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The worldwide consumption of pistachio nuts has been increasing over the last decades due to their high nutritional value. Given that only split nuts are commercialised, the closed-shell nuts, which account for most of the harvested ones, must be split by mechanical or thermal processes. However, there is hardly any information about the splitting mechanism based on thermal treatments. Accordingly, the thermal splitting of pistachio nuts in conical spouted beds has been approached, and the effect of the air inlet temperature, the draft tube aperture ratio and the air inlet diameter on the splitting mechanism has been analysed. Batch drying tests have been carried out in the proposed technology at an air inlet temperature range of 40–120 ∘ C using configurations with and without draft tube. The operating temperature and dryer configuration that allows attaining up to 60% of split pistachios and preserving their quality are 80 ∘ C , an inlet diameter of 0.05 m and an open-sided draft tube with an aperture ratio of 80%. [ABSTRACT FROM AUTHOR]

Under partial load operating conditions, vortex rope generation in the draft tube of a Francis turbine is considered one of the main reasons for hydro unit vibration. In this paper, a Francis turbine HLA551-LJ-43 in the laboratory was taken as a prototype. Numerical simulations of the entire flow passage were carried out. Four different hydro-turbines were chosen to analyze the effect of vortex suppression, which were named the prototype turbine (N-J), the turbine with J-grooves installed on its conical section (W-J), the one with extending runner cone (C), and the one that considered the J-grooves and the extending runner cone at the same time (J+C). Under the part load conditions in which the vortex rope is easily generated (0.4–0.8 times design flow QBEP), the spectrum characteristics of pressure fluctuation, the morphology of vortex rope, and the energy dissipation based on the entropy production theory in the draft tube were studied. The results show that the three optimized structures W-J, C, and J+C could reduce the pressure pulsation in the conical section of the draft tube, weaken the eccentricity of the vortex rope, and decrease the energy losses in the runner and draft tube. It is worth mentioning that the turbine with a J+C optimized structure had the most potent effect on vortex suppression and energy dissipation. Primarily when operating in deep partial load (DPL) conditions, the efficiency of the turbine with a J+C optimized structure was increased by 13.7% compared to the prototype turbine, and the main frequency amplitude of the pressure pulsation in the draft tube was reduced to 32% of the prototype. [ABSTRACT FROM AUTHOR]

Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The flow in the draft tube of the water turbine is affected by the upstream flow and the inherent structure accompanied by various undesirable characteristics, affecting the efficient and stable operation of the water turbine. Changing the flow structure downstream of the runner is an important measure to reduce hydraulic loss in the draft tube and improve stability. In this study, three downstream structures of the runner, namely, the non-locking nut, small locking nut, and extended locking nut are numerically calculated and verified using experimental results. The unstable flow characteristics of the draft tube are analyzed using variations in swirling flow, backflow, pressure gradient, and vortex strip. The results show the non-negligible effect of the locking nut, which significantly reduces the rotational momentum flux at the draft tube inlet, accelerates the decay rate of the swirling flow, and suppresses the generation of axial low pressure. The small locking nut significantly reduces the pressure gradient, shortens the backflow zone, and decreases the backflow velocity. The extended locking nut reduces the backflow zone in some sections and reduces the vortex zone of the straight section but prolongs the backflow zone and increases the backflow velocity. [ABSTRACT FROM AUTHOR]

With the increasing popularity of clean energy, the use of micro turbines to recover surplus energy in the water supply pipelines of high-rise buildings has attracted more attention. This study adopts a predictor model based on Radial Basis Function Neural Network (RBFNN) to optimize the draft tube shape for micro-Francis turbines. The predictor model is formed on a dataset provided by numerical simulations, which are validated by lab tests. Specifically, numerical investigations are carried out in the shape of a draft tube to determine an optimal model. Additionally, the superiority of the RBFNN model in nonlinear optimization is verified by comparing it with other models under the same date sets. After that, the design parameters are optimized using RBFNN and sequential quadratic programming algorithm (SQPA). Finally, the turbine prototype is fabricated and tested on a lab test rig. The experimental results indicate that the numerical method adopted in this research is accurate enough for such a micro-Francis turbine performance prediction. Under the design conditions, the proposed micro-Francis turbine produces a power of 147 W with an efficiency of over 29%, which shows a considerable improvement compared to the initial prototype. [ABSTRACT FROM AUTHOR]

This study aims to provide a comprehensive assessment of single-objective and multi-objective optimisation algorithms for the design of an elbow-type draft tube, as well as to introduce a computationally efficient optimisation workflow. The proposed workflow leverages deep neural network surrogates trained on data obtained from numerical simulations. The use of surrogates allows for a more flexible and faster evaluation of novel designs. The success history-based adaptive differential evolution with linear reduction and the multi-objective evolutionary algorithm based on decomposition were identified as the best-performing algorithms and used to determine the influence of different objectives in the single-objective optimisation and their combined impact on the draft tube design in the multi-objective optimisation. The results for the single-objective algorithm are consistent with those of the multi-objective algorithm when the objectives are considered separately. Multi-objective approach, however, should typically be chosen, especially for computationally inexpensive surrogates. A multi-criteria decision analysis method was used to obtain optimal multi-objective results, showing an improvement of 1.5% and 17% for the pressure recovery factor and drag coefficient, respectively. The difference between the predictions and the numerical results is less than 0.5% for the pressure recovery factor and 3% for the drag coefficient. As the demand for renewable energy continues to increase, the relevance of data-driven optimisation workflows, as discussed in this study, will become increasingly important, especially in the context of global sustainability efforts.

