Turbomachine Blade Cascade Torsional Stiffness Design
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Solution Overview
Problem
Existing blade cascades in turbomachines face instability and fatigue failure due to loss of shroud clamping, particularly in titanium-aluminum alloy blades, as they become aeroelastically unstable and wobble, leading to dynamic and flow-related disadvantages.
Innovation Solution
A blade cascade design where first blades are made stiffer torsionally than second blades, with shrouds of different extensions in the circumferential and axial directions, creating distinct natural frequencies and mass moments of inertia to enhance torsional stiffness and stability, while maintaining a homogeneous shroud surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radial wall thicknesses of shrouds are varied greatly to represent frequency differences, then natural frequencies of adjacent blade arrangements differ more, but the lateral surface of the shroud compound varies greatly in the radial direction causing dynamic and flow-related disadvantages
Solution Approach 1:
The patent applies local quality by varying the circumferential extension of shrouds in specific blade arrangements rather than uniformly varying radial wall thicknesses. Different blade arrangements have shrouds with different circumferential extensions, creating local differences in mass moment of inertia and natural frequencies without affecting the overall radial surface homogeneity of the shroud compound.
2Reliability
If radial wall thicknesses of shrouds are increased to influence mass moment of inertia, then natural torsional frequencies may be affected, but the influence on mass moment of inertia is only slight
Solution Approach 1:
The patent changes the parameter of circumferential extension of shrouds rather than radial wall thickness. By extending shrouds circumferentially, the mass moment of inertia about the radial direction is significantly increased, thereby affecting natural torsional frequencies more effectively than radial thickness variations.
3Stability of the object's composition
If shrouds of adjacent blade arrangements are made to contact in a clamped manner to increase stability, then blade wobble is prevented, but the system becomes sensitive to loss of clamping leading to aeroelastic instability
Solution Approach 1:
The patent segments the blade cascade into different blade arrangements with distinct shroud characteristics (different circumferential extensions). This segmentation creates different mass moments of inertia and natural frequencies for adjacent blade arrangements, reducing the risk of synchronized aeroelastic instability while maintaining individual blade stability through shroud clamping.
4Ease of manufacture
If all blade arrangements have identical shroud extensions to maintain manufacturing simplicity, then manufacturing is easier, but all blades have similar natural frequencies increasing fatigue failure risk
Solution Approach 1:
The patent introduces asymmetry by designing different blade arrangements with different shroud circumferential extensions. This asymmetric design creates a distribution of natural frequencies across the blade cascade, preventing resonant coupling and reducing fatigue failure risk, while still maintaining manufacturing feasibility through standardized shroud components.
Data Source
Figure 1
AI summary
The present invention relates to a blade cascade for a turbomachine, in particular a gas turbine, having a number of first blade arrangements (120), each having at least one first blade (100) and one first shroud (10) having a first extension (T1) in the circumferential and/or axial direction, and each having a number of second blade arrangements (220), each having at least one second blade (200) and one second shroud (20) having a second extension (T2) in the same direction which is larger than the first extension, at least one of the first blades being designed to be stiffer torsionally than at least one of the second blades.