Draft Tube

The turbine is a heart of power generation in a hydro-electric power system. A variety of different turbines are available for that purpose. The common types of Hydraulic turbines are; Pelton, cross flow, Francis, Kaplan, and propeller turbine. However, using conventional turbines for low head and flow rate (i.e. micro hydropower) applications are not economically feasible. A low-cost alternative is to use the pump as a turbine. In this paper, existing Peer-reviewed articles from (Scopus, google scholar, umbrella, etc.) that are directly related to pump running as a turbine are collected and reviewed. Theoretical, numerical, and experimental investigations are considered. Performance improvement techniques for PAT are summarized and research gaps in related works are identified.

The use of bioenergy has increased globally in recent years, as has the utilization of biomaterials for various new product solutions through various biorefinery concepts. In this study, we introduce the concept of using a mechanical dewatering press in combination with thermal drying in a pellet plant. The purpose of the study is to increase the understanding of the effects a mechanical dewatering press has in a pellet production chain and investigate whether a pellet plant could thus become a biorefinery. The evaluations in this study are based on industrial data and initial tests at the university. The results show that the concept of using the mechanical dewatering press together with a packed moving bed dryer reduces energy use by 50%, compared to using only a packed moving bed dryer. The press water could be used as a raw material for biogas, bioplastics, and biohydrogen. Hence, this study points out the possibilities of a pellet plant increasing the efficiency of the drying s...

Micro hydropower station is one of the clean choices for offgrid points with available hydropotential. The challenging in this type of energy production is the high capital cost of the installed capacity that is worse for low-head micro hydropower stations. Turbine price is the main problem for this type of energy production. In this research, a simple machine has been introduced instead of conventional propeller turbines. The key is using an axial pump as a propeller turbine. In the present research, a propeller pump was simulated as a turbine by numerical methods. Computational fluid dynamics (CFD) was adopted in the direct and reverse modes performance prediction of a single propeller pump. To give a more accurate CFD result, all domains within the machine control volume were modeled and hexahedral structured mesh was generated during CFD simulation. Complete performance curves of its pump and turbine modes were acquired. For verification of the numerical results, the machine has...

Oxygenation is an important parameter involved in the design and operation of mixing-sparging bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (k L a). The operational conditions of a stirred, submerged aerated 2-L bioreactor have been optimized by studying the influence of a second liquid phase with higher oxygen affinity (perfluorodecalin or olive oil) in the k L a. Using k L a measurements, the influence of the following parameters on the oxygen transfer rate was evaluated: the volume of working medium, the type of impellers and their position, the organic phase concentration, the aqueous phase composition, and the concentration of inactive biomass. This study shows that the best experimental conditions were achieved with a perfluorodecalin volume fraction of 0.20, mixing using two Rushton turbines with six vertical blades and in the presence of YPD medium as the aqueous phase, with a k L a value of 64.6 h À1 . The addition of 20% of perfluorodecalin in these conditions provided a k L a enhancement of 25% when pure water was the aqueous phase and a 230% enhancement when YPD medium was used in comparison to their respective controls (no perfluorodecalin). Furthermore it is shown that the presence of olive oil as a second liquid phase is not beneficial to the oxygen transfer rate enhancement, leading to a decrease in the k L a values for all the concentrations studied. It was also observed that the magnitude of the enhancement of the k L a values by perfluorodecalin depends on the biomass concentration present.