The optimization design of the double-layered material tank is essential to improve the material mixing efficiency and quality in chemical engineering and lithium battery production. The draft tube structure and double-layered impellers affect the flow patterns of the fluid–solid transfer process, and its flow pattern recognition faces significant challenges. This paper presents a fluid–solid mixing transfer modeling method using the CFD-DEM coupling solution method to analyze flow pattern evolution regularities. A porous-based interphase coupling technology solved the interphase force and could be used to acquire accurate particle motion trajectories. The effect mechanism of fluid–solid transfer courses in the double-layered mixing tank with a draft tube can be obtained by analyzing key features, including velocity distribution, circulation flows, power, and particle characteristics. The research results illustrate that the draft tube structure creates two major circulations in the mixing transfer process and changes particle and vortex flow patterns. The circulating motion of the double-layered impellers strengthens the overall fluid circulation, enhances the overall mixing efficiency of the fluid medium, and reduces particle deposition. Numerical results can offer technical guidance for the chemical extraction course and lithium battery slurry mixing. [ABSTRACT FROM AUTHOR]

Francis turbines are adversely affected when operated under part load operating conditions. The increase in pressure pulsations and dynamic stresses results in the less efficient operation of turbine components. Flow instabilities in the draft tube, particularly the rotating vortex rope (RVR), are responsible for such adverse effects. Air injection is a widely used mechanism for attenuating pressure pulsations due to RVR formation and has been employed with varied degrees of success. However, the exact mechanism by which the air influences the turbine flow field is still not fully understood. The influence of peripheral air injection in the draft tube is analysed in the present work using numerical simulations. The effect of injected air on the draft tube flow field at the upper and normal part load is investigated qualitatively and quantitatively. The results elucidate the reasons for air to be beneficial only at low injection rates. The simulations show the manner in which the unsteadiness in the flow increased at high injection rates, leading to additional vortices and secondary flow structures. The results further elucidate the effect of injected air on the changes in the effective area and pressure recovery in the draft tube. [ABSTRACT FROM AUTHOR]

This study aims to provide a comprehensive assessment of single-objective and multi-objective optimisation algorithms for the design of an elbow-type draft tube, as well as to introduce a computationally efficient optimisation workflow. The proposed workflow leverages deep neural network surrogates trained on data obtained from numerical simulations. The use of surrogates allows for a more flexible and faster evaluation of novel designs. The success history-based adaptive differential evolution with linear reduction and the multi-objective evolutionary algorithm based on decomposition were identified as the best-performing algorithms and used to determine the influence of different objectives in the single-objective optimisation and their combined impact on the draft tube design in the multi-objective optimisation. The results for the single-objective algorithm are consistent with those of the multi-objective algorithm when the objectives are considered separately. Multi-objective approach, however, should typically be chosen, especially for computationally inexpensive surrogates. A multi-criteria decision analysis method was used to obtain optimal multi-objective results, showing an improvement of 1.5% and 17% for the pressure recovery factor and drag coefficient, respectively. The difference between the predictions and the numerical results is less than 0.5% for the pressure recovery factor and 3% for the drag coefficient. As the demand for renewable energy continues to increase, the relevance of data-driven optimisation workflows, as discussed in this study, will become increasingly important, especially in the context of global sustainability efforts. • Efficient draft tube design workflow based on DNN surrogates introduced. • Design flexibility ensured through B-spline parameterisation. • MOEA/D and L-SHADE identified as the best-performing algorithms. • A single-objective optimisation approach can be viable depending on the goals. • Multi-objective optimisation provides measurable performance improvements. [ABSTRACT FROM AUTHOR]

Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units. Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines. In this study, ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube. The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation. The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone, which formed a counterclockwise-clockwise-counterclockwise distribution pattern. Simultaneously, there were many secondary flows in the draft tube. Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity. When the cross-sectional shape of the draft tube was changed, the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube, with extreme values at the center and at the walls. The vortex stretching and dilatation terms played a major role in the change in vorticity, with the baroclinic torque having an effect at the center of the vortex rope, this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application [ABSTRACT FROM AUTHOR]

