Abstract
Nowadays, pump-turbine units have to experience multiple start-stops every day to balance the power production and consumption on the grid. During the transient process of turbine start-up, the hydraulic forces applied to the head-cover would change dramatically and induce high-level stresses on the head-cover bolts. As key components of large hydraulic turbine units, the head-cover bolts are subjected to tens of thousands of tonnes of hydraulic excitation force during operation. Special attention should be paid to the design of the head-cover bolts of large hydraulic pump-turbine units because these units have high water heads and high hydraulic excitation forces. Therefore, the safe design of the head-cover bolts is extremely important to maintain the operational safety of the whole unit. This paper investigates the flow-induced stress characteristics of the head-cover bolts during turbine start-up in a large prototype pump-turbine unit. A complete 3D fluid model and a corresponding 3D structural model, including the head-cover bolts of the pump-turbine unit, were created. The fluid–structure coupling method was used to calculate the structural stresses caused by fluid flow during turbine start-up. The pressure files during turbine start-up calculated by the CFD tool were transferred and mapped to the finite element model of the structural components of the pump-turbine unit. Subsequently, the flow-induced stress characteristics of the head-cover bolts were numerically simulated. The simulation results showed that the hydraulic excitation force on the head-cover bolts increased significantly during turbine start-up, and the displacement and the stress distributions of different head-cover bolts were not uniform. The calculation methods and conclusions in this paper can also be applied to evaluate the flow-induced stress characteristics of head-cover bolts for similar hydraulic pump-turbine units.
Highlights
This paper presents a detailed investigation of the flow-induced stress characteristics of the head-cover bolts in a large prototype reversible PT unit during turbine start-up
M HC g where FHC is the hydraulic forces acting on the head-cover calculated by the Computational fluid dynamics (CFD), m HC is the mass of the head-cover, and g is the gravitational acceleration, 9.8 m·s-2
The operating condition of pump-turbines is complicated because the machine has
Summary
With the global trend of low-carbon economy development and the growing demand for clean and renewable energy, hydropower has been further developed vigorously, especially in developing countries. In order to obtain a large energy storage capacity, PSPS usually has a high water head, which could generate hydraulic excitation forces of tens of thousands of tonnes on the structures of pump-turbine (PT) units. The reversible PT units in PSPSs have to be started and stopped more frequently each day to meet the ever-changing demands of the grid for power generation and energy storage. 1832to have be started and stopped more frequently each day to meet the ever-changing demands of the grid for power generation and energy storage. During turbine start-up, the hydraulic excitation forces acting on the head-cover and other PT structures change drastically, and the amplitude the acting excitation forces can alsoand reach tens thousands of drastically, and excitation of forces on the head-cover other
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