater angular acceleration than in conventional models.
REFERENCES:
patent: 3580210 (1971-05-01), Svensen
patent: 3768922 (1973-10-01), Dixon
patent: 3989406 (1976-11-01), Bliss
patent: 4304524 (1981-12-01), Coxon
patent: 4359311 (1982-11-01), Benesh
patent: 4488399 (1984-12-01), Robey et al.
patent: 4838757 (1989-06-01), Benesh
patent: 410129590 (1998-05-01), None
Cavallo, Alfred J.; Hock, Susan M.; Smith, Don R.; “Wind Energy: Technology and Economics”, Chapter 3 in Renewable Energy: Sources for Fuels and Electricity, 1993, NY, Island Press, pp. 121-135.*
Bristish Patent application No. 2316980, Nov. 1998.*
Streeter, Victor L. and Wylie, E. Benjamin, Fluid Dynamics, 8thEdition, McGraw-Hill, NY © 1985, pp. 116-126, 164-172.
General Dynamics Government Systems Corporation
Jenner & Block LLC
Look Edward K.
Nguyen Ninh
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