Biomass fast pyrolysis is a promising technology to produce available char and high‐value gas due to its green and sustainable ability. In the current work, the biomass fast pyrolysis in draft tube spouted bed has been numerically investigated via the multiphase particle‐in‐cell model. In this model, gas turbulence is calculated via large eddy simulation and particles are individually tracked in the Lagrangian manner. This model is successfully validated against experimental data. The particle‐scale information of sand and biomass feedstock has been discussed, and the influence of draft tube configuration on the pyrolysis performance has been studied. The results show that the equipment of draft tube prevents gas leakage from spout to annulus, leading to large axial gas flux in the spout. Biomass particles in the spout and freeboard have high temperature and heat‐transfer coefficient. Some biomass particles move along the outer wall of draft tube, indicating that the equipment of draft tube can avoid back‐mixing by preventing direct contact of particles in the spout and annulus. Increasing the height of draft tube results in larger axial gas flux and higher sand heat‐transfer coefficient, while decreases biomass temperature in the spout. The simulation results can offer valuable insights into comprehending intricate reactive gas–solid characteristics and conducting operation and design optimization of spouting apparatus. [ABSTRACT FROM AUTHOR]

Copyright of Large Electric Machine & Hydraulic Turbine is the property of Large Electric Machine & Hydraulic Turbine Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The flow in the draft tube of the water turbine is affected by the upstream flow and the inherent structure accompanied by various undesirable characteristics, affecting the efficient and stable operation of the water turbine. Changing the flow structure downstream of the runner is an important measure to reduce hydraulic loss in the draft tube and improve stability. In this study, three downstream structures of the runner, namely, the non-locking nut, small locking nut, and extended locking nut are numerically calculated and verified using experimental results. The unstable flow characteristics of the draft tube are analyzed using variations in swirling flow, backflow, pressure gradient, and vortex strip. The results show the non-negligible effect of the locking nut, which significantly reduces the rotational momentum flux at the draft tube inlet, accelerates the decay rate of the swirling flow, and suppresses the generation of axial low pressure. The small locking nut significantly reduces the pressure gradient, shortens the backflow zone, and decreases the backflow velocity. The extended locking nut reduces the backflow zone in some sections and reduces the vortex zone of the straight section but prolongs the backflow zone and increases the backflow velocity.

The optimization design of the double-layered material tank is essential to improve the material mixing efficiency and quality in chemical engineering and lithium battery production. The draft tube structure and double-layered impellers affect the flow patterns of the fluid–solid transfer process, and its flow pattern recognition faces significant challenges. This paper presents a fluid–solid mixing transfer modeling method using the CFD-DEM coupling solution method to analyze flow pattern evolution regularities. A porous-based interphase coupling technology solved the interphase force and could be used to acquire accurate particle motion trajectories. The effect mechanism of fluid–solid transfer courses in the double-layered mixing tank with a draft tube can be obtained by analyzing key features, including velocity distribution, circulation flows, power, and particle characteristics. The research results illustrate that the draft tube structure creates two major circulations in the mixing transfer process and changes particle and vortex flow patterns. The circulating motion of the double-layered impellers strengthens the overall fluid circulation, enhances the overall mixing efficiency of the fluid medium, and reduces particle deposition. Numerical results can offer technical guidance for the chemical extraction course and lithium battery slurry mixing.

Hydropower plant vibrations due to pressure fluctuations and their troubleshooting methods are some of the most challenging issues in power plant operation and maintenance. This paper targets these fluctuations in a prototype turbine in two geometries: the initially approved design and the as-built design. Due to topographic conditions downstream, these geometries slightly differ in the draft tube height; the potential effect of such a slight geometrical change on the applicability of troubleshooting techniques is investigated. Therefore, the water flow was simulated using the CFD scheme at three operating points based on the SST k–ω turbulence model, while the injection of water/air was examined to decrease the pressure fluctuations in the draft tube, and the outputs were compared with no-injection simulations. The results show that a slight change in draft tube geometry causes the pressure fluctuations to increase 1.2 to 2.8 times after 4 s injecting at different operating points. The modification in the location of the air injection also could not reduce the increase in pressure fluctuations and caused a 3.6-fold increase in pressure fluctuations. Therefore, the results show that despite water/air injection being a common technique in the hydropower industry to reduce pressure fluctuations, it is effective only in the initially approved design geometry. At the same time, it has a reverse effect on the as-built geometry and increases the pressure fluctuations. This research highlights the importance of binding the construction phase with the design and troubleshooting stages and how slight changes in construction can affect operational issues. [ABSTRACT FROM AUTHOR]

