Turbomachine Blade Platforms With Oblong Friction Damping Openings
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Solution Overview
Problem
Existing bladed turbomachine assemblies, particularly those with composite material blades, face issues with vibration damping that lead to mechanical stress and separation of circumferentially adjacent platforms due to varying contact forces during operation, which are exacerbated by the low stress tolerance of composite materials and thermal expansion differences.
Innovation Solution
A bladed assembly design featuring platforms with oblong openings and friction members that allow circumferential displacement, engaging with clearance, to generate friction and limit relative motion, thereby dissipating vibration energy and reducing stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex interlock profiles with non-axial portions are used to dampen vibrations through friction, then vibration damping is improved, but blade stress increases and composite material blades become intolerant due to pretorsion
Solution Approach 1:
The friction mechanism is segmented from the blade platform structure. Instead of using complex interlock profiles on the platform itself, a separate friction member is introduced that can move independently within an oblong opening, providing vibration damping without imposing pretorsion stresses on the blade
Solution Approach 2:
A dedicated friction member acts as an intermediary element between the blade platform and the vibration source. This friction member engages with the oblong opening to provide frictional damping while being decoupled from the blade structure, thus protecting composite material blades from excessive stress
2Reliability
If platforms are configured with complex interlock profiles to generate contact force for vibration damping, then vibration damping is improved, but gas flow is disturbed due to damping pieces extending into the flow path
Solution Approach 1:
The friction mechanism is extracted from the gas flow path. The oblong opening is configured so that the friction member moves entirely within the opening, which is positioned such that the friction member never protrudes into the gas flow, thereby eliminating flow disturbance while maintaining vibration damping
Solution Approach 2:
The friction member is constrained to move within the plane of the platform by the oblong opening geometry, rather than extending axially into the gas flow path. This dimensional constraint keeps the damping mechanism out of the flow path while maintaining its vibration damping function
3Object-generated harmful factors
If cavities with closed cross-section are used to house damping elements, then gas flow is not interfered with, but platform weight increases due to large material volume required
Solution Approach 1:
The damping function is segmented from the platform structure itself. Instead of creating large cavities within the platform, a separate friction member is used that engages with a simple oblong opening, significantly reducing the material volume required while maintaining the vibration damping function
Solution Approach 2:
The oblong opening is positioned at the circumferential end of the platform where it is needed for the friction mechanism, rather than creating large cavities throughout the platform structure. This localized approach minimizes material removal and maintains platform strength while enabling the damping function
4Productivity
If CMC blades are used to reduce weight, then productivity and efficiency are improved, but vibration damping becomes more difficult due to low stress tolerance and poor tolerance of pretorsion
Solution Approach 1:
The vibration damping function is segmented from the CMC blade structure itself. A separate friction member is introduced that interacts with the blade through a simple oblong opening, providing damping without requiring complex interlock profiles that would induce pretorsion stresses in the sensitive CMC material
Solution Approach 2:
The friction member serves as an intermediary that provides vibration damping protection to CMC blades. It absorbs the vibrational energy through friction while engaging with the blade through a simple geometric interface (oblong opening) that does not concentrate stress or induce pretorsion in the composite material
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 dampens vibrations and reduces mechanical stress on blades by allowing frictional energy dissipation without interfering with the gas flow or increasing platform weight, suitable for composite material blades.
Implementation Method 1
the friction member being engaged through the opening formed in the platform of a circumferentially adjacent blade with a clearance allowing at least one displacement of the friction member in the circumferential direction within the opening
Implementation Method 2
bearing under the other platform under the effect of the centrifugal force in operation and thus exerting friction forces
Data Source
Figure 1~5
Figure 2~3A
Figure 3B~4
AI summary
A bladed assembly (40) for a turbomachine comprises a plurality of blades (42) distributed around an axis (28) and each comprising a vane (44) and a platform (46) formed at a free end of the blade (42). The platform (46) of each blade comprises a friction member (70) and an opening (72) that is oblong in a circumferential direction (C) with respect to the axis (28). The friction member (70) is engaged through the opening (72) formed in the platform (46) of a circumferentially adjacent blade (42) within the bladed assembly (40) with a clearance allowing the friction member (70) to move at least in the circumferential direction (C) within the opening (72). Mutual separation of the platforms (46) in the circumferential direction in operation due to vibrations of the blades causes the friction member 70 to rub against an edge of the opening 72 and thereby dissipate energy.