Axial Turbine Stator Vane Stress Reduction via Hub Shift
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Solution Overview
Problem
The stator vane segment of an axial turbine experiences stress on the suction surface near the hub portion due to thermal expansion, leading to deformation and reduced aerodynamic performance, which cannot be effectively mitigated by increasing the airfoil portion thickness without increasing weight.
Innovation Solution
The stator vane segment features a stacking line that shifts from the pressure surface to the suction surface in the circumferential direction near the hub portion, reducing stress on the suction surface without increasing weight, achieved by forming airfoil profiles with a straight trailing edge that transitions smoothly into a circumferential shift, specifically up to 50% Pitch at the hub portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the airfoil portion thickness is increased to reduce stress on the suction surface, then the stress resistance is improved, but the weight of the stator vane segment increases
Solution Approach 1:
The patent applies different thickness distributions to different regions of the airfoil portion. The thickness is increased specifically in the hub portion region where stress concentration occurs due to thermal expansion, while maintaining optimal thickness in other regions. This localized thickness adjustment reduces stress without proportionally increasing the overall weight of the stator vane segment.
Solution Approach 2:
The patent modifies the thickness parameter of the airfoil portion as a function of position, specifically increasing thickness near the hub portion where thermal expansion stresses are most severe. This parameter change allows the structure to better resist thermal stresses while minimizing unnecessary material addition and weight increase.
2Productivity
If the stator vane segment is formed as a coupled vane with multiple airfoil portions, then the aerodynamic performance is improved, but the stress concentration on the suction surface near the hub portion increases due to thermal expansion
Solution Approach 1:
The patent addresses stress concentration at specific locations (suction surface near hub portion) while maintaining the coupled vane configuration for aerodynamic performance. By locally adjusting thickness in the hub region, the patent reduces stress concentration without altering the overall multi-airfoil coupled vane structure that provides aerodynamic efficiency.
Solution Approach 2:
The patent divides the stator vane segment into multiple airfoil portions (first, second, and third airfoil portions) with different thickness characteristics. The third airfoil portion, located at the circumferential end, has increased thickness to handle thermal expansion stresses, while other portions maintain optimized thickness for aerodynamic performance.
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 reduces stress on the suction surface near the hub portion and minimizes total pressure loss due to secondary flow, maintaining aerodynamic performance without weight increase, as demonstrated by computational fluid dynamics analysis.
Implementation Method 1
the radially outer side of the inner band is largely thermally expanded in the circumferential direction as compared with the radially inner side
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
In a stator vane segment of an axial turbine formed in a coupled vane, stress generated on a suction surface near a hub portion of an airfoil portions having a suction surface located on a circumferential end side of an inner band is reduced without causing increase in weight. The stator vane segment includes: a plurality of airfoil portions; and one outer band and one inner band joined to a tip portion and a hub portion of each of the airfoil portions, wherein each of the airfoil portions is formed by stacking airfoil profiles in a spanwise direction from the hub portion to the tip portion, and each of the profiles includes a leading edge and a trailing edge, and a pressure surface and a suction surface, in a stacking line obtained by connecting the respective trailing edges of the profiles at spanwise positions, a portion from the tip portion to a predetermined position is a straight line parallel to a radial direction of the axial turbine, a portion from the predetermined position to the hub portion is shifted from the pressure surface toward the suction surface in a circumferential direction from the straight line parallel to the radial direction, and an amount of the shift monotonically increases from the predetermined position to the hub portion.