Hydraulic turbines are increasingly used to regulate the electrical grid. They thus have to operate more often at off-design conditions where instabilities may develop leading to large pressure pulsations decreasing the life of the machines. In the present study, an adjustable guide vane system in the draft tube of a single regulated hydraulic turbine is developed. The aim is to mitigate the pressure pulsations when the turbine operates at part load operational regimes without significantly compromising the hydraulic efficiency of the turbine. The draft tube guide vane system, named DTGV, is composed of three guide vanes. Each guide vanes comprise two individual hydrofoils. The upper hydrofoil can rotate around an axis up to ±45°, and the lower is fixed. Therefore, the guide vanes are adjustable. The rotating vortex rope mitigation was investigated at two part-load operational regimes at a 12 m turbine head, a) Q/Q BEP = 0.59, and b) Q/Q BEP = 0.71. The results indicate that the DTGV system significantly mitigates the pressure pulsations, thereby improving the flexible operation of the turbine. The best mitigation outcome was for 0 GV configuration at both part-load operating conditions. The mitigation effects are better when the operating condition approaches BEP, and the rotating mode of the pressure pulsations tends to go towards the runner frequency (f/f 0 = 1). The hydraulic efficiency is found to be marginally affected by the guide vane system at part load operations and is improved at the best efficiency point (Q/Q BEP = 1) and high load Q/Q BEP = 1.21. [ABSTRACT FROM AUTHOR]

Pumped storage hydropower plants are renewable energy systems that are effective in saving energy and solving electricity peak-on shortage. Seawater pumped storage hydropower plants are a novel type of pumped storage hydropower plant specifically supplying electric power for ocean islands with the support of solar energy and wind energy. Compared with traditional pumped storage hydropower plants that are constructed on the mainland, seawater pumped storage hydropower plants should take the influence of the complex marine environment, such as extreme waves and winds, into consideration. Taking the characteristics of waves near islands in the East China Sea as an example, we explored the transient hydraulic characteristics in the draft tube of a pump turbine under wave disturbance using a sliding grid interface and the detached eddy simulation (DES) turbulence model. By analyzing the characteristics of unsteady flow in the draft tube, the vortex characteristics under the Q criterion, the frequency characteristics of the pressure pulsation, the evolution law of the internal fluid, and the propagation law of the pressure pulsation were explored. For the situation without wave disturbance, an obvious eccentric vortex in the straight cone section of the draft tube was observed in the case where the opening of the guide vane was small. With the increase in the opening of the guide vane, the eccentric vortex gradually dissipated. For the situation with wave disturbance, the main frequency of the draft tube equaled the frequency of the wave disturbance, the maximum pressure pulsation at the selected monitoring points increased 5 to 15 times, and the superposition of the wave pressure pulsation signals and the draft tube pressure pulsation produced more low-frequency, high-amplitude pressure pulsation signals. Even though the pressure pulsation frequency spectrum varied a lot, the frequency domain of the pressure pulsation without wave disturbance still existed. In addition, the wave disturbance merely varied with the pressure of the draft tube. The influence of wave disturbance on the pressure distribution in the draft tube was relatively small. The results can provide a reference for the operation of seawater pumped storage hydropower plants. [ABSTRACT FROM AUTHOR]

Copyright of Pearl River is the property of Pearl River Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper describes an approach to modeling the flow velocity distribution at the inlet of the hydro turbine draft tube that can significantly reduce test costs. The flow is modeled using a special swirler consisting of a combination of two blade rows: fixed and rotating. The previously proposed method for designing swirlers to generate velocity fields corresponding to the velocity distributions behind real hydro turbines was used to design eight blade rows modeling the velocity distributions in optimal operating modes of hydro turbines of various types. This paper presents a test numerical calculation of the flow parameters using Ansys code and a comparison of design velocity distributions with experimental velocity profiles obtained on an aerodynamic rig using a laser Doppler anemometer. The design, calculated, and experimental flow velocity profiles at the draft tube inlet are shown to be in satisfactory agreement. Thus, the promising approach to the experimental modeling of hydro turbine flow was successfully tested. [ABSTRACT FROM AUTHOR]

We study the flow in a model Francis-99 draft tube for partial load conditions using Large-eddy simulation. The swirl is produced by the runner rotating with a constant angular velocity. Within the validation step, we compare results of eddy-resolving simulations with our Particle image velocimetry (PIV) and pressure measurements for three flow cases with different incoming flow rates. The time-averaged velocity fields agree well in experiments and simulation. To study the dynamical features, we analyze spectral characteristics of the flow featuring a strong coherent component. This vortical structure corresponds to the precessing vortex core (PVC) changing the shape and amplitude with the increase in the bulk velocity. [ABSTRACT FROM AUTHOR]

In the hydropower sector, the weight of electro-mechanical equipment is an important input data. During the design stage, it allows to estimate material cost, to perform Life Cycle Assessments and to consider adequate load factors on the supporting structures. At the end of the lifetime, in case of dismantling or retrofitting, the estimation of the equipment weight allows to appraise the material value and to plan the operational activities. However, the engineering knowledge is quite fragmented and limited on this topic, and only a few weight equations are available in the literature. In this contribution, the available equations are firstly reviewed and discussed. Secondly, data were collected both from the literature and from hydropower companies, and generalized to provide expeditious equations. The equations presented in this paper allow for a preliminary estimate of the weight of: 1) the runner of Pelton, Kaplan, Bulb, Cross-Flow (Banki type) and Francis turbines, and water wheels; 2) the casing of Pelton and reaction turbines; 3) draft tubes; 4) electric generators. Data on Vortex, Turgo and Hydrokinetic turbines, Archimedes screws and guide vanes are presented. The opportunities associated to innovative and lighter construction materials are discussed.

