Francis Turbine Guide Vane Negative Curvature Flow Separation
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Solution Overview
Problem
In Francis turbines, the existing guide vane designs often lead to flow separation and increased friction loss due to complex flow channel configurations and local increases in flow velocity, which affect the efficiency of energy conversion and power generation.
Innovation Solution
The guide vane design incorporates a negative curvature portion on the runner side vane surface, extending from the upper to the lower end, to mitigate local flow velocity increases and prevent flow separation, thereby reducing friction loss and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the vane surface is formed to be convex (or straight) to prevent flow separation, then flow separation is prevented, but the flow channel configuration becomes complex causing local flow velocity increases and friction loss
Solution Approach 1:
The patent applies local quality by creating a concave portion at a specific location (the outlet end) of the runner side vane surface, while maintaining convexity in other regions. This localized modification allows the flow to smoothly exit the vane without creating complex flow patterns throughout the entire surface, thereby reducing friction loss while preventing flow separation at the critical outlet region.
Solution Approach 2:
The patent utilizes curvature by introducing a concave portion with specific curvature characteristics at the outlet end of the runner side vane surface. This curved design allows the flow to follow the contour of the vane surface more smoothly, reducing abrupt changes in flow direction and velocity, thereby minimizing friction loss while maintaining flow separation prevention.
2Ease of operation
If the guide vane opening is reduced to control water flow, then power generation control is improved, but flow separation occurs on the inner circumferential side causing flow channel narrowing
Solution Approach 1:
The concave portion at the outlet end of the runner side vane surface creates a localized flow acceleration zone that helps maintain smooth flow even when the overall guide vane opening is reduced. This local modification prevents flow separation at the critical outlet region, allowing the flow channel to remain stable and open even at lower operating conditions.
3Productivity
If the guide vane opening is increased to maximize water flow, then power generation capacity is improved, but flow separation occurs on the outer circumferential side causing flow channel narrowing
Solution Approach 1:
The concave portion at the outlet end provides a localized flow management mechanism that prevents flow separation on the outer circumferential side even when the guide vane opening is maximized. This local design feature ensures that the flow channel remains stable and functional across the entire range of operating conditions, from partial to full opening.
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
The negative curvature portion effectively suppresses friction loss and improves the overall efficiency of the Francis turbine by maintaining smooth water flow and preventing flow separation, leading to increased power generation capabilities.
Implementation Method 1
the angle at which water flows into the flow channels defined between the guide vanes 51 and the inlet angle of the guide vanes 51 are caused to deviate, resulting in fears that a flow separation occurs depending on situations
Implementation Method 2
An increase in flow velocity like this causes a problem in which the friction loss is increased
Data Source
AI summary
In a guide vane according to an embodiment of the invention, where in a section perpendicular to a guide vane rotation axis, a curvature of a contour line forming a runner side vane surface of the guide vane is referred to as a positive curvature when the contour line is formed to be convex, while the curvature of the contour line is referred to as a negative curvature when the contour line is formed to be concave, a negative curvature portion where the curvature of the contour line becomes negative is provided on the runner side vane surface. The negative curvature portion is formed from an upper end portion to a lower end portion of the runner side vane surface.