Investigations into Hydraulic Instability during the Start-Up Process of a Pump-Turbine under Low-Head Conditions
Abstract
:1. Introduction
2. Computational Model and Numerical Simulation Setup Methods
2.1. Full-Flow System Model of a Pumped Storage Power Station
2.2. Grid Partitioning and Grid Independence Verification
2.3. Boundary Conditions and Numerical Solution Method
2.4. Start-Up Implementation Methods
2.4.1. Moment Balance Equation
2.4.2. Moving Grid Technique
2.5. Setting of Pressure Monitoring Points
3. Results and Discussion
3.1. Numerical Simulation Validation
3.2. Analysis of the Unit’s External Characteristics
3.3. Analysis of Unit Pressure Pulsation Characteristics
3.3.1. Analysis of Pressure Pulsations in the Guide Vane and Runner Areas
3.3.2. Pressure Pulsation Characteristics in the Draft Tube Region
3.4. Analysis of Internal Flow Characteristics
3.4.1. Analysis of Guide Vane and Runner Flow Characteristics
3.4.2. Analysis of Flow Characteristics in the Draft Tube
4. Conclusions
- (1)
- During the low-head start-up process of the pump-turbine unit, in the phase of guide vane opening, flow vortical structures emerged, blocking flow passages specifically at the runner inlet, within the runner inter-blade channels, and at the draft tube inlet. This led to a decrease in flow rate and the generation of the water hammer effect, causing a rapid increase in pressure upstream of the runner. After the reduction of high-pressure due to the water hammer, the flow rate rapidly increased, causing a small negative water hammer and resulting in significant fluctuations in the head of the unit.
- (2)
- After the guide vanes stopped moving, the intensity of vortex structures at the runner inlet and outlet decreased. As the torque of the runner continued to decrease, the unit entered the S-shaped region and approached the no-load condition, leading to an enhancement of pressure pulsation. In addition, unstable vortex structures reappeared at the leading and trailing edges of the runner blades.
- (3)
- During the start-up process of the pump-turbine unit, unstable vortex structures formed in the draft tube region, at the intersection of the inflow along the wall of the tapered section and the backflow along the centerline of the draft tube. At the stage of increasing runner torque, as the flow worked on the runner, the rotational speed of the runner increased while the inflow velocity in the draft tube remained constant. The increased work on the suction side of the runner led to the extension of vortex structures from the center position of the tapered section downstream. At the stage of decreasing runner torque, the inflow velocity in the draft tube increased, and the vortex structures in the draft tube evolved into a double-layered structure near the center and near the wall, respectively. This vortex structure is also the source of low-frequency pressure pulsation in the draft tube and the instability of the unit under no-load conditions.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Present Work | Existing State-of-the-Art | |
---|---|---|
Numerical simulation method | Three-dimensional model (3D) | 3D and 1D–3D coupled methods |
Main research content | Research on the instability and its mechanisms during the start-up process in low-head condition | Primarily focuses on the unit’s flow characteristics. |
Analytical methods | Analyze the internal flow state using a combination of entropy production theory and vortex identification methods. | Only the external characteristics are analyzed, with less attention given to the relationship between internal flow states and changes in external characteristics. |
Conclusion | Explain the mechanisms of changes in external characteristics and pressure pulsation characteristics during the startup process and identify the causes of hydraulic instability in pump storage units at low-head conditions during start-up. | Existing literature addresses this aspect only briefly. |
Parameters | Value |
---|---|
Normal upper reservoir water level | 716.0 m |
Upper reservoir dead water level | 691.0 m |
Normal lower reservoir water level | 299.0 m |
Lower reservoir dead water level | 262.0 m |
Pump-turbine model | HLNA1518-LJ-412 |
Rated output under turbine operating conditions | 306.1 MW |
Maximum input under pump operating conditions | ≤325 MW |
Rated speed | 428.6 r/min |
Rotational inertia of generator | 6000 t·m2 |
Rotational inertia of pump-turbine | 240 t·m2 |
Guide vane centerline elevation | 192.0 m |
Number of runner blades | 9 |
Number of guide vanes | 20 |
Number of stay vanes | 20 |
Flow Components | Number of Nodes/104 |
---|---|
Upstream penstock | 68.8 |
Spiral case | 104.2 |
Stay vanes | 52.7 |
Guide vanes | 136.5 |
Runner | 182.3 |
Draft tube | 86.5 |
Downstream penstock | 69.0 |
Total | 700.0 |
Parameters | φ = H (m) | φ = M (kN·m) |
---|---|---|
Number of grids N1 | 700 | |
Number of grids N2 | 591 | |
Number of grids N3 | 496 | |
Grid refinement factor r21 | 1.06 | |
Grid refinement factor r32 | 1.06 | |
Numerical solution φ1 | 390 | 5476 |
Numerical solution φ2 | 387.5 | 5445 |
Numerical solution φ3 | 384 | 5400 |
Safety factor Fs | 1.25 | 1.25 |
Convergence accuracy p | 5.77 | 6.4 |
Grid convergence index GCI21 | 2.00% | 1.57% |
Grid convergence index GCI32 | 2.82% | 2.29% |
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Wang, T.; Yu, C.; Yang, H.; Zhao, Y.; Zhou, Y.; Liu, H.; Zhou, D.; Kan, K. Investigations into Hydraulic Instability during the Start-Up Process of a Pump-Turbine under Low-Head Conditions. Processes 2024, 12, 1876. https://doi.org/10.3390/pr12091876
Wang T, Yu C, Yang H, Zhao Y, Zhou Y, Liu H, Zhou D, Kan K. Investigations into Hydraulic Instability during the Start-Up Process of a Pump-Turbine under Low-Head Conditions. Processes. 2024; 12(9):1876. https://doi.org/10.3390/pr12091876
Chicago/Turabian StyleWang, Tingzheng, Chuqiao Yu, Haocheng Yang, Yilin Zhao, Yibo Zhou, Hanzhong Liu, Daqing Zhou, and Kan Kan. 2024. "Investigations into Hydraulic Instability during the Start-Up Process of a Pump-Turbine under Low-Head Conditions" Processes 12, no. 9: 1876. https://doi.org/10.3390/pr12091876