The draft tube elbow was modelled using the fundamental geometry of GAMM Francis turbine. Its purpose was to design a draft tube with improved hydrodynamic performance This was accomplished by integrating unfasten resource and commercialized technologies to optimize and update the shape and CFD grid, and analyzing pressure retrieval and mechanical power wounded next to draft tube intend through Computational Fluid Dynamics (CFD). A technique was used to evaluate the functioning of an elbow draft tube. According to CFD, an 18.8° inclined angle has been the best way in blocking the production of physically powerful swirl stream and resulting in reducing the amplitude of pressure fluctuation. The blade passing frequency dominates the draft tube entrance, influencing local pressure recovery; however, the low-frequency core instability quickly diffuses and taps it.

As a limiting factor in power generation, especially in part-loads, turbulence is considered an important phenomenon in hydropower plants. In this study, the pressure pulsation measurements are done for Darian Hydropower Plant in Iran, which is composed of three 70 MW units with a common penstock. The frequency spectrum for different features such as rotor-stator interactions, draft tube vortex rope, and surge tank fluctuations is obtained and discussed in detail. Pressure pulsation measurements were obtained while one of the units (i.e., Unit I) was in operation, and the other units (Units II, III) were out of operation. In addition to the in-operation units, the effect of pressure pulsation on the out of operation units is also studied comprehensively. The results show that to avoid the destructive effect of pressure pulsation, the output power of the in-operation unit should not be lower than 55 MW (i.e., a part load lower than 78 % of the full load). Results demonstrate that at lower power levels pressure pulsation is significant likely because the flow characteristics are rather significantly different than the conditions considered for the design of the plant. Moreover, it is found that most of the pressure waves generated by the turbulent flow of the in-operation unit waterway have considerable impacts on the neighboring units. A very good agreement between the expected theoretical frequencies and measured frequencies are observed for various pressure pulsation phenomena, as well.

The installation of new and revitalization of existing hydropower requires the optimal design of hydraulic turbine parts, which were previously mostly based on simplified analytical methods and engineering practices. With the increase in computational power, optimization methods now present an effective approach to the improvement of the geometry of turbine parts, thus enabling fine geometry-tuning adjustments of site specifics. However, despite continually increasing computational power, such numerical optimizations still require substantial resources and time. Therefore, in the proposed paper, extensive analysis of different numerical simplifications was conducted to determine the best trade-off between accuracy and the required computational resources for draft tube optimization. Additionally, the influence of geometry parametrization in terms of greater geometry flexibility, different goal functions, and optimization parameters was investigated. Within the considered constraints, a novel draft tube geometry was obtained, with the elbow displacements toward the draft tube exit, a shape that could not be obtained with the usual draft tube parametrization. It was also observed that geometry improvements for a single operating point did not provide improvements for other operating points. The obtained findings regarding the numerical and optimization setup can be used as guidelines for future optimization research, where multiobjective optimization for multiple operating points should be further investigated. [ABSTRACT FROM AUTHOR]

Vortex rope is a common phenomenon in the draft tube of hydraulic turbines. It may cause strong pressure pulsation, noise, and strong vibration of the unit especially when it is helical. Therefore, the study of vortex rope is of great significance. In order to study the helical vortex rope, the embedded large eddy simulation (ELES) method in the hybrid methods is used based on the vortex rope generator case. The Liutex method can show the three-dimensional shape of the vortex rope well. In order to quantitatively describe the helical vortex rope, the three-dimensional structure is divided into multiple two-dimensional sections, and then the shape of vortex rope on each section is processed to extract the perimeter and area of the vortex. Combined with the change trend of vortex number and section area, the helical vortex rope is divided into four zones. Then, the fractal dimension on each zone and section can be obtained, and it can be used to quantitatively analyze the change trend of the vortex rope in time and space. The fractal analysis method can be applied to the analysis of the vortex rope in the draft tube to help judge the flow pattern shape and the stability of the unit operating conditions. [ABSTRACT FROM AUTHOR]

Hydropower plant vibrations due to pressure fluctuations and their troubleshooting methods are some of the most challenging issues in power plant operation and maintenance. This paper targets these fluctuations in a prototype turbine in two geometries: the initially approved design and the as-built design. Due to topographic conditions downstream, these geometries slightly differ in the draft tube height; the potential effect of such a slight geometrical change on the applicability of troubleshooting techniques is investigated. Therefore, the water flow was simulated using the CFD scheme at three operating points based on the SST k–ω turbulence model, while the injection of water/air was examined to decrease the pressure fluctuations in the draft tube, and the outputs were compared with no-injection simulations. The results show that a slight change in draft tube geometry causes the pressure fluctuations to increase 1.2 to 2.8 times after 4 s injecting at different operating points. The modification in the location of the air injection also could not reduce the increase in pressure fluctuations and caused a 3.6-fold increase in pressure fluctuations. Therefore, the results show that despite water/air injection being a common technique in the hydropower industry to reduce pressure fluctuations, it is effective only in the initially approved design geometry. At the same time, it has a reverse effect on the as-built geometry and increases the pressure fluctuations. This research highlights the importance of binding the construction phase with the design and troubleshooting stages and how slight changes in construction can affect operational issues.

