Free-standing turbine blade

Abstract

There is described a blade for a turbomachine, such as a steam turbine. The blade has a blade tip, which is curved in relation to the blade airfoil profile. The curvature has the shape of a winglet, which is known from aircraft construction.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority of European Patent Office application No. 07002465.8 EP filed Feb. 5, 2007, which is incorporated by reference herein in its entirety.FIELD OF INVENTION[0002]The invention relates to a blade for a turbomachine, wherein the blade is formed along a radial direction and has a blade tip and also a blade profile with a pressure side and a suction side.BACKGROUND OF INVENTION[0003]Free standing lowpressure blades are used in turbomachines, such as in steam turbines, primarily in the low-pressure region. For constructional reasons, such turbomachines have a comparatively large radial gap between the blade tip and the casing. So that losses, however, do not become too great, it is known to arrange abrasive coatings on the blade tip or on the casing which lies opposite the blade tip. With contact between the blade tip and the casing, only the abrasive coating is slightly worn away, as a result of which a comparativ...

AI Technical Summary

Benefits of technology

[0007]It is an object of the invention to disclose a turbine blade for a turbomachine, which can be used in a turbomachine and during operation leads to low gap losses.

[0010]By this measure, the driving pressure difference across the blade tip is reduced. A further effect is that the radial clearance between the blade tip and the casing is reduced, and consequently the gap loss becomes less. The efficiency of such a turbomachine is ultimately improved.

[0011]Furthermore, the aerodynamic conditions in the region of the blade tip can be better controlled, since aerodynamic shocks of the flow around the profile are shielded against interaction with the casing. As a result of this, shock reflexes are reduced.

[0015]So, it is advantageous if the blade tip, as seen in the radial direction in the direction of the blade tip, is formed in a manner in which it is first curved towards the suction side and then curved towards the pressure side.

[0016]As a result of this, the centrifugal force which acts upon the blade tip is minimized, as it were, in an optimum manner because the centrifugal force acts on the one hand upon one side (suction side) of the extension direction of the blade and on the other hand upon the other side (pressure side) of the extension direction of the blade.

Problems solved by technology

In low pressure steam turbines, these gap jets cause pulsing flows in the diffuser, which can lead to unwanted humming of the diffuser.

However, such blades with shrouds have mechanical disadvantages because the shrouds represent comparatively large additional masses which lead to an unwanted mechanical loading of the blades.

A further disadvantage which is brought about by the shrouds arises as a result of interconnecting the blades via the shrouds.

Such connections can lead to additional vibrational and resonance modes of the blade ring which is connected in this way.

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