Francis Runner Vane Curvature for Transient Speed Stability
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Solution Overview
Problem
Conventional Francis runners struggle to stabilize rotation speed during transient phases, especially for small heads, leading to instability and inability to couple with the electrical network without additional coupling devices.
Innovation Solution
A Francis runner with a wheel and crown having inwardly curved vanes with a peripheral edge that is curved and concave, featuring a radius of the intermediate point smaller than the connection points, allowing stable operation for smaller heads and rapid network coupling without additional devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional Francis runners are used, then the structure is simple, but the rotation speed becomes unstable during transient phases for small heads
Solution Approach 1:
The patent applies curvature to the leading edge of the vanes, specifically making it hollowed or concave rather than straight. This curved geometry modifies the flow characteristics of water passing through the runner, stabilizing the rotation speed during transient phases and enabling operation at small heads without additional coupling devices. The curved leading edge creates a more favorable pressure distribution and reduces flow separation, thereby improving rotational stability.
2Ease of operation
If the distributor opens gradually during turbine starting, then the flow rate increases smoothly, but oscillations occur in the runner rotation speed
Solution Approach 1:
The hollowed leading edge of the vanes modifies how the runner responds to gradual distributor opening during starting. The curved geometry dampens flow-induced oscillations and promotes smoother acceleration, allowing the turbine to start without speed instability even as the distributor opens gradually.
3Reliability
If additional coupling devices are used to stabilize rotation speed, then the alternator can be coupled to the electrical network, but the device complexity increases
Solution Approach 1:
The patent extracts or removes the need for additional coupling devices by incorporating the stabilization function directly into the runner geometry. The hollowed leading edge of the vanes provides inherent rotational stability, eliminating the requirement for separate coupling mechanisms and simplifying the overall system while maintaining reliable network coupling capability.
Solution Approach 2:
The runner is designed to perform multiple functions: it converts hydraulic energy to mechanical energy while simultaneously providing rotation speed stabilization during transient phases. This multi-functionality integrates the coupling capability directly into the runner, eliminating the need for dedicated coupling devices.
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 unique geometry stabilizes rotation speed and enables quick coupling with the electrical network for small heads, reducing turbulence and instability, thus facilitating stable operation and eliminating the need for additional coupling devices.
Implementation Method 1
The unique geometry stabilizes rotation speed and enables quick coupling with the electrical network for small heads, reducing turbulence and instability
Implementation Method 2
installation for converting hydraulic power into electrical power comprises a hydraulic machine which operates in turbine mode and which is passed through by a forced flow of water
Implementation Method 3
The runner of the turbine drives in rotation a shaft connected to an alternator. In order to couple the alternator to the electrical network, the rotation speed of the turbine must be stable, in order for the frequency of the electrical signal at the output of the alternator to be equal to the frequency of the electrical network
Data Source
AI summary
The invention relates to a Francis runner (200) for a hydraulic machine, comprising: a wheel (1), which is rotationally symmetrical about an axis of rotation (Z) of the runner (200); a crown (12); and a plurality of inwardly curved vanes (21), each of which has a peripheral edge (212). The peripheral edge (212) of at least one of the vanes is curved, the concavity thereof facing toward the outside of the runner (200). The maximum value of the distance measured between any point on the peripheral edge (202) and a straight line passing through a first connection point between the peripheral edge (212) and the wheel (1), and through a second connection point between the peripheral edge (212) and the crown (12), is at an intermediate point on the peripheral edge (212). The radius (Rn) from the intermediate point (N) is strictly smaller than the radius (Ra) from the first connection point (A). The radius (Rn) from the intermediate point (N) is strictly smaller than the radius (Rc) from the second connection point (C).