Bladed Rotor Under-Platform Dampers for Flutter Stabilization
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Solution Overview
Problem
Turbine blades in turbomachines are prone to flutter due to negative aerodynamic damping, which can lead to excessive vibration and failure from high cycle fatigue, and existing alternate frequency mistuning methods are not fully effective in stabilizing these vibrations.
Innovation Solution
A bladed rotor system with under-platform dampers featuring alternate sets of solid and hollow dampers, or hybrid dampers with varying material distributions, positioned in a periodic pattern to provide frequency mistuning and stabilize flutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If identical blades are assembled into the rotor disc, then manufacturing simplicity is maintained, but blade flutter occurs due to negative aerodynamic damping
Solution Approach 1:
The patent applies local quality by introducing alternate frequency mistuning only to specific blades in the rotor disc, rather than modifying all blades uniformly. Selected blades have adjusted mass or geometry parameters to create frequency alternation, while other blades remain identical to the original design, thus maintaining manufacturing simplicity for the majority of components while providing localized flutter stabilization.
Solution Approach 2:
The patent implements parameter changes by modifying the mass or geometric parameters of selected blades to alter their natural frequencies. This creates an alternate frequency distribution across the blade row, transforming the uniform frequency characteristic of identical blades into a mistuned pattern that stabilizes aerodynamic damping and prevents flutter.
2Reliability
If alternate frequency mistuning is implemented by modifying blade mass and geometry, then flutter stability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the blade population into distinct groups: mistuned blades with modified parameters and untuned identical blades. This segmentation allows the complex mistuning to be applied only where necessary for flutter control, while the majority of blades can be manufactured using standard processes, thereby reducing overall manufacturing complexity compared to modifying all blades.
Solution Approach 2:
The patent implements universality by designing the mistuned blades to maintain compatibility with the standard blade mounting and aerodynamic interface. The modified blades serve multiple functions: they provide the necessary frequency mistuning for flutter stabilization while still functioning as standard aerodynamic airfoils and maintaining structural compatibility with the rotor disc assembly.
3Reliability
If mistuned blades are designed with predetermined frequency alternation, then aerodynamic damping is stabilized, but design complexity increases
Solution Approach 1:
The patent applies periodic action by arranging the mistuned and untuned blades in an alternating periodic pattern around the rotor disc. This periodic distribution of frequency variations creates a systematic mistuning pattern that effectively stabilizes aerodynamic damping across the blade row, transforming the complex interaction of random variations into a controlled periodic structure that is easier to analyze and design.
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 solution effectively stabilizes blade vibrations by introducing alternate frequency mistuning, ensuring positive aerodynamic damping and improved flutter resistance, allowing for the design of blades with predetermined frequency alternation without compromising aerodynamic efficiency.
Implementation Method 1
An important source of damping in the modes is from aerodynamic forces acting on the blades when the blades vibrate. Under certain conditions, the aerodynamic damping in some of the modes may become negative, which may cause the blades to flutter.
Implementation Method 2
Alternate frequency mistuning can cause system modes to be distorted, so that the resulting new, mistuned system modes are stable, i.e., they all have positive aerodynamic damping.
Data Source
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AI summary
A bladed rotor system (10) for a turbomachine includes a circumferential row of blades (14) mounted on a rotor disc (12), and includes a plurality of under-platform dampers (30). Each damper (30) is located between adjacent blade platforms (24). The plurality of dampers (30) includes a first set (H) of dampers (30) and a second set (L) of dampers (30). The dampers (30) of the first set (H) are distinguished from the dampers (30) of the second set (L) by a cross- sectional material distribution in the damper (30) that is unique to the respective set (H, L). Dampers (30) of the first set (H) and the second set (L) are positioned alternately in a periodic fashion in a circumferential direction, to provide a frequency mistuning to stabilize flutter of the blades (14).