Turbomachine Exhaust Casing Hub Cavity Sealing
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Solution Overview
Problem
The exhaust casing of turbomachines experiences air infiltration into the hub cavity, leading to thermal gradients that reduce the lifespan of radial arms and causes vibrations due to resonance with rotor frequencies, negatively impacting fuel consumption and mechanical integrity.
Innovation Solution
A turbomachine exhaust casing design featuring a cylindrical jacket with a radially sliding annular rim that seals the hub cavity, minimizing air infiltration and preventing resonance by axially securing the jacket, which includes annular flanges and elastic prestressing to manage thermal expansion and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the radial annular portion of the cylindrical jacket is left free, then the结构简单性 (structural simplicity) is maintained, but air infiltration into the hub cavity occurs causing thermal gradients and resonance vibrations
Solution Approach 1:
The annular rim is designed to slide radially within the annular groove, transforming the static sealing problem into a dynamic solution. This allows the sealing interface to adapt to thermal expansion while maintaining密封 effectiveness, resolving the contradiction between simple structure and reliable sealing.
Solution Approach 2:
The radial sliding connection explicitly accommodates thermal expansion of the cylindrical jacket. The annular rim can move radially within the groove to compensate for dimension changes due to temperature variations, preventing stress concentration while maintaining sealing.
2Duration of action of stationary object
If the radial annular portion is free, then manufacturing is simpler, but thermal gradients in radial arms increase reducing their lifetime
Solution Approach 1:
The sealing structure is segmented into distinct components: the annular rim, the annular groove, and the two annular flanges. This segmentation allows each component to be manufactured and assembled independently, simplifying the overall manufacturing process while achieving the sealing function.
3Reliability
If the radial annular portion is free, then the structure is simpler, but vibration frequencies match rotor frequencies causing resonance
Solution Approach 1:
The upstream annular flange preliminarily positions and secures the cylindrical jacket axially before operation begins. This preliminary action raises the vibration frequencies of the jacket above rotor frequencies, preventing resonance while maintaining structural simplicity.
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 design minimizes thermal gradients, reduces air intake from compressors, and raises vibration frequencies to prevent resonance, thereby extending the lifespan of radial arms and the cylindrical jacket while maintaining efficient operation.
Implementation Method 1
sliding radially in substantially sealed manner
Implementation Method 2
thermal expansion that takes place at the operating temperatures of the turbomachine
Implementation Method 3
radially sliding connection serves to provide good sealing for the hub cavity, while avoiding mechanical stresses appearing in the cylindrical jacket
Implementation Method 4
holding the upstream end of the cylindrical jacket axially serves to raise the frequencies of the vibration modes of the jacket, thereby avoiding resonance phenomena
Data Source
AI summary
The exhaust casing of a turbomachine includes a cylindrical jacket for guiding a flow of exhaust gas and for defining a hub cavity inside the casing, the jacket including at its ends an annular flange and a radial annular portion extending inwards and formed with an annular rim that is designed to be received in an annular groove of the inner wall of the exhaust casing to close the hub cavity in substantially sealed manner.