Centrifugal Compressor Cover Attachment Using Flexible Diaphragm
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Solution Overview
Problem
The existing methods for attaching a turbomachine centrifugal compressor cover fail to maintain a constant and minimal clearance between the cover and the impeller across various flight phases due to temperature and pressure gradients, as well as centrifugal forces, leading to inefficiencies and potential contact issues.
Innovation Solution
A centrifugal compressor cover with a fastener configuration featuring a double elbow joint and an axisymmetric diaphragm, where the diaphragm is fixed to the turbine casing with a frustoconical arm and a radial crown, allowing for adjustable clearance and flexibility to maintain a constant distance from the impeller fins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the cover is rigidly fixed to the casing, then the structural stability is improved, but the clearance between the cover and impeller varies significantly during operation
Solution Approach 1:
The attachment system transitions from a rigid fixed connection to a dynamic flexible connection that allows the cover to move radially and axially. The diaphragm and elbow joint create a compliant mechanism that adapts the cover position to impeller deformation, maintaining consistent clearance while the overall structure remains stable.
Solution Approach 2:
The attachment system changes its physical parameters (flexibility, radial displacement capability, axial movement) to adapt to operating conditions. The diaphragm's flexibility and the elbow joint's angular adjustment allow the cover to follow impeller movement, transforming the rigid parameter relationship into a variable one that maintains optimal clearance.
2Productivity
If the cover clearance is minimized at maximum power, then the efficiency at PMD is improved, but the clearance becomes too small at intermediate and transient regimes
Solution Approach 1:
The flexible attachment system dynamically adjusts the cover position based on impeller deformation at different operating regimes. At maximum power, the cover follows the impeller's radial expansion and fin inclination, maintaining minimal clearance. At intermediate and transient regimes, the system allows sufficient clearance to prevent contact while preserving efficiency.
Solution Approach 2:
The attachment system's physical state changes with operating conditions, allowing radial displacement and angular adjustment of the elbow joint. This enables the clearance to be optimized for each regime: minimal at maximum power for efficiency, and adequate at other regimes to prevent contact, rather than being fixed at a compromise value.
3Device complexity
If a rigid attachment is used, then the manufacturing complexity is reduced, but the ability to accommodate impeller movement is lost
Solution Approach 1:
The diaphragm serves as a flexible element that replaces complex rigid mechanisms. This thin-walled flexible structure accommodates radial and axial movements of the cover while maintaining structural integrity, providing adaptability with relatively simple construction compared to articulated rigid mechanisms.
Solution Approach 2:
The attachment system incorporates dynamic elements (flexible diaphragm, articulated elbow joint) that enable the cover to move and adapt to impeller deformation. This dynamic capability is achieved through a relatively simple mechanism combining flexibility and a single angular joint, avoiding the need for complex multi-degree-of-freedom mechanisms.
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
This configuration significantly reduces clearance variations, achieving a 54% reduction in play at intermediate speeds and ensuring optimal engine performance by allowing the cover to follow the impeller's movement and deformation, thereby maintaining a minimal and consistent clearance.
Implementation Method 1
The impeller cover clips are configured as flexible diaphragms to accommodate cover positioning during centrifugal compressor operation
Implementation Method 2
the temperature and pressure of the airflow in a centrifugal compressor impeller increases substantially 30-40% from the leading edge to the trailing edge of the impeller. The effect of this differential is to tilt the radial portions of the fins close to the trailing edge upstream
Implementation Method 3
These centrifugal forces also induce radial expansion, in particular for the axial portion of the cover, on the side of its leading edge
Data Source
Figure 1~2
Figure 3~4
AI summary
The aim of the present invention is to enable the cover of a centrifugal compressor to be moved such that the clearance between the cover and the blades of the compressor impeller remains substantially constant and as low as possible. To achieve said aim, the invention provides an attachment arrangement at the middle of the cover having an elastically deformable portion. A cover has a concave shell (50) having an inner surface (51) spaced apart from the compressor (12) provided with an impeller (22) having blades (20) by an attachment (8). The attachment (8) has one connection end (83) at the middle of the shell (50), and another end (82) attached to a casing (6) of the turbine engine (1). The attachment (8) comprises an axisymmetric diaphragm (80) having a generally frusto-conical configuration having an arm profile (8b) coupled to the end for attachment (82) to the casing (6) by a double-elbow joint (8c, 8d, 8e) having right and obtuse angles when in the rest position. The distance between the inner surface (51) of the shell (50) and the upper edges (21) of the blades (20) can be held constant during operation with minimum clearance adjustment.