Gas Turbine Aerofoil Array with Detuned Eigenfrequencies
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Solution Overview
Problem
Gas turbine aerofoil arrays face instability due to low rigidity and sensitivity to aeroelastic vibrations, leading to structural stress and noise, with existing solutions either compromising aerodynamic efficiency or being costly and complex to produce.
Innovation Solution
An aerofoil array design with monolithic, identically shaped central portions and geometrically distinct outer ends, forming an inner and outer annular platform, which detunes eigenfrequencies without altering the central cross-sections, maintaining aerodynamic efficiency and stability while allowing for an interconnected rotor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If aerofoils are made with smaller thicknesses to reduce weight, then weight is reduced, but rigidity decreases leading to aeroelastic instability
Solution Approach 1:
The aerofoils are designed with non-uniform thickness distribution, having smaller thicknesses at the roots for weight reduction and larger thicknesses at the tips for rigidity enhancement. This local variation in geometric properties allows simultaneous optimization of both weight and structural strength without compromising aeroelastic stability
Solution Approach 2:
The invention employs aerofoils with asymmetric cross-sectional geometry where the thickness distribution is intentionally made non-symmetric along the span. This asymmetric design creates differential rigidity characteristics that suppress aeroelastic flutter while maintaining reduced overall weight compared to uniform thick designs
2Stability of the object's composition
If aerofoil geometry is varied to detune eigenfrequencies and reduce flutter, then vibration stability improves, but aerodynamic efficiency decreases
Solution Approach 1:
Geometric variations are applied locally at specific regions of the aerofoils rather than uniformly across all aerofoils. This localized detuning approach modifies eigenfrequencies to suppress flutter while preserving the overall aerodynamic efficiency of the majority of the aerofoil surface area
Solution Approach 2:
Instead of varying the geometry of all aerofoils completely, the invention applies geometric variations to only a subset or partial portion of the aerofoils. This partial action is sufficient to achieve the required detuning effect for flutter suppression while minimizing the impact on aerodynamic performance
3Stability of the object's composition
If recesses are made in radial ends of aerofoils to detune frequencies, then flutter is reduced, but production time and costs increase
Solution Approach 1:
The desired geometric variations are incorporated into the aerofoil design from the initial manufacturing stage rather than requiring subsequent machining operations. This preliminary action allows the detuned geometry to be achieved directly through casting or forming processes, eliminating the need for additional recess machining operations
Solution Approach 2:
The invention extracts the essential function of frequency detuning from the complex machining operation of creating recesses and replaces it with a simpler geometric modification that can be achieved through standard manufacturing processes, thereby removing the production complexity while retaining the flutter suppression benefit
4Stability of the object's composition
If different geometrical characteristics are assigned to aerofoils of first and second sets, then detuning is achieved, but storage and handling systems become more complex
Solution Approach 1:
The invention maintains a high degree of homogeneity among all aerofoils by using identical or substantially similar geometric characteristics for the majority of the structure. This homogeneity allows all aerofoils to be stored, handled, and installed using the same systems and procedures, while minor geometric variations are introduced only where needed for detuning purposes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design enhances aeroelastic stability and maintains high aerodynamic efficiency without increasing weight, allowing for an interconnected rotor and simplified production, addressing the limitations of previous solutions.
Implementation Method 1
this instability is due to marked sensitivity to aeroelastic phenomena deriving from aerodynamic interactions between the aerofoils of a same turbine stage, with the consequent triggering of vibrations that stress the arrays
Implementation Method 2
This phenomenon of self-induced aeroelastic vibrations, known as flutter, thus defines a constraint in the design of arrays
Data Source
Figure 1
Figure 2~3
Figure 3A~3B
AI summary
An aerofoil array for a gas turbine system has an inner annular platform (3a) and an outer annular platform (4a), which extend about a longitudinal axis (la) and radially delimit an annular channel (5) for a gas flow; the annular channel houses a plurality of aerofoils, arranged at a substantially constant angular pitch and comprising respective central portions (7a, 7b) and respective ends (8a, 8b) connected to the platforms (3a, 4a); the aerofoils are formed by two series of aerofoils (5a, 5b) having a different geometrical feature in order to intentionally vary the eigenfreguencies and arranged about the longitudinal axis (la) with a sequence that is regularly repeated all along the annular channel (5); even though the external geometry of the aerofoils (5a, 5b) is varied, the cross-sections (9a, 9b) remain unchanged in the central portions (7a, 7b), at any given radius with respect to the longitudinal axis (la).