Francis Runner Blade Drainage for Axial Thrust Reduction
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Solution Overview
Problem
Hydraulic machines with radial flow Francis-type runners face significant axial thrust due to imperfect sealing, making existing balancing solutions like pipes and holes either expensive or ineffective, especially in modernization projects where new blade geometries and space constraints are involved.
Innovation Solution
Incorporating passages within the runner blades that lead from the crown to the trailing edge, allowing high-pressure leakage water to drain to the low-pressure side, reducing drag and axial thrust through a designed inlet aperture and continuous opening that minimizes backpressure and radial pumping effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If balancing pipes are used to drain leakage water, then axial thrust is reduced, but device complexity and cost increase
Solution Approach 1:
The patent merges the thrust balancing function with the runner blade structure itself by integrating passages directly into the blade. This eliminates the need for separate balancing pipes and external drainage systems, thereby reducing device complexity while maintaining the ability to drain leakage water and reduce axial thrust.
Solution Approach 2:
The patent extracts the drainage function from separate balancing pipes and integrates it directly into the runner blade structure. By taking out the drainage function and embedding it within the blade passages, the system achieves thrust reduction without requiring additional external components.
2Force
If balancing holes are used in the runner crown, then axial thrust is reduced, but manufacturing precision and effectiveness vary with revolution speed and blade geometry
Solution Approach 1:
The patent applies local quality by positioning passages specifically within the runner blade structure where they can directly intercept and drain leakage water. The passages are strategically located to optimize drainage efficiency at different revolution speeds and blade geometries, ensuring consistent thrust reduction performance across varying operating conditions.
3Productivity
If new blade geometries with trailing edges closer to the axis are used, then hydraulic efficiency is improved, but space for traditional balancing holes is reduced
Solution Approach 1:
The patent merges the thrust balancing function with the runner blade structure itself by integrating passages directly into the blade. This eliminates the need for separate balancing pipes and external drainage systems, thereby reducing device complexity while maintaining the ability to drain leakage water and reduce axial thrust.
Solution Approach 2:
The patent transitions from the traditional approach of placing balancing holes in the runner crown (horizontal dimension) to integrating passages within the runner blade structure (vertical/three-dimensional integration). This dimensional change allows efficient drainage without requiring additional space in the runner crown, enabling the use of modern blade geometries with improved hydraulic efficiency.
4Force
If passages lead to the runner hub, then axial thrust is reduced, but radial pumping effects increase backpressure
Solution Approach 1:
The patent inverts the traditional drainage approach by having passages lead from the runner crown through the blade to the trailing edge, rather than leading to the runner hub. This reversal of the drainage path eliminates the radial pumping effects that cause backpressure, allowing leakage water to drain efficiently without creating additional pressure resistance.
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 effectively reduces axial thrust by efficiently draining leakage water, improving hydraulic efficiency and being more cost-effective and adaptable than traditional balancing methods, particularly in modernization projects with constrained spaces.
Implementation Method 1
water can get in the space between the head cover of the hydraulic machine and the runner crown resulting in a high axial thrust
Implementation Method 2
the passage comprises an inlet aperture located in a portion of the crown which during operation is exposed to high pressure leakage water
Implementation Method 3
having leakage water exiting the trailing edge may reduce drag forces as the runner rotates and result in an improvement in hydraulic efficiency
Data Source
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AI summary
A runner of Francis type, comprising a crown, a plurality of blades, each blade being defined by a pressure surface, an suction surface, an edge adjoining the high pressure side and a spaced apart edge adjoining the low pressure side, whereas the crown comprises sealing means to seal the space above the crown against water from the high pressure side, whereas the runner comprises at least one passage being capable to drain high pressure leakage water to the low pressure side, and the passage comprises an inlet aperture located in a portion of the crown which is exposed to high pressure leakage water, whereas the passage is located within a blade and leads from the inlet aperture to the edge of the same blade adjoining to the low pressure side, whereas the passage is shaped to form a continuous opening in the same edge adjoining to the low pressure side.