Axial-Flow Rotor Blade Stacking Line Design
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Solution Overview
Problem
Conventional rotor blades in axial-flow fluid machines experience increased secondary flow loss near the hub portion due to the inclination of the stacking line, which affects the reduction of bending stress.
Innovation Solution
The rotor blade features a stacking line that remains parallel to the radial direction up to 20% of the blade height from the hub portion and then gradually curves towards the suction-side surface in the circumferential direction, avoiding the secondary flow region near the hub-side end wall, thereby reducing bending stress and secondary flow loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the stacking line is inclined towards the suction-side surface to reduce bending stress, then bending stress is reduced, but secondary flow loss increases
Solution Approach 1:
The blade span is divided into two distinct regions: a hub-side region (0-20% span) where the stacking line is parallel to the radial direction to minimize secondary flow loss, and a tip-side region (20-100% span) where the stacking line curves toward the suction side to reduce bending stress. This segmentation allows each region to be optimized independently for its dominant concern.
Solution Approach 2:
Different portions of the blade span are assigned different stacking line characteristics tailored to local requirements: the hub portion uses a radial parallel stacking line to preserve secondary flow characteristics, while the outer portion uses a curved stacking line to reduce bending stress. This local differentiation resolves the contradiction by applying the appropriate stacking line style to each local region.
2Loss of energy
If the stacking line remains parallel to the radial direction near the hub, then secondary flow loss is reduced, but bending stress reduction is compromised
Solution Approach 1:
The blade is segmented into hub-side and tip-side regions with different stacking line characteristics. The hub-side region (0-20% span) maintains radial parallel stacking to minimize secondary flow loss, while the tip-side region (20-100% span) curves toward the suction side to reduce bending stress, achieving both objectives in their respective zones.
Solution Approach 2:
Instead of applying the curved stacking line throughout the entire blade span, the invention applies it only partially in the outer 80% of the span, leaving the inner 20% with radial parallel stacking. This partial application of the curvature resolves the contradiction by limiting the curvature effect to regions where it provides benefit without causing harmful secondary flows.
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 effectively reduces bending stress and secondary flow loss, maintaining the stress reduction benefits while minimizing the impact on secondary flows near the hub-side end wall.
Implementation Method 1
The slopes of the portions are of opposite signs. The arrangement provides a compressive component of bending stress on the trailing and leading edges due to centrifugal forces when in use.
Implementation Method 2
since the pressure (static pressure) of combustion gas flowing through the mainstream flow path is relatively high on the pressure-side surface PS of the blade portion AF and is relatively low on the suction-side surface SS, a gas force caused by the pressure difference between both the aforementioned surfaces acts on the blade portion AF.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
Provided is a rotor blade of an axial-flow fluid machine capable of maintaining an effect of reducing a bending stress acting on a blade portion and reducing a secondary flow loss in the vicinity of a hub-side end wall. A rotor blade (RBX) includes a blade portion (AFX) that extends in a spanwise direction from a hub portion to a tip portion and has a pressure-side surface (PSX) and a suction-side surface (SSX), a blade portion is formed by profiles (PX) with airfoil shapes stacked in the spanwise direction, and a stacking line (SLX) connecting gravity centers (GX) of the profiles at each spanwise position is a straight line parallel to a radial direction at a part from the hub portion to an outer end of a secondary flow region in a vicinity of the hub portion, and is a curved line, along which a distance measured from the straight line parallel to the radial direction toward a side of the suction-side surface gradually increases toward the tip portion, at a part from the outer end of the secondary flow region to the tip portion.