Stator Vane Boss Cross-Section for Casting
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Solution Overview
Problem
The existing methods for producing stator vane arrangements in turbomachines face challenges in controlling the position of ceramic cores during the investment casting process, leading to reduced thickness of walls around passages and the formation of dimples due to uneven cooling, which requires additional machining to achieve the correct shape.
Innovation Solution
The stator vane arrangement features bosses with a first portion having a smaller cross-sectional area and a second portion with a larger cross-sectional area, positioned between the first portion and the radially inner annular structure, along with support structures to maintain alignment and minimize machining stresses, using a wax pattern and ceramic cores to ensure precise positioning during casting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bosses are provided on the radially inner surface of the radially inner annular wall to supply lubricant and air, then the bearing housing can be supported and lubricated, but the wall thickness around the passages is reduced and dimples form due to uneven cooling during solidification
Solution Approach 1:
The boss is designed with varying cross-sectional areas along its length, creating different local thicknesses. The first portion has a smaller cross-sectional area while the second portion has a larger cross-sectional area, allowing different regions of the boss to serve different functions - the thinner first portion allows better cooling and lubricant flow, while the thicker second portion maintains structural integrity and prevents dimple formation
2Weight of moving object
If the radially inner annular structure is made thinner to reduce weight, then the overall weight of the stator vane arrangement is reduced, but the structural strength and ability to support bearing housing is compromised
Solution Approach 1:
The boss structure is made asymmetric with varying cross-sectional areas rather than being uniform throughout. The first portion has a smaller cross-sectional area optimized for weight reduction and flow, while the second portion has a larger cross-sectional area optimized for strength and support, creating an asymmetric geometry that optimizes both weight and strength requirements
3Manufacturing precision
If additional machining is performed to correct dimples on the radially outer surface, then the correct shape is achieved, but the production time and cost increase
Solution Approach 1:
The boss geometry is pre-designed with varying cross-sectional areas during the casting process itself, rather than attempting to correct defects afterward. The first portion with smaller cross-sectional area is deliberately created to allow faster cooling in that region, preventing dimple formation in the first place. This preliminary design approach eliminates the need for subsequent corrective machining operations
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 solution reduces the weight of the stator vane arrangement by optimizing the thickness of the radially inner annular structure, allows for adjustable dimensions, and minimizes machining stresses, resulting in a more efficient and cost-effective production process with improved flow areas for lubricant and air passage.
Implementation Method 1
During the solidification of the molten metal during the casting process the molten metal in the thinner regions cools quicker than the molten metal in the thicker regions
Data Source
AI summary
A stator vane arrangement for a turbomachine comprises a radially inner annular structure, a radially outer annular structure and a plurality of circumferentially spaced vanes extending radially between the inner annular structure and the outer annular structure. At least one of the vanes has a passage extending from the inner annular structure to the outer annular structure. The inner annular structure has at least one radially inwardly extending boss and each boss has a passage extending there-through. The passage in each boss is aligned with a corresponding passage in a vane. Each boss comprises a first portion having a first cross-sectional area and a second portion having a second cross-sectional area which is greater than the first cross-sectional area. The first portion of each boss is positioned between and interconnecting the second portion of the boss and the inner annular structure.