Asymmetrical Casing Structuring for Compressor Blade Flutter Stability
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Solution Overview
Problem
Fluid-flow machines, such as compressors in jet engines, experience structural vibration excitations due to fluid-mechanic forces, leading to reduced flutter stability and efficiency, with slender blades being particularly prone to non-synchronous vibrations and flutter, which limits their working range and increases weight and costs.
Innovation Solution
A circumferentially asymmetrical structuring of the annular space surface in the circumferential casing of fluid-flow machines, which improves the flutter stability of rotor blades by reducing gap swirl losses and allowing for a broader working range, reduced weight, and lower costs through optimized design and potential reduction in the number of rotor blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the annular space surface is designed smooth, then manufacturing is easier, but flutter stability of rotor blades deteriorates
Solution Approach 1:
The patent applies asymmetry by designing the annular space surface with a circumferentially asymmetrical structuring instead of a smooth or symmetric surface. This asymmetrical structuring disrupts the formation of stationary gap swirls that cause synchronous and non-synchronous blade vibrations, thereby improving flutter stability while maintaining manufacturing feasibility through defined groove patterns.
Solution Approach 2:
The patent applies local quality by implementing structuring only in specific regions of the annular space surface, particularly in the blade tip area where gap swirls form. The structuring consists of grooves with specific geometries (depth, width, spacing) localized to where they are most effective at reducing vibrations, rather than applying uniform treatment across the entire surface.
2Power
If the number of rotor blades is increased, then power density increases, but weight and costs increase
Solution Approach 1:
The patent applies parameter changes by modifying the geometric parameters of the annular space surface structuring (groove depth, width, spacing, and asymmetry characteristics) to optimize the interaction between the casing and rotor blade tip flows. These parameter changes improve flutter stability and allow for optimized rotor blade designs that can achieve required power density with reduced blade counts.
3Productivity
If the working range is expanded, then efficiency increases, but flutter stability requirements become more stringent
Solution Approach 1:
The patent applies preliminary action by implementing the asymmetrical structuring of the annular space surface before the rotor blades operate in the expanded working range. This pre-configured surface structure proactively prevents the formation of harmful gap swirls and vibrations across the entire expanded operating envelope, ensuring flutter stability is maintained throughout the extended working range rather than requiring corrective measures during operation.
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 circumferentially asymmetrical design enhances flutter stability, expands the working range of compressors, increases efficiency, and reduces weight and costs by minimizing vibration excitations and gap swirl losses, thereby improving the operational performance of fluid-flow machines.
Implementation Method 1
The smooth annular space surface leads to the formation of a stationary gap swirl at the blade tip, which promotes buildup of a blockage in the blade passage
Implementation Method 2
The circumferential casing has on the inside a structuring formed by grooves running in the circumferential direction. This is intended to influence the boundary layer in the blade tip area.
Data Source
AI summary
A fluid-flow machine includes at least one rotor having a rotary element with a plurality of rotor blades arranged on the rotary element, and a circumferential casing having a central axis and surrounding the rotor. The circumferential casing or a part connected thereto has an annular space surface on the inside, which delimits a flow duct of the fluid-flow machine radially outwards. The annular space surface has a structuring at least in one area adjoining a rotor on the circumferential side. At least one structuring of the annular space surface has, relative to the central axis of the circumferential casing, a circumferentially asymmetrical design.