Microalgae are fast growing photoynthetic microorganisms and it have very wide range of industrial applications such as biofuels and wastewater treatment. These cells can be grown in a wide variety of systems ranging from open culture systems (e.g., ponds) to closed culture systems of photobioreactor (e.g., airlift). The open culture systems exist in the external environment, and hence, are not intrinsically controllable. However, the microalgae production in enclosed photobioreactors faces prohibitively high production costs with special difficulty in reactor design and scale-up. The light availability and utilization efficiency in the photobioreactor in terms of design and scale-up consider as the major problem in this system. It has been found that hydrodynamics and mixing can significantly improve the biomass yield by enhanced the light use efficiency. However, the hydrodynamics analysis, and their interacts with photosynthesis in real culturing system is remain unclear. The overall objective of this study is to advance the understanding of hydrodynamics' role in the photosynthesis and thus the photobioreactor performance. The local flow dynamics in a split internal-loop photobioreactor were study by applied a sophisticated Radioactive Particle Tracking (RPT) and advanced Computer Tomography (CT) techniques. Based on the findings, fundamentally based dynamic modeling approach is developed for photobioreactor performance evaluation, which integrates the knowledge of photosynthesis, hydrodynamics, and irradiance. Finally, Scenedesmus sp. was grown in split column. The biomass concentrations, flow dynamics, physical properties, and irradiance distribution of the culturing systems were monitored. Good agreements between the predictions by the developed dynamic model and the experimental data were achieved, indicating the applicability of the dynamic model in industrial interested condition. v ACKNOWLEDGMENTS After a journey of research effort and diligence culminated in the completion of this work, my praises and thanks are to Allah Almighty for his grace and blessing to me. I wish to express my sincerest thanks and gratitude to my advisor Prof. Muthanna Al-Dahhan for his considerable efforts, advice, guidance, encouragement, and support throughout my Ph.D. study, which helped me to overcome many obstacles, and his critical review of my papers significantly enhanced my skills. I am also extending my sincere thanks to all members of my committee, Dr. Joseph Smith, Dr. Daniel Forciniti, Dr. Fatih Dogan, Dr. Shoaib Usman, and Dr. Joontaek Park, for examining my dissertation and enriching it with valuable tips and guidance that help to make it the best. I want to express my gratitude to my sponsor, Ministry of Higher Education in Iraq, for awarding me a fully funded scholarship and for their friendly assistance throughout my Ph.D. study. I would like to gratefully thank my lab-mate, and my lifetime friend, Abbas Sultan, for his valuable assistance and insightful discussions and suggestions. I appreciatively would like to thank my research group members. My special thanks and appreciation also goes to Dr.

In this work, the effect of inlet-gas superficial velocity over the circulation liquid velocity, gas holdup and mass transfer, from an airlift bioreactor with settler were studied by Computational Fluid Dynamics (CFD) modeling and contrasted with experimental results. Multiphase mixture model and κ-ε turbulence model were used to describe the two phases gas-liquid flow pattern in airlift bioreactor. The hydrodynamic parameters such as liquid circulation velocity and gas holdup were computed by solving the governing equations of continuity, moment and turbulence transport using the finite volume method. Global mass transfer coefficient was evaluated through the Higbie’s penetration theory and the two-phase fluid dynamic theory. Comparison between our numerical data and experimental data previously reported in the literature was done. Numerical and experimental data were very close, and the differences found were discussed in terms of the limitations of this study.

This paper provides an overview of the ancient evolution, design and development of different types of spiral tube water wheel pumping system (STWWPS). It has always been a challenge to lift water and carry it to some other location for executing meaningful work, making use of the alternative sources of power. Several kinds of non-conventional energy sources and techniques have been tried. Each one is having its own merits and demerits. Making use of the kinetic energy of lowing water can be achieved through different kinds of water wheel. Spiral tube powered by kinetic energy of lowing water has been utilized for lifting and carrying water for irrigation and other purposes, contributing to the replacement of conventional diesel and electric power sources. These conventional sources are expensive (Diesel) and often unreliable in rural areas (Electricity). This review paper examines the design, development, and performance evaluation of various spiral tube pumping systems, including single, double, multilayer, pedal type, four scoop type, and multi-purpose models. It examines the load torque, power, ef iciency, and stress analysis of shaft and bearing, and the impact of rotational speed, submerged ratio, and number of spiral pipes on the performance of the pumping system. The working principle allows these pumps to create a column of water within its coil that alternatively the air which is compressed as it moves towards the center of wheel. These pumps not only save electricity and diesel cost but the maintenance cost is also low apart from contributing to the clean environment.

In the study, tip-clearance cavitation inception and development was studied in the gap between an end face of a NACA0022-34 hydrofoil and a transparent sidewall of a test channel. The experiments were carried out for the attack angles of 3º and 9º and the gap width of 0.4 to 0.8 mm under various flow conditions on the cavitation number. In order to observe the tip-clearance cavitation inception and its dynamics, a high-speed visualization was applied. The leakage flow velocity was measured inside the clearance by a modified PTV technique. It was shown that unsteady dynamics of the primary cavity on the foil suction side affects the leakage flow direction and the gap cavitation evolution. An increase of the gap width causes the gap cavitation to be initiated at higher cavitation numbers.

This paper presents the results of simulations of the complete three-dimensional fluid flow through the Spiral Casing, Stay Vane, Guide Vane, and then through the Francis turbine runner of the Derbendikan power station. To investigate the flow in the Francis turbine and also to identify the loads acting on the turbine blades, a three-dimensional model was prepared according to specifications provided. The results show that the maximum absolute pressure of 4.4x10 5 Pa is reached at the leading edge of the turbine runner and the maximum tangential velocity reaches 33 m/s in the turbine runner.

