Numerical analysis of vorticity transport and energy dissipation of inner-blade vortex in Francis turbine

Tang, Qinghong; Yu, An; Wang, Yongshuai; Tang, Yibo; Wang, Yifu

doi:10.1016/j.renene.2022.12.086

Cited by 13 publications

(4 citation statements)

References 31 publications

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“…As can be seen from Figure 4, the hydraulic loss derived from the pressure-drop method is closer to the entropy production calculation results, with a maximum coefficient of error of 1.75% in Case 1, and with the flow rate increase the error is relatively reduced, with a minimum coefficient of variance of 0.73% in Case 3. The total calculation distributions of both show similarity, but because the entropy production method can quantitatively obtain the specific distribution of hydraulic losses and can estimate the energy loss caused by different hydraulic loss phenomena such as internal flow vortex [26,27], inverse gradient flow, and backflow, it has become an important means of evaluating the hydraulic efficiency of hydraulic machines at present [28,29]. Figure 5 shows the total internal hydraulic loss of the turbine under different operating conditions and the distribution of head loss at each structure.…”

Section: Total Hydraulic Loss Distribution Of the Turbinementioning

confidence: 99%

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Wang,

Zhou,

et al. 2023

Processes

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Hydraulic vibrations in Francis turbines caused by cavitation profoundly impact the overall hydraulic performance and operational stability. Therefore, to investigate the influence of cavitation phenomena under high-load conditions, a three-dimensional unsteady numerical simulation is carried out for a Francis turbine with different head operating conditions, which is combined with the SST k-w turbulence model and two-phase flow cavitation model to capture the evolution of cavitation under high-load conditions. Additionally, utilizing entropy production theory, the hydraulic losses of the Francis turbine during cavitation development are assessed. Contrary to the pressure-drop method, the entropy production theory can quantitatively reflect the characteristics of the local hydraulic loss distribution, with a calculated error coefficient τ not exceeding 2%. The specific findings include: the primary sources of energy loss inside the turbine are the airfoil cavitation and cavitation vortex rope, constituting 26% and 71% of the total hydraulic losses, respectively. According to the comparison with model tests, the vapor volume fraction (VVF) inside the draft tube fluctuates periodically under high-load conditions, causing low-frequency pressure pulsation in the turbine’s power, flow rate, and other external characteristic parameters at 0.37 Hz, and the runner radial force fluctuates at a frequency of 1.85 Hz.

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Section: Total Hydraulic Loss Distribution Of the Turbinementioning

confidence: 99%

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Wang,

Zhou,

et al. 2023

Processes

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“…The process of vortex incipient, growth, and shedding to complete dissipation induces various instability problems in the operation of turbomachinery, such as turbulent motion noise [5], rotational stall [6], and cavitation [7], which will eventually affect the regular operation of the system. Therefore, the accurate identification of vortex structures in fluid machinery is of great significance to mastering various unsteady flow structures and optimizing the flow process in turbomachinery [8]. In intuitive understanding, vortices are commonly associated with the rotational motion of fluids, but it is important to note that there is still much controversy in academia over the specific definition of vortices.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of vortex structure and unsteady evolution in multi-stage double-suction centrifugal pump

Zhao,

Pei,

Yuan

et al. 2024

J. Phys.: Conf. Ser.

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Multi-stage double-suction centrifugal pump is constructed to handle situations with large flow rates and high head. However, due to the complex internal flow structure, the pump can experience hydraulic excitation caused by the presence of numerous vortical structures. Such excitation can lead to unstable pump operation and increased energy losses. In this study, we aim to analyze the multi-stage double-suction centrifugal pump by combining numerical simulation using detached eddy simulation (DES) and experiments to accurately capture the vortical structure and elucidate the mechanism of the rotor-stator interaction (RSI) formation. The results indicate that the omega vortex identification method can accurately capture the vortex structure in the pump, irrespective of the threshold value and without the influence of wall shear layers. Additionally, based on this identification method, we have analyzed the unsteady evolution characteristics of the vortex structure in the pump. Specifically, we have focused on the shedding of wake vortices and their collision with the tongue. The findings suggest that the rotor-stator interaction primarily arises from the periodic shedding of wake vortices near the impeller outlet. In summary, this study provides valuable insights into the flow dynamics of multi-stage turbomachines.

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“…Reza et al studied the pressure fluctuation of large hydropower stations with Francis turbine units and found that the pressure fluctuation is significant at lower power levels, and many pressure waves caused by turbulence in the running unit waterway have a great impact on adjacent units [3]. Tang et al studied the Francis turbine inner vortex characteristics by using numerical methods [4]. Su et al studied the pressure pulsation characteristics of a Francis turbine under local flow conditions and concluded that chaotic attractors do exist in the turbine pressure fluctuation signal [5].…”

Section: Introductionmentioning

confidence: 99%

Study on the design of short blade offset for the long and short blade runner of 1000 MW hydraulic turbine units

Lu,

Zhang,

Chen

et al. 2024

J. Phys.: Conf. Ser.

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For such complex rotating machinery as hydraulic turbine, the hydraulic operation characteristics of the hydraulic turbine unit are significantly impacted by the short blade of the runner used as the splitter blade. To find the optimum position of the short blade, the study object is the 1000 MW hydraulic turbine, selects three circumferential offset positions of the short blade for numerical simulation calculation, obtains the runner flow pattern at different offsets, and explores the impact on the short blade offset on the vortex and pressure pulsation in the runner. The results show that the counterclockwise offset of the short blade will improve the flow pattern of the runner, reduce the scale of vortex in the runner and enhance the efficiency of the hydraulic turbine. The counterclockwise offset will increase the interference while decreasing the pressure pulsation in the vaneless region, at the runner’s inlet, and downstream of the short blade. When the offset δ=0.6, the peak-valley difference of pressure fluctuation in the vaneless zone is the smallest, accounting for only 1.38 % of the rated head. The main frequency of the vaneless zone gradually changes from 15fn to 30fn , and the main frequency of the runner inlet and the short blade downstream is 24fn . Due to the different weakening effects of short blades on the interference, low-frequency pulsation components of 4fn and 8fn appear.

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Numerical analysis of vorticity transport and energy dissipation of inner-blade vortex in Francis turbine

Cited by 13 publications

References 31 publications

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

Numerical investigation of vortex structure and unsteady evolution in multi-stage double-suction centrifugal pump

Study on the design of short blade offset for the long and short blade runner of 1000 MW hydraulic turbine units

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