Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Having wear liner – sheathing or insert
Reexamination Certificate
2001-12-17
2003-12-02
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Having wear liner, sheathing or insert
C416S22900R
Reexamination Certificate
active
06655921
ABSTRACT:
The present disclosure relates to the subject matter disclosed in German applications No. 100 65 192.5 of Dec. 18, 2000 and No. 101 10 102.3 of Mar. 2, 2001, which are incorporated herein by reference in their entirety and for all purposes.
BACKGROUND OF THE INVENTION
The invention relates to a rotor blade of hybrid design comprising a vane and a blade root, the vane comprising a first vane portion made of a metallic material and a second vane portion made of a lightweight material.
Such a rotor blade is described in DE 197 51 129 C1. Herein the vane is held in a slot formed on a metallic vane portion.
A rotor blade is known from EP 0 764 763 A1, wherein a second segment made of a composite material is placed in a first segment made of a metallic material.
In the article “Ein starker Verdichter” (“A strong compressor”) in the DLR-Nachrichten (DLR News) of June 2000, pages 54-57, a hybrid blade comprising a part made from a carbon fiber composite material is described.
Further rotor blades of hybrid design are known, for example, from DE 1 628 355, GB 2 264 755 A, U.S. Pat. No. 3 883 267, DE 195 35 713 A1, DE 26 31 856 C2 or DE 2 042 665.
Starting therefrom, the object underlying the invention is to create a rotor blade of hybrid design having, on the one hand, a low mass, and, on the other hand, a high bearing capacity with respect to loads.
SUMMARY OF THE INVENTION
This object is accomplished with the rotor blade mentioned at the outset, in accordance with the invention, in that a rear edge of the rotor blade is formed on the second vane portion, and in that the second vane portion is joined to the first vane portion in a single-section-type manner.
With the hybrid construction, various materials with different physical properties are combined with one another to achieve an optimum design for a rotor blade. A rear edge of the rotor blade has essentially only an aerodynamic function and can, therefore, be formed on the second vane portion made of the lightweight material. The weight of the rotor blade according to the invention can be minimized by such a “light” rear edge.
When joining two parts made of different materials, mechanical stresses are caused, in principle, in transition areas, on the one hand, by the manufacture, and, on the other hand, by loads during use, which are due to different material behavior and to different physical and chemical material properties, such as, for example, thermal expansion, shrinkage processes during polymerization and curing (hardening) and different rigidities and different transverse contraction behavior. Hydrostatic stresses between the first vane portion and the second vane portion are strongly reduced by the second vane portion being joined to the first vane portion in a single-section-type manner. Such stresses occur when one part is at least partially enclosed and/or embraced by a second part, and three-dimensional constraints are caused thereby. These occur, in particular, when two parts embrace one another in a clamp-like fashion. Owing to the single-section-type joint according to the invention, deviatoric stresses preferably occur during the manufacture, and, in contrast to hydrostatic stresses, these can already be relaxed by flow processes in the course of manufacture of the single-section-type joint, with the second vane portion joined to the first vane portion in a tapered manner with a gradual increase in the width of one portion and a corresponding gradual decrease in the width of the other portion. Fewer material problems thus occur with the rotor blade according to the invention, as an homogeneous transition is achieved between the first vane portion and the second vane portion. At the same time, however, mass can be saved, which, in turn, results in a reduction of the load on the blade root.
The combination of a light rear edge with a single-section-type joint thus results in the mass of the rotor blade being reduced and in material problems, such as occur with the hybrid design, being at least diminished.
During operation, a rotor blade may be subjected to high temperatures, which results in a corresponding thermal expansion of the material of the rotor blade. With three-dimensional constraints, this can lead to the occurrence of stresses which limit the stability of the rotor blade under load. The danger of breakage caused by thermal stresses is strongly reduced by the single-section-type joint according to the invention, with which three-dimensional constraints are essentially avoided, because these stresses are easier to reduce or do not occur or not to the same extent as when three-dimensional constraints prevail.
In accordance with the invention, a rotor blade with a high bearing capacity with respect to dynamic and quasistatic loads and also with respect to impact loads such as bird strikes and with a relatively low mass can then be created.
It is of advantage for the second vane portion to be joined to the first vane portion in a tapered manner with a gradual increase in the width of one portion and a corresponding gradual decrease in the width of the other portion, so as to avoid material problems in the transition area between the first vane portion and the second vane portion.
It is of particular advantage for a front edge of the rotor blade to be formed on the first vane portion (“heavy front edge”). A stagnation point of the air stream flowing around the rotor blade lies at the front edge. The latter is, therefore, under heavy load, and the metallic material of the first vane portion ensures good protection against erosion. Moreover, the danger of bird impact is also considerably higher in the area of the front edge of the rotor blade. The metallic material of the first vane portion can absorb the energy of the bird impact irreversibly by plastic deformation without loss of the vane itself. This means that the operation of an engine equipped with rotor blades according to the invention is still possible in spite of bird impact.
The first vane portion advantageously protrudes in a front portion thereof beyond the second vane portion. An increased resistance to erosion with respect to the front edge is thereby achieved, and, on the other hand, the total mass of the vane can be minimized. To this end, a front edge of the rotor blade is expediently formed in the front portion.
It is also particularly expedient for the second vane portion to protrude in a rear portion thereof beyond the first vane portion. In this way, the rear edge can be formed on the second vane portion, and the mass of the vane can thereby be further reduced and the load on the blade root thus decreased. The rear portion is designed so that it has essentially only an aerodynamic function, and its force load, in particular, with respect to centrifugal forces, buoyancy forces, erosion and impact such as by bird strikes is low or has only a slight probability of occurrence. In particular, the rear edge of the rotor blade is formed in the rear portion.
In order to form a single-section-type joint surface between the vane portions, with the vane portions joined together in a tapered manner with a gradual increase in the width of one portion and a corresponding gradual decrease in the width of the other portion, it is particularly expedient for the second vane portion to be arranged on the first vane portion. In addition, the rotor blade according to the invention can thereby be manufactured in a simple way, as the first vane portion can be manufactured separately from the second vane portion.
It is of advantage for the first vane portion to form a concave side of the rotor blade at a front edge of the rotor blade. Furthermore, it is expedient for the first vane portion to form a convex side of the rotor blade at a front edge of the rotor blade. The front edge is thus made of the metallic material and, in particular, a good resistance to erosion and impact is thus achieved.
It is also expedient for the second vane portion to form a concave side of the rotor blade at a rear edge of the rotor blade. In addition, the second vane portion forms a c
Deutsches Zentrum fuer Luft -und Raumfahrt e.V.
Lipsitz Barry R.
McAllister Douglas M.
McCoy Kimya N
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