Abstract
The vortex rope in the draft tube is considered as the major contributor to pressure pulsation at partial load (PL) conditions, which causes the hydro unit to operate unstably. Based on the prototype Francis turbine HLA551-LJ-43 in the laboratory, J-grooves are designed on its conical section in this paper. We used numerical simulation to study the effect of the J-grooves on vortex suppression and energy dissipation in the draft tube. Four typical operating conditions were chosen to analyze the vortex suppression; the corresponding flow ratios Q* are 100%, 82%, 69%, and 53%, respectively. Entropy production theory is used to calculate the energy losses and assess the effect of the J-groove on energy dissipation under part-load conditions. By comparing entropy production, circumferential and axial velocity components, swirl intensity, pressure pulsation, and vortex distribution in a draft tube with and without J-grooves at different operating conditions, it can be concluded that the entropy production on the wall containing a conical section with J-grooves is obviously smaller than that without J-grooves, the effects of J-grooves on reducing circumferential velocity component Vu, pressure pulsation, and weakening vortex intensity and vortex rope in the conical section are obvious, especially at part load and deep part-load operating conditions. Using J-grooves shows better performance on vortex control and energy dissipation in the draft tube of a Francis turbine at partial load conditions.
Highlights
Hydropower, the only green energy with mature technology that can be used at a large scale, has an important role in power systems, where its safe and stable operation is essential
Compared with the traditional analysis approach of pressure and velocity fields, the unstable operation andisreduced efficiency of the turbine caused by pressure flu entropy production method more intuitive to analyze energy dissipation, which helps and energy losswhere are discussed at losses the four typical operating poin toswirl betterintensity, know the accurate location the hydraulic occur and understand the flow. the
The Q* = 53% operating condition was chosen to evaluate the effect on the eddy current changes and flow characteristics at different operation co of the J-grooves on reducing the energy losses of the unit and analyze the performance of with or without
Summary
Hydropower, the only green energy with mature technology that can be used at a large scale, has an important role in power systems, where its safe and stable operation is essential. Francis turbines often perform peak and frequency modulation tasks in the system, such that the units inevitably operate under partial load (PL) conditions and produce evident pressure pulsation when they deviate from the design flow condition. Different degrees of vortex occur in the conical section of the draft tube, especially at 0.4 to 0.8 times the design flow, which induces pressure pulsation. Pressure pulsation can cause the output efficiency to fluctuate, resulting in the resonance of hydro units and powerhouses, which seriously affects the safety of the hydro units and powerhouses; how to suppress the pressure pulsation in the draft tube under partial load conditions effectively has become an important issue. In order to increase the operation stability of the hydro unit, researchers have been looking for a simple and easy measure to suppress the pressure pulsation in the draft tube at PL conditions
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