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numerical investigation of inter-blade cavitation vortex for a Francis turbine at part load conditions

IET RENEWABLE POWER GENERATION 2021年第6期15卷 1163-1177页

作者： Sun, Longgang Guo, Pengcheng Luo, Xingqi Xian Univ Technol State Key Lab Ecohydraul Northwest Arid Reg 5 South Jinhua Rd Xian Peoples R China

Inter-blade cavitation vortex at part load has raised significant concerns about operation stability for Francis turbines due to tremendous development and integration of renewable energy resources into power grid. The principal objective of this study is to investigate the flow characteristics of inter-blade cavitation vortex and its influence on pressure fluctuations for a low-head Francis model turbine. Unsteady numerical simulations are carried out using shear stress transport turbulence model and Zwart cavitation model. numerical results yield to a good validation with the experimental data. The findings show that inter-blade cavitation vortices highlighted by cavitation structure and vortex structure are extremely different at the points adjacent to the incipient line of inter-blade cavitation vortex. The location of inter-blade cavitation vortex development in the runner is more sensitive to rotating speed than that to guide vane opening. The formation mechanism of inter-blade cavitation vortex is attributed to flow separation in the vicinity of the runner hub. Pressure fluctuations induced by inter-blade cavitation vortex are directly associated with the evolution of vapour volume in the runner and feature wide-band and low-frequency characteristic, and the fluctuations on the suction side of the runner blade are significantly magnified because of the presence of inter-blade cavitation vortex.

关键词： vortices unsteady numerical simulations blades Mechanical components computational fluid dynamics cavitation Francis turbine flow separation numerical approximation and analysis inter-blade cavitation vortex development Applied fluid mechanics flow simulation shear turbulence pressure fluctuations Power and plant engineering (mechanical engineering) hydraulic turbines Cavitation Fluid mechanics and aerodynamics (mechanical engineering) shear stress transport turbulence model General fluid dynamics theory, simulation and other computational methods Boundary layer and shear turbulence turbines numerical analysis vapour volume vortex structure numerical analysis Rotational flow, vortices, buoyancy and other flows involving body forces

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Design of metallic nanocylinder array waveguide for controlling resonant wavelength shift

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ELECTRONICS LETTERS 2021年第19期57卷 741-743页

作者： Ando, Yuki Endo, Motohiro Wu, Di Yamaguchi, Takashi Kishimoto, Seiya Ohnuki, Shinichiro Nihon Univ Coll Sci & Technol Dept Elect Engn Tokyo Japan Tokyo Metropolitan Ind Technol Res Inst Coll Sci & Technol Dept Elect Engn Tokyo Japan

A metallic nanocylinder array was previously proposed for the propagation of localized light generated in nanosized objects. However, the plasmon resonant wavelength for each cylinder shifts significantly with the propagation of light. In this study, a metallic nanoelliptic cylinder waveguide is investigated to control the plasmon resonant wavelength shift. The finite-difference frequency-domain (FDFD) electromagnetic solver is used to reduce the computational time. The relationship between the cross-section of the cylinder and the plasmon resonance for the metal is described with the hydrodynamic Drude model. The effectiveness of the proposed waveguide in controlling the resonant wavelength shifts is confirmed by examining the plasmon propagation for 30 nanocylinders.

关键词： numerical approximation and analysis Optical waveguides and couplers Structure of solid clusters, nanoparticles, nanotubes and nanostructured materials Collective excitations (surface states) Optical materials Optical waveguides Nanophotonic devices and technology

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Optimized design of a novel yokeless mover permanent magnet linear generator for free-piston stirling engines applied to solar cogeneration systems

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IET RENEWABLE POWER GENERATION 2021年第15期15卷 3631-3644页

作者： Tajdiny, Arman Monsef, Hassan Lessani, Hamid Univ Tehran Ctr Excellence Appl Electromagnet Syst Sch Elect & Comp Engn Coll Engn Tehran *** Iran

Considering the growing environmental issues, the use of renewable energy converters such as solar cogeneration systems has received more attention during recent years. Solar cogeneration systems convert the thermal energy of solar radiation into mechanical energy (by means of a free-piston Stirling engine) and then into electrical energy (by means of a linear generator). This paper introduces the novel yokeless mover permanent magnet linear generator (YMPMLG) to reduce mover mass, increase power density, increase thrust and decrease the normal force on the mover, which can make this generator a more suitable structure for operating in solar cogeneration systems. This paper is initiated with a comparative study of a YMPMLG with two reported prototypes in this field. Three generators with similar characteristics are simulated by the finite element method (FEM). The magnetic field flux density, power density, thrust coefficient, normal force, and efficiency parameters are analysed and compared in three generators. Following that, some dimensional parameters of the YMPMLG, including generator diameter and length and permanent magnet dimensions are optimized to achieve the highest possible power density and thrust coefficient using the 'hybrid genetic and pattern search' algorithm. The highest power density and efficiency are 0.58 kW/kg and 90.3%, respectively. In the end, the YMPMLG prototype has been tested to validate the results of the FEM method.