Detailed knowledge of particle motion is essential in better understanding fluidised bed coating processes. This paper reports on the use of Positron Emission Particle Tracking (PEPT) in order to visualise and quantify the features of the powder movement inside a laboratory-scale GPCG-1 fluidised bed coater (Glatt GmbH, Germany) with a tapered (conical) chamber. In all cases, a clear circulating motion, upwards in the centre and downwards along the walls, was revealed. This circulating pattern lends itself to operations such as particle coating, where controlled application of the coating onto the particles is essential. In contrast to the fluidisation patterns observed in cylindrical fluidised beds or spouted beds without a draft tube, radial movement was stronger and occurred at all heights in the powder bed. By introducing a binary nozzle and increasing the nozzle atomisation air pressure, the circulating motion of the fluidised particles in a tapered vessel was found to be accelerated. When spraying a coating solution downwards onto the fluidised powder particles, effects on the particle motion, depending on coating solution properties and process parameters, were observed. Besides visualisation, PEPT was also used to derive quantitative information such as bed height and particle circulation time, as well as to investigate the size of the coating zone. Generally, it was demonstrated that PEPT can be successfully used to characterise the particle motion in a tapered fluidised bed under both drying and coating conditions.

The 1000 MW Francis turbine unit at the Baihetan hydropower station is the maximum capacity unit in the world at present, and it has adopted the runner type with long and short blades. For this ultra-high output Francis turbine, especially with the breakthrough runner structure, the hydraulic excitation phenomenon caused by internal dynamic and static interference is the key factor for the stability of the unit. In this study, the 1000 MW Francis turbine unit is taken as the research object, and the rated output conditions with different guide vane openings are selected for comparative analysis. The flow field structure and the pressure pulsation characteristics inside the guide vane and runner under different openings are obtained. The distribution characteristics and evolution law of the vortex in the runner under different guide vane openings are analyzed. The results show that the dynamic and static interference between the runner and the guide vane induces the local high-speed ...

A forced circulation pumped loop reactor is characterized for oxygen transfer in air-water system. Overall mass transfer coefficient (k L a) data are reported for airlift and forced circulation modes of operation, for liquid circulation rates of up to 2 m 3 /h. Highest values of oxygen transfer efficiency were attained at specific power input values of ≤100 W/m 3 when the forced circulation rates were ≤0.5 m 3 /h. Higher values of forced circulation rate reduced mass transfer efficiency, but reactor was always more efficient than a propeller loop reactor. The k L a values obtained at high rates of pumped liquid circulation were substantially greater than could be attained in the airlift mode of operation. Forced circulation produced more uniform and small bubbles, compared to operation as an airlift reactor. At high rates of forced circulation (e.g. 2 m 3 /h), presence of relatively light (density = 931.8 kg/m 3 ) suspended hydrophobic polypropylene particles (average diameter = 4.7 mm) at concentrations of 1.6 and 3.2% (v/v), barely affected k L a compared to solids-free operation. The reactor used had an aspect ratio of 6.2 and downcomer-to-riser cross-sectional area ratio of 0.032. The forced flow was injected in the annular riser zone.

Gas holdup and mixing time were characterized in a forced circulation internal loop draft-tube reactor (unaerated aspect ratio ≈ 6, downcomerto-riser cross-sectional area ratio = 0.493) as functions of the forced liquid superficial velocity in the riser (U Lr ) and the gas superficial velocity in the riser (U Gr ). Data were obtained in air-water system. The operation ranges were 0 ≤ U Lr ≤ 0.051 m/s and 7.8 × 10 -3 ≤ U Gr ≤ 3.9 × 10 -2 m/s for the liquid and gas velocities, respectively. Under forced flow conditions the reactor always operated in the bubble flow regimen, but operation as an airlift reactor (i.e. no forced flow of liquid) produced a heterogeneous churn-turbulent flow regimen. Forced flow of liquid enhanced gas holdup in comparison with the airlift mode of operation. Mixing time generally declined with increased flow rates of gas and liquid. The ability to maintain a bubble flow regimen through forced flow of liquid allowed the reactor to attain gas holdup values of >0.12 that are difficult to achieve in air-water in conventional bubble columns and airlift reactors.

This work investigates the unsteady pressure fluctuations in a hydraulic turbine that are observed during steep ramping. Although hydraulic turbines are expected to operate seamlessly during steep ramping, the resulting pressure amplitudes are so significant that they take a toll on a machine's operating life. Objective of the present study is to investigate time-dependent pressure amplitudes in the vaneless space, runner and draft tube during power ramping-up and -down under variable-speed configuration. Novelty is to vary both discharge and rotational speed of a runner. The measurements are performed on a high-head model Francis turbine. The investigations revealed that amplitudes of characteristics frequencies, especially rotor-stator interaction, are small during steep ramping however, at the end of transient cycle, the amplitudes quickly increased 30-fold. During steep ramping, blade passing frequency was appeared in the runