Analysis of Internal Flow Characteristics of a Startup Pump Turbine at the Lowest Head under No-Load Conditions

Abstract

The instability of the no-load working condition of the pump turbine directly affects the grid connection of the unit, and will cause vibration and damage to the components of the unit in severe cases. In this paper, a three-dimensional full flow numerical model including the runner gap and the pressure-balance pipe was established. The method SST k-ω model was used to predict the internal flow characteristics of the pump turbine. The pressure pulsation of the runner under different operating conditions during the no-load process was compared. Because the rotation speed, flow rate, and guide vane opening of the unit change in a small range during the no-load process, the pressure pulsation characteristics of the runner are basically the same. Therefore, a working condition was selected to analyze the transient characteristics of the flow field, and it was found that there was a high-speed ring in the vaneless zone, and a stable channel vortex was generated in the runner flow passage. Analyzing the axial water thrust of each part of the runner, it was found that the axial water thrust of the runner gap was much larger than the axial water thrust of the runner blades, and it changed with time periodically. It was affected by rotor stator interaction. The main frequency was expressed as a multiple of the number of guide vanes, that is, vanes passing frequency, 22fn. During the entire no-load process, the axial water thrust of the runner changed slowly with time and fluctuated slightly.

Research on the Flow-Induced Stress Characteristics of Head-Cover Bolts of a Pump-Turbine during Turbine Start-Up

“…Since the model tests and prototype tests of large hydraulic turbines are usually very expensive and time-consuming, scientific numerical simulation becomes an alternative method to investigate the fluid dynamics and the structural dynamics of the turbine units. Many researchers [25][26][27][28][29][30][31][32][33] have verified the reliability of numerical calculations of hydraulic turbines by comparing the calculated results with the measured ones. Several studies [34][35][36] have used the dynamic mesh technique to simulate the unsteady flow of PT units in transient processes, and the simulation results were in good agreement with the experimental ones.…”

“…However, a transient process calculation took months even with many computational resources, which could not provide fast feedback to the PT designers of real engineering projects within a given time frame. For this reason, some scholars [26,27,[37][38][39] have proposed a simplified method to calculate the fluid flow at each critical moment of transient processes and to study the flow-induced stresses of PT structures. This calculation method requires substantially less time and computational resources, and the simulation results agree well with corresponding measured ones.…”

“…The PT unit has 22 stay vanes, 22 guide vanes, and 13 runner blades, and the runner diameter is 4.6 m. The boundary conditions at the spiral case inlet and draft tube outlet were set as total pressure inlet and static pressure outlet, respectively. The other surfaces were set as noslip walls [25,26]. The SST k-ω turbulence model, which effectively blends the k-ω and k-ε models, was used to perform the fluid dynamic calculations.…”

“…The k-ω model is used to simulate the flow near the wall, while the k-ε model is used for the flow away from the wall. It gives highly accurate predictions of the onset and the amount of flow separation under adverse pressure gradients [26,27,44]. The spiral case, stay vane, guide vane, pressure-balance The SST k-ω turbulence model, which effectively blends the k-ω and k-ε models, was used to perform the fluid dynamic calculations.…”

“…In previous studies, we have calibrated the finite volume mesh with the test results [26]. As shown in Figure 3, a combination of tetrahedral and hexahedral mesh was established for the entire flow field of the PT unit.…”