• Heat transfer performance of a Lightnin stirred reactor coupled with draft tube has been investigated. • The optimized impeller off-bottom clearance has been obtained in the draft tube stirred tank. • The time-correlation variation of heating rate and synergistic angle has been investigated. • A correlation formula coupled by multifactor for enhancing heat transfer in a stirred tank has been proposed. The heat transfer issue in stirred tanks is a prevalent concern in the industry. This article aims to investigate the fluid flow and heat transfer within a stirred tank equipped with a Lightnin A320 impeller coupled with a draft tube (DT) structure. The heat transfer performance of a 37 L jacket stirred tank is experimentally measured with the rotation speeds of 50 ‒ 300 RPM. The effects of off-bottom clearances and rotational speeds on mixing and heat transfer performance are explored using Computational Fluid Dynamics (CFD) by flow patterns, local velocity, turbulent kinetic energy (TKE), helicity, vorticity, heat transfer coefficient, synergy angle, extensional efficiency, and coefficient of variation (CoV) , respectively. The numerically predicted temperature curves have a good agreement with the experimental results. An optimal off-bottom clearance with C/D = 0.43 is found in this stirred tank. Furthermore, empirical correlations are developed to predict heat transfer performance by analyzing the relationship between wall heat transfer coefficient, power consumption, and heat transfer rate. By evaluating the variation of the temperature gradient synergy angle with time and rotational speed of the stirred tank, it was determined that a stabilization time of 120 s is required for the synergy angle. In the area outside the DT, 80 % of the region exhibits extensional efficiency values greater than 0.5. For 100 ‒ 300 RPM, achieving a CoV of 0.01 requires 48.36 %, 67.26 %, 76.81 %, 82.34 %, and 85.67 % less time compared to that of 50 RPM, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

Copyright of Energy Chemical Industry is the property of Energy Chemical Industry Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The flow characteristics of the draft tube of a Francis turbine have a significant influence on turbine stability. Numerical simulations were performed for a Francis turbine under three different output conditions of 20%, 100%, and 120% at the rated and maximum heads. Laser Doppler velocimetry (LDV) tests were conducted to test the flow characteristics of the draft tube of the Francis turbine model. The flow characteristics in the draft tube, the mechanism of the flow characteristics change, and the effect of the opening on the vortex rope were analyzed. The results showed that the large and invisible vortex in the conical cross-section at the inlet of the draft tube gradually changed to a tangible vortex rope as the guide vane opening (GVO) increased. The pressure and velocity are significantly influenced by the GVO, and the flow characteristics in the draft tube improve as the GVO increases. Simultaneously, the influence range of the vortex rope increased as the head increased. [ABSTRACT FROM AUTHOR]

The draft tube is one of the main components that integrate a turbine, since it has the function of recovering the residual kinetic energy after the runner by the pressure energy. The search for a draft tube design that increases the efficiency of the turbine is always an engineering challenge. The hydromechanics components geometry optimization can be accomplished through the integration of optimization methods and CFD tools. In this work, the geometric optimization of a double diffuser draft tube of a Bulb turbine applied to ultra-low heads is presented, with the objectives of maximizing the pressure recovery coefficient, Cp, and increasing the hydraulic efficiency of the turbine, ηh. These improvements would make it possible to reduce the longitudinal length of the draft tube, thereby, making an easier insertion of this kind of turbines in water transport systems, with pressures around 3 [mH2O]. The optimization methodology was performed in the meridional plane, using twelve geometric variables in the draft tube through the integration of optimization methods and computational fluid dynamics. The optimized geometry obtained showed an increase in the Cp value of 0.71516, from the original geometry, to 0.83080. The results were extended to the 3D flow analysis, where the optimized turbine showed efficiency gains of 82% to 84%, when compared to the original turbine considering that its total length was reduced and its geometry simplified, resulting in a more compact and versatile equipment. The study also concluded that the applied methodology can be extended to other similar optimization problems in the design of hydraulic machines‎.

