Fluid reaction surfaces (i.e. – impellers) – Projecting blade axis offset from rotation axis
Patent
1994-06-10
1995-10-31
Look, Edward K.
Fluid reaction surfaces (i.e., impellers)
Projecting blade axis offset from rotation axis
416204R, 416205, 416210R, 416219A, F04D 2938
Patent
active
054624118
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention has as its object an improved device for connecting blades to a hub in propellers of fans, aircraft and other applications, with variable fitting whether in the stopped position or in motion.
2. Description of the Related Art
In the application for European Serial No. 90810598.4 of the same Ceute applicant, published on Feb. 20, 1991 with publication No. 0 413 663 A2 with Argentine priority of Aug. 14, 1989, a device is claimed in which the connection of each blade to the hub took place by means of a screw placed outside the contour of the blade.
The screw acted as a pivot for the variation of the fitting of each blade, by ensuring the mechanical blocking of the blade itself to the hub, at the desired fitting.
In the Italian patent application Serial No. 91A 003500 in the name of Elica s.r.l., filed on Dec. 30, 1991, there is a blade-hub connection that falls within the above-mentioned previous European patent application, inasmuch as the attachment of the blades to the hub, although realized in a different manner, has the longitudinal axis of the screw located outside the contour of each blade (see for example FIGS. 13 and 14 of that patent application).
Both in the device according to the EPO patent application, and in the Italian patent application just cited, the blade was practically not disturbed structurally at the base by maintaining the full resisting section in the areas of maximum bending moment.
The disadvantage of the "Ceute" device was that it had to have hubs large in diameter since each blade, for at least 50% of the span had to be superimposed on the hub.
This arrangement did not constitute a drawback for fans of large diameter, made up of blades characterized by significant slenderness (by slenderness is meant the ratio: radius of the blade/span of the blade): the large diameter hub serves to reduce the length of the blade and thus the stresses, and to create a shield to prevent the reverse flow in the area of the hub.
Obviously, this effect can be obtained in a much less costly way by a simple sheet metal, aluminum or plastic disc.
On the other hand, with small diameter fans, the "Ceute" device would compromise the performance of the fan, since it necessitated a hub of excessive diameter with the resulting necessity of fairing upstream from the hub.
The "Elica" device, in practice, although it reduces costs with respect to the solution just examined inasmuch as the cost of the hub decreases significantly, presents the drawback, for small fans, of exhibiting the bases of the blades that are altered from the aerodynamic standpoint.
The presence of support 15 in FIG. 14 in the "Elica" device significantly alters the aerodynamic field at the base.
Both the "Ceute" and the "Elica" devices can find their field of application for axial fans characterized by a ratio of radial extension of the blade outside the support/radius of the blade itself close to the unit.
This ratio is used for the reasons stated above and especially when the fans are made to operate at a high tip speed.
In this case for equal yield, few blades are required, in addition to the significant slenderness, with the high tip speed compensating for the small surface of the blades.
In the last 10 to 20 years, on the other hand, in countries with a high population density, industrial and civilian plants are required to observe ever stricter norms relating to noise.
For this reason, with equal diameter and equal yield, due to the tip speed of the propellers, the major cause of noise must be significantly reduced and the surface area of the blades must increase at least by the square of the ratio: ##EQU1## in which 60 and 45 are the tip speeds of the 1970's and 1990's devices in meters/second. Furthermore by increasing the surface area of the blade or to say it more precisely the solidity (understood as the ratio between the surface of the blades and the surface of the fan disc), aerodynamic interference is manifested between one blade and another, and thu
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patent: 3480373 (1969-11-01), Talbot
patent: 4396352 (1983-08-01), Pearce
Ceute S.A.
Look Edward K.
Verdier Christopher
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