Francis Pump-Turbine Runner Blade Curved Trailing Edge
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Solution Overview
Problem
Francis pump-turbines face efficiency issues during partial load operations, with water flow rate deviations causing energy loss and backflow problems due to secondary flow and centrifugal forces, and existing solutions either worsen pump efficiency or fail to address turbine efficiency.
Innovation Solution
The design features runner blades with a curved trailing edge expanding towards the main shaft, a maximum point, and specific angle and distance ratios to reduce energy loss and prevent backflow, while maintaining efficient water distribution and reducing pressure differences between pressure and suction surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the curved portion connecting the crown-side end and band-side end of the trailing edge is shifted towards the main shaft to reduce secondary flow loss, then partial load efficiency is improved, but backflow occurs during pump operation, decreasing pump efficiency
Solution Approach 1:
The invention changes the geometric parameters of the trailing edge curved portion, specifically setting the angle α between 90° and 150° and the distance ratio Rc/Rb between 0.3 and 0.7. These parameter optimizations balance the reduction of secondary flow loss during turbine operation while preventing backflow during pump operation, resolving the efficiency trade-off between the two modes.
Solution Approach 2:
The invention introduces asymmetric design by defining specific angular and dimensional relationships for the trailing edge curved portion that differ from conventional symmetric designs. The asymmetric configuration of the curved portion connecting crown-side and band-side ends creates optimized flow patterns that simultaneously address both turbine and pump operation requirements.
2Ease of manufacture
If the runner blade trailing edge is designed with a straight line connection between crown-side and band-side ends, then manufacturing is simplified, but water flow drifts toward the band during partial load, causing significant efficiency loss
Solution Approach 1:
The invention replaces the straight line connection with a curved portion connecting the crown-side end and band-side end of the trailing edge. This curvature is specifically designed with angle α between 90° and 150° to redirect water flow away from the band during partial load turbine operation, reducing secondary flow loss while remaining manufacturable.
3Stability of the object's composition
If the curved portion of the trailing edge is expanded significantly towards the main shaft, then flow uniformity is improved, but the distance between the curved portion and main shaft becomes too small, inducing backflow during pump operation
Solution Approach 1:
The invention optimizes the distance ratio Rc/Rb between 0.3 and 0.7, where Rc is the distance from the main shaft to the crown-side end and Rb is the distance from the main shaft to the band-side end. This parameter range ensures sufficient flow uniformity while maintaining adequate clearance from the main shaft to prevent backflow during pump operation.
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 enhances partial load efficiency by minimizing energy loss and preventing backflow during pump operation, improving both turbine and pump efficiency by maintaining uniform water flow and increasing the wet area.
Implementation Method 1
the driving water is affected by a centrifugal force to drift toward the band 10
Implementation Method 2
When the flow rate of the water exceeds a design point, the water drifts toward the crown 9, causing a loss due to so-called secondary flow
Data Source
AI summary
A Francis pump-turbine includes a runner provided with runner blades arranged around in a circumferential direction of a main shaft of the runner, each of the runner blades being supported by a band at a bottom side thereof in a blade height direction and supported by a crown at a head side in the blade height direction, in which the runner blade is formed, at a trailing edge thereof, with a curved portion expanding to the main shaft when the turbine is in operation, the curved portion has a maximum point with respect to a straight line connecting a crown-side trailing edge connecting end at which the trailing edge and the crown are connected and a band-side trailing edge connecting end at which the trailing edge and the band are connected, and an angle α formed by a straight line connecting the maximum point and the crown-side trailing edge connecting end and a straight line connecting the maximum point and the band-side trailing edge connecting end is set to be within a range of α≦150°.