A technique is proposed for generating the set of surfaces of a toroidal draft tube of a hydraulic turbine depending on 19 geometric parameters and for constructing grids in the area of the tube to search for the optimal shape based on numerical simulation of flows. [ABSTRACT FROM AUTHOR]

Mortality of fish entering the turbine draft tube (DT) from the tailrace is common during turbine startup or dewatering in Brazilian hydropower dams. Mortality can be reduced if such operations occur when few fish are present in the DT, but estimating abundance therein using traditional gears (e.g., cast net, gillnet, hook-and-line) is constrained by flow and access. We deployed a Dual frequency IDentification SONar (DIDSON) to record and count fish in the DT for the first time using an innovative approach. Methods used elsewhere for manual counting fish in DIDSON images generated dissimilar results. Therefore, we compared three methods of counting fish manually in the frames of DIDSON software from two Brazilian dams: numerical counting (number of fish in the frame), qualitative counting (percent of the frame occupied by fish), and intersection counting (number of intersections of the grid frame with fish). We assumed that the numerical counting provided the best estimates of the true value but could not be used in 32.2% of the frames from one of the dams due to the presence of uncountable aggregation of fish, bubble curtain, or poor contrast between fish and the DT floor. Qualitative counting was the most congruent, whereas intersection counting was the least, based on comparisons with numerical counting. [ABSTRACT FROM AUTHOR]

The draft tube is one of the main components that integrate a turbine, since it has the function of recovering the residual kinetic energy after the runner by the pressure energy. The search for a draft tube design that increases the efficiency of the turbine is always an engineering challenge. The hydromechanics components geometry optimization can be accomplished through the integration of optimization methods and CFD tools. In this work, the geometric optimization of a double diffuser draft tube of a Bulb turbine applied to ultra-low heads is presented, with the objectives of maximizing the pressure recovery coefficient, Cp, and increasing the hydraulic efficiency of the turbine, ηh. These improvements would make it possible to reduce the longitudinal length of the draft tube, thereby, making an easier insertion of this kind of turbines in water transport systems, with pressures around 3 [mH2O]. The optimization methodology was performed in the meridional plane, using twelve geometric variables in the draft tube through the integration of optimization methods and computational fluid dynamics. The optimized geometry obtained showed an increase in the Cp value of 0.71516, from the original geometry, to 0.83080. The results were extended to the 3D flow analysis, where the optimized turbine showed efficiency gains of 82% to 84%, when compared to the original turbine considering that its total length was reduced and its geometry simplified, resulting in a more compact and versatile equipment. The study also concluded that the applied methodology can be extended to other similar optimization problems in the design of hydraulic machines. [ABSTRACT FROM AUTHOR]

The installation of new and revitalization of existing hydropower requires the optimal design of hydraulic turbine parts, which were previously mostly based on simplified analytical methods and engineering practices. With the increase in computational power, optimization methods now present an effective approach to the improvement of the geometry of turbine parts, thus enabling fine geometry-tuning adjustments of site specifics. However, despite continually increasing computational power, such numerical optimizations still require substantial resources and time. Therefore, in the proposed paper, extensive analysis of different numerical simplifications was conducted to determine the best trade-off between accuracy and the required computational resources for draft tube optimization. Additionally, the influence of geometry parametrization in terms of greater geometry flexibility, different goal functions, and optimization parameters was investigated. Within the considered constraints, a novel draft tube geometry was obtained, with the elbow displacements toward the draft tube exit, a shape that could not be obtained with the usual draft tube parametrization. It was also observed that geometry improvements for a single operating point did not provide improvements for other operating points. The obtained findings regarding the numerical and optimization setup can be used as guidelines for future optimization research, where multiobjective optimization for multiple operating points should be further investigated.

Spouted beds are extensively used in different industries. The minimum spouting velocity is a critical hydrodynamic parameter needed for the design and scale-up of these systems. This study deals with an ensemble method involving Multi-Layer Perceptron (MLP) network, the Adaptive Neuro-fuzzy Inference System (ANFIS), the Gaussian Process Regression (GPR), and a Regression Tree (RT) model for predicting minimum spouting velocity for coarse particles in conical spouted beds equipped with nonporous draft tubes (CSBDTs) and conical-cylindrical spouted beds. Some dimensionless variables related to the physical properties of the conical bed and particles' material were constructed and used as model inputs. The proposed method was validated against the measured data. The results revealed that the ensemble method was capable of predicting the minimum spouting velocity with an average absolute relative error (AARE) of 10.52% and 10.35% for the testing data points in the case of CSBDTs and conventional spouted beds, respectively. It was also shown that the proposed ensemble method provided the best results in comparison with the other methods. Therefore, the ensemble method is a useful and powerful technique for predicting the minimum spouting velocity in spouted beds with and without the draft tube. [ABSTRACT FROM AUTHOR]