关键词： numerical approximation and analysis a.c. machines Synchronous machines d.c. machines Linear machines Optimisation techniques Control of electric power systems numerical analysis Mechanical components Optimisation techniques Finite element analysis

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Effects of sampling frequency on the proper orthogonal decomposition based reconstruction of a wind turbine wake

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IET RENEWABLE POWER GENERATION 2021年第13期15卷 2956-2970页

作者： Wang, Yan Wang, Liang Hu, RuiFeng Kong, LingXuan Cheng, Jie Lanzhou Univ Technol Sch Energy & Power Engn 287 Langongping Rd Lanzhou Peoples R China Lanzhou Univ Coll Civil Engn & Mech Ctr Particle Laden Turbulence Key Lab Mech Environm & Disaster Western China 222 TianShui Rd Lanzhou Peoples R China Lanzhou Univ Technol Key Lab Fluid Machinery & Syst Gansu Prov 287 Langongping Rd Lanzhou Peoples R China

The effects of sampling frequency on the efficacy of the POD technique for reconstructing the flow field of a wind turbine wake are studied in a neutral atmospheric boundary layer (ABL) using large eddy simulations (LES) coupled with an actuator disk model. The objective of this paper is to study how the sampling frequency over a fixed period of time affects the POD modes. The results showed that sampling frequency has little influence on the convergence of POD modes and the extraction of large-scale coherent structures. Meanwhile, sampling frequency has negligible influence on the kinetic energy contained in each mode of the first 25 modes. When the mode number is greater than 25, it affects the distributed energy in each mode and the accumulative energy in a given number of modes, and the accuracy of the reconstructed flow field. In present study, the flow field reconstructed using the smallest sampling frequency can be as accurate as that with the largest sampling frequency, while the former can save about 86% of the computational cost. For a given number of POD modes, a smaller sampling frequency may lead to more accurate flow field reconstruction. The sampling frequency mainly affects the small-scale structures.

关键词： Probability theory, stochastic processes, and statistics numerical approximation and analysis General fluid dynamics theory, simulation and other computational methods Applied fluid mechanics Wind power plants Fluid mechanics and aerodynamics (mechanical engineering) Mechanical components

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Investigation of novel thermoelectric sensor array configurations operating under non-uniform temperature distribution conditions for the measurement of maximum output power in an energy harvesting system

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IET SCIENCE MEASUREMENT & TECHNOLOGY 2021年第5期15卷 446-458页

作者： Thankakan, Rakesh Samuel Nadar, Edward Rajan Mepco Schlenk Engn Coll Autonomous Dept Elect & Elect Engn Sivakasi 626005 Tamil Nadu India

This research work proposes a configuration study of thermoelectric module (TEM) sensor array operating under uniform and non-uniform temperature distribution (NUTD) conditions. The four different (10 x 10) TEM array configurations, which are electrically connected in series-parallel (SP), all-tied (AT), bridge-joint (BJ), and bee-hive (BH), are considered to evaluate its performance under six cases of NUTD conditions. The electrical characteristics of the various sensor array configurations has been analysed and tested under both temperature distribution conditions using MATLAB-Simulink. A comparison of results of the various configurations is carried out in terms of maximum output power, voltage and current corresponding to maximum power, utilization factor, losses, relative error, standard deviation, and root mean square error. The maximum output power obtained from various cases of NUTD conditions confirm that the performance of bridge-joint configuration is best than all other configurations in the field of thermoelectric energy harvesting systems.

关键词： numerical approximation and analysis Sensing and detecting devices Thermometry Electrical instruments and techniques Computerised instrumentation Sensing devices and transducers Thermal variables measurement Transducers and sensing devices Computerised instrumentation Interpolation and function approximation (numerical analysis) Power and energy measurement Energy harvesting Energy harvesting

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Quasi-3D magnetic field simulation of superconducting devices with translational symmetry

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IET SCIENCE MEASUREMENT & TECHNOLOGY 2021年第3期15卷 319-327页

作者： D'Angelo, Laura A. M. De Gersem, Herbert Tech Univ Darmstadt Inst Accelerator Sci & Electromagnet Fields TEMF D-64289 Darmstadt Germany Tech Univ Darmstadt Ctr Computat Engn Darmstadt Germany

This work presents a quasi-three-dimensional (Q3D) approach for the magnetic field simulation in superconducting devices. First-order two-dimensional finite-element edge functions in the model's cross-section are combined with one-dimensional orthogonal polynomials along the longitudinal direction. The interfilament coupling currents arising in superconducting multi-filament materials are modelled by taking the associated magnetization into account. For this formulation, the Q3D ansatz is elaborated, verificated and applied to a superconducting cable model. In the end, the approach is compared to a conventional three-dimensional finite-element method against which the proposed Q3D method demonstrates a superior computational efficiency.

关键词： Algebra, set theory, and graph theory numerical approximation and analysis Steady-state electromagnetic fields electromagnetic induction Other superconducting devices and material applications

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Non-local effect on the frequency analysis of chiral single-walled carbon nanotubes using wave propagation approach

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MICRO & NANO LETTERS 2021年第9期16卷 469-477页

作者： Hussain, Muzamal Khadimallah, Mohamed A. Naeem, Muhammad Nawaz Govt Coll Univ Faisalabad Dept Math Faisalabad 38000 Pakistan Prince Sattam Bin Abdulaziz Univ Coll Engn Civil Engn Dept Al Khari 16273 Saudi Arabia

In the current study, the non-local elasticity theory is utilized for the vibration analysis of single-walled carbon nanotubes (SWCNTs). Frequency spectra have been demonstrated for different non-local parameters and bending rigidity for three sort of SWCNTs. It has been investigated that, by increasing the non-local parameter, frequencies decreases. The frequencies increase on increasing the aspect ratio. Throughout, the computation frequencies of clamped-free are lower than that of clamped-clamped. On increasing the bending rigidity, frequencies of chiral SWCNTs increase. Subsequently, the validation study has been performed through the available published literature. To discretize the governing equations of these models into frequency equations of SWCNTs, wave propagation approach is used. The complex exponential form with the number of axial modes depends on the boundary conditions indicated at the edges of the carbon nanotubes.

关键词： frequencies increase wave propagation Elasticity, elastic constants chiral SWCNTs increase wave propagation approach frequency spectra chiral single-walled carbon nanotubes numerical approximation and analysis frequency analysis shear modulus aspect ratio chirality nonlocal effect computation frequencies Structure of fullerenes and fullerene-related materials clamped-clamped different nonlocal parameters frequency equations vibration analysis elasticity frequencies decreases Elasticity and anelasticity carbon nanotubes bending rigidity nonlocal parameter bending nonlocal elasticity theory vibrations

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Piezoelectric energy harvester converting wind aerodynamic energy into electrical energy for microelectronic application

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IET RENEWABLE POWER GENERATION 2021年第9期15卷 1968-1975页

作者： Sitharthan, R. Yuvaraj, S. Padmanabhan, Sanjeevikumar Holm-Nielsen, Jens Bo Sujith, M. Rajesh, M. Prabaharan, N. Vengatesan, K. Vellore Inst Technol Sch Elect Engn Dept Elect Engn Vellore 632014 Tamil Nadu India SRM Inst Sci & Technol Dept Elect & Commun Engn Chennai Tamil Nadu India Aalborg Univ Dept Energy Technol Ctr Bioenergy & Green Engn Esbjerg Denmark IFET Coll Engn Dept Elect & Elect Engn Villupuram India Sanjivani Coll Engn Dept Comp Sci Engn Kopargaon India SASTRA Deemed Univ Sch Elect & Elect Engn Thanjavur Tamil Nadu India

Piezoelectric Energy Harvesting Systems play a vital role in energizing microelectronic devices with the low-frequency operation. Here, a novel piezoelectric energy harvesting device has been developed for low power electronic devices. The developed Piezoelectric Energy Harvesting Systems consists of a cantilever with poles projecting outwards and the cantilevers one end is connected to the wind-catcher, and another end is connected to the torsional spring. The developed Piezoelectric Energy Harvesting Systems signifies its application in energizing microelectronic devices. The cantilever is placed inwards to the piezoelectric crystal stack. When the wind strikes, a vortex is created in the windcatcher, which oscillates the cantilever and generates stress in the piezoelectric crystal stack to develop electric energy. The output voltage obtained from the Piezoelectric Energy Harvesting Systems does not affect any input frequency of the piezoelectric crystal. The result obtained shows that the developed Piezoelectric Energy Harvesting Systems generates 120-200 eV with 2.9 x 10(16)-4.84 x 10(16) Hz frequency considering an elementary charge unit as 40 for a variable wind flow of 4-9 m/s. This research aims to develop an efficient wind-based Piezoelectric Energy Harvesting Systems for low powered microelectronic devices.

