Lecture notes in mechanical engineering, Год журнала: 2024, Номер unknown, С. 579 - 591
Опубликована: Янв. 1, 2024
Язык: Английский
Applied Energy, Год журнала: 2024, Номер 360, С. 122843 - 122843
Опубликована: Фев. 15, 2024
Язык: Английский
Процитировано
16
Energy, Год журнала: 2024, Номер 292, С. 130514 - 130514
Опубликована: Янв. 30, 2024
Язык: Английский
Процитировано
11
Physics of Fluids, Год журнала: 2024, Номер 36(2)
Опубликована: Фев. 1, 2024
The runaway process in hydraulic turbines is characterized by unstable flow that results the formation of vortex structures, pressure fluctuations, and energy dissipation. This study focuses on unsteady characteristics a Francis turbine during using numerical simulations. obtained speed discharge align well with experimental results. findings reveal larger openings lead to more rapid attainment speed. During process, extensive separation at runner blade generates columnar vortex, which obstructs channel dissipates energy. High-amplitude frequency below 0.5 times frequency, are observed passage components. These fluctuations attributed forming structure hub sheet band trailing edge blade. A large opening leads an earlier occurrence high-amplitude gradual increase amplitude low-frequency intense force runner. An analysis dissipation balance equation reveals turbulence plays dominant role transfer process. Additionally, caused induced presence edge. Furthermore, observe conversion within intensify increasing guide vane opening.
Язык: Английский
Процитировано
7
Physics of Fluids, Год журнала: 2023, Номер 35(8)
Опубликована: Авг. 1, 2023
Pressure fluctuations in the draft tube mainly arise from rotational motion of vortex rope. The formation and development rope are significantly influenced by cavitation. However, precise mechanism underlying progression cavitation its initial weak state to a more severe level remains unclear. objective this study is investigate pump-turbine operating under part load turbine conditions. Numerical simulations were conducted analyze impact coefficient on various parameters, including vapor volume, efficiency, head. With increasing degree cavitation, rope's pattern undergoes transition helical type torch-like type. This consequently leads shift dominant frequency pressure within tube. Furthermore, exhibits higher speed compared rope, thereby causing pronounced effect field. factors contributing morphological explored, with particular emphasis accelerating reverse axial flow reduction tube's circumferential velocity. Additionally, examined swirl number pattern, while also assessing entropy production. These findings provide valuable insight into control pump-turbines Moreover, they carry significant implications for design optimization systems.
Язык: Английский
Процитировано
14
Engineering Applications of Computational Fluid Mechanics, Год журнала: 2024, Номер 18(1)
Опубликована: Фев. 2, 2024
Francis turbines, essential for stability in diverse operating conditions and variable-speed scenarios, encounter efficiency-compromising vortex rope formations the draft tube, leading to substantial pressure fluctuations. This research delves into analysis of energy loss fluctuations associated with these ropes. Employing local entropy generation rate (LEGR) method chaos theory, we scrutinize behaviour ropes their resultant Notably, exhibit maximum LEGR near runner cone, secondary vortices escalating instability downstream. In elbow section, collision outer amplifies LEGR, primarily driven by fluctuating velocities (approximately 90%). Leveraging GWO-VMD algorithm, non-stationary signals are decomposed, unveiling a significant 1.6 Hz frequency under partial load (PL) isolating external noise frequencies, such as prominent 300 Hz. Following decomposition, theory tools, including phase space reconstruction trajectory graphs, unveil chaotic nature PL attributed spiral ropes, resulting profound study enhances our understanding systems provides methodologies improved reduction optimization turbine performance.
Язык: Английский
Процитировано
6
Physics of Fluids, Год журнала: 2024, Номер 36(2)
Опубликована: Фев. 1, 2024
Draft tube flow instability encountered under off-design operating conditions in hydraulic turbines significantly limits their operational flexibility. The arises consequent to a higher than threshold swirl content the runner outflow and leads vortex breakdown phenomenon draft cone. At high load condition, presents as an enlarged core counter-rotating with respect runner. situation is known compromise turbine efficiency besides generation of unwanted effects such power swings large-scale pressure fluctuations. present paper first encapsulate thorough numerical investigation on formation evolution alongside effects. A transient sequence between best points model Francis simulated. Turbulence closure has been attained using shear stress transport-scale adaptive simulations turbulence model. Dynamic meshing based Laplacian smoothing scheme used account for mesh deformation arising from guide vane motion during change. velocity fields have determined analyzed elucidate physics breakdown, underlying core. Furthermore, fluctuations at salient domain Fourier short-time transforms. Finally, formed visualized through λ2 criterion. takes shape cork-screw like compactly wound spiral structure extending up elbow.
Язык: Английский
Процитировано
4
Physics of Fluids, Год журнала: 2024, Номер 36(3)
Опубликована: Март 1, 2024
The presented paper numerically investigates the internal flow behaviors and energy dissipation during no-load startup process toward a Francis turbine. Passive runner rotation is implemented through angular momentum balance equation accompanied by dynamic mesh technology user defined function. Three phases of rotational speed are identified: stationary, rapid increase, slow increase. Head exhibits monotonic decrease, rise fall, eventual fluctuation. Flow rate shows quasi-linear pressure fluctuations in vaneless region primarily dominated frequencies induced Rotor-Stator Interaction broad frequency range below 50 Hz, 30 Hz draft tube. Runner inlet experiences positive to negative incidence angles, causing intense separation unstable structures. Draft tube large-scale recirculation evolving vortex Energy loss analysis based on entropy production method highlights as primary contributors. within an initial subsequent then again stationary increase phases. While phase Turbulent significantly contribute loss, with trends matching total production. Maximum locations correspond wall, emphasizing importance generation. This study establishes foundational insights into hydrodynamics modes hydraulic turbine startup, paving way for further research.
Язык: Английский
Процитировано
3
Lecture notes in mechanical engineering, Год журнала: 2025, Номер unknown, С. 23 - 32
Опубликована: Янв. 1, 2025
Процитировано
0
Engineering Applications of Computational Fluid Mechanics, Год журнала: 2025, Номер 19(1)
Опубликована: Фев. 12, 2025
Язык: Английский
Процитировано
0
Energy, Год журнала: 2025, Номер 320, С. 135399 - 135399
Опубликована: Март 1, 2025
Язык: Английский
Процитировано
0