Drying is a highly energy-intensive process and dryers are considered one of the most energy-consuming industrial equipment. Nevertheless, the energy contribution of the draft tube in the spouted bed has hardly been studied. This equipment is widely recognized as a versatile and efficient gas-solid contact method for several chemical and physical operations. Thus, the objective of this study is to perform an energy analysis of a draft tube conical spouted bed for particulate materials. Drying of alumina, soybean, and barley has been performed with three different configurations: without tube and with nonporous and open-sided tubes. Energy Efficiency, Drying Efficiency, and Specific Energy Consumption have been the parameters considered for energy analysis. The nonporous tube provided the best energy performance for diffusive materials, such as barley and soybean particles, with reductions in the energy consumption in the range from 31.60% to 42.40% in relation to configuration without tube. The configurations with open-sided tube and without tube provided similar energy performance for all materials. Therefore, this study contributes to support that draft tubes are promising devices for improving energy issues in the spouted bed, mainly in the processing of low moisture materials. [Display omitted] • The open-sided draft tube provides the best energy utilization for materials with negligible internal mass transfer resistance. • The nonporous tube provides the best energy performance for porous materials with internal mass transfer resistance. • Draft tubes are promising devices for improving energy issues in spouted beds. [ABSTRACT FROM AUTHOR]

When the pump-turbine operates at off-design conditions, vortex rope usually occurs in the draft tube and causes low-frequency pressure fluctuations. In this paper, the evolution of the vortex rope and its association with the low-frequency pressure fluctuations under typical operating conditions are investigated. The results indicate that: 1) The frequency of pressure fluctuation is mainly affected by the vortex's rotation frequency in the draft tube without cavitation. While when cavitation occurs, the frequency of pressure fluctuations in the draft tube is primarily affected by the cavitation volume evolution; 2) Under the non-cavitation condition, the overall vortex rope behaves as a spiral vortex rope under part-load condition, a slender column under design condition, and pear-shaped vortex rope under full-load condition. The vortex rope directly disappears when cavitation occurs under part-load condition. In contrast, the vortex rope becomes unstable, and changes from a single-phase vortex rope to a multi-phase vortex rope under the design condition. While at the full-load condition, the vortex rope becomes slenderer, and the rotation is more noticeable than under the non-cavitation condition. • A new multiphase flow simulation method is proposed and proved in pump-turbine. • The correlation mechanism between vortex and pressure fluctuations is revealed. • The spatial distribution law of low-frequency pressure fluctuations is studied. [ABSTRACT FROM AUTHOR]

During biomass pyrolysis within spouted reactor, particles exhibit behavior characterized by polydispersity. To explore the impact of polydispersity of bed materials on the biomass pyrolysis, the multiphase particle-in-cell model is constructed to simulate such process. The focus of the study is examining the impact of size distribution of solid materials and the presence of a draft tube on the particle-level properties. The results show that the yields of Gas1 and tar during the first pyrolysis increase about 13.1 % and 14.8 %, respectively, as the PSD width of sand increase from 0.1 to 0.7. In addition, the influence of the draft tube is primarily centered on enhancing interphase interactions rather than pyrolysis yields when a fountain confiner is applied. Fine particles mainly distribute along the interphase of annulus and its vicinity while coarse particles mainly accumulate along the interphase of annulus and spout. Expanding the PSD widths of bed materials from 0.1 to 0.7 results in an approximate temperature increase of 10 K in the floating biomass. The variation of particle slip velocity and heat transfer coefficient exhibits similar trend, mainly due to their interrelation in convective heat transfer. These findings hold valuable insights that can guide optimization design and parameter selection in the conical fountain confined spouted bed reactors. [ABSTRACT FROM AUTHOR]

Vortex rope is a common phenomenon in the draft tube of hydraulic turbines. It may cause strong pressure pulsation, noise, and strong vibration of the unit especially when it is helical. Therefore, the study of vortex rope is of great significance. In order to study the helical vortex rope, the embedded large eddy simulation (ELES) method in the hybrid methods is used based on the vortex rope generator case. The Liutex method can show the three-dimensional shape of the vortex rope well. In order to quantitatively describe the helical vortex rope, the three-dimensional structure is divided into multiple two-dimensional sections, and then the shape of vortex rope on each section is processed to extract the perimeter and area of the vortex. Combined with the change trend of vortex number and section area, the helical vortex rope is divided into four zones. Then, the fractal dimension on each zone and section can be obtained, and it can be used to quantitatively analyze the change trend of the vortex rope in time and space. The fractal analysis method can be applied to the analysis of the vortex rope in the draft tube to help judge the flow pattern shape and the stability of the unit operating conditions.

The flow characteristics of the draft tube of a Francis turbine have a significant influence on turbine stability. Numerical simulations were performed for a Francis turbine under three different output conditions of 20%, 100%, and 120% at the rated and maximum heads. Laser Doppler velocimetry (LDV) tests were conducted to test the flow characteristics of the draft tube of the Francis turbine model. The flow characteristics in the draft tube, the mechanism of the flow characteristics change, and the effect of the opening on the vortex rope were analyzed. The results showed that the large and invisible vortex in the conical cross-section at the inlet of the draft tube gradually changed to a tangible vortex rope as the guide vane opening (GVO) increased. The pressure and velocity are significantly influenced by the GVO, and the flow characteristics in the draft tube improve as the GVO increases. Simultaneously, the influence range of the vortex rope increased as the head increased.