关键词： numerical approximation and analysis Piezoelectric devices Energy harvesting

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Theoretical and experimental investigation of a novel point-focus Fresnel collector system with a novel receiver

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IET RENEWABLE POWER GENERATION 2021年第15期15卷 3622-3630页

作者： El-Leathy, Abdelrahman Al-Ansary, Hany Ba-abbad, Mazen Danish, Syed Noman AlShehri, Yazid Rizvi, Arslan Abbas King Saud Univ Mech Engn Dept POB 800 Riyadh 11421 Saudi Arabia Helwan Univ Mech Power Engn Dept Fac Engn Cairo 11718 Egypt King Abdulaziz City Sci & Technol Riyadh Saudi Arabia King Saud Univ Sustainable Energy Technol Ctr POB 800 Riyadh 11421 Saudi Arabia KA CARE Energy Res & Innovat Ctr Riyadh Saudi Arabia Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China

Here, experimental results for testing a novel solar concentrating system are presented. The novel receiver is tested on a technology that combines the two proven concepts of solar concentrating technologies (linear Fresnel reflector (LFR) and central receiver technologies) into a new concept called focal point Fresnel collector (PFFC) with a polar sun-tracking system. The PFFC system works by concentrating direct solar irradiation using several flat mirrors positioned over a square-rotating surface that follows the sun. Considering the solar elevation, the reflection is achieved using the Fresnel reflection concept. Rectangular mirrors of LFR technology are discretised into small square mirrors to achieve point focusing. A concentration ratio of 600 has been achieved, which is like that of parabolic dish (PD) systems. Mathematical modelling of the system is presented along with the experimental results. Furthermore, the PFFC system with the novel receiver provides similar thermal efficiency with comparatively higher manufacturing ease than the PD system. Besides, a maximum thermal efficiency of 87% has been achieved.

关键词： numerical approximation and analysis Optical lenses and mirrors Solar collectors, concentrators and control films: optical aspects Solar power stations and photovoltaic power systems Other direct energy conversion

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Theoretical and experimental research to development of water-film cooling system for commercial photovoltaic modules

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IET RENEWABLE POWER GENERATION 2021年第1期15卷 206-224页

作者： da Silva, Vinicius Oliveira Martinez-Bolanos, Julio Romel Heideier, Raphael Bertrand Gimenes, Andre Luiz Veiga Udaeta, Miguel Edgar Morales Saidel, Marco Antonio Univ Sao Paulo Polytech Sch Energy Grp Dept Energy & Elect Automat Engn Ave Prof Luciano GualbertoTravessa 3 Sao Paulo Brazil

This work aims at developing and validating mathematical models and empirically evaluating a water-film cooling system for commercial photovoltaic modules. Methodologically, thermal, electrical and climatological data measured in a specific purpose on-grid outdoor test unit were used. In this work they are used to study the improvement in the performance of photovoltaic energy production due to temperature reduction. The first-order state-space linear parametric model presents the best performance to predict the temperature of the uncooled photovoltaic modules, with normalised mean square error (NRMSE) of 86.75%. In contrast, the non-linear model performance of cooled photovoltaic modules is lower, with NRMSE of 44.5%;however, the results show that the performance of the complete thermoelectric model is satisfactory, with NRMSE of 76.38%. On the other hand, empirical tests showed that the cooling system reduces temperature in 15-19%, on average, and to a maximum of 35%. In terms of power, there are average gains of 5-9%, and maximum gains of 12%. Regarding gross generation, there are average gains of 2.3-6%, and maximum gains of 12%. It was concluded that it is possible to mathematically model and predict this generation using non-linear models with a 0.2% error between modelled and measured generation.

关键词： numerical approximation and analysis Photoelectric conversion solar cells and arrays Mathematical analysis Solar power stations and photovoltaic power systems Interpolation and function approximation (numerical analysis) Solar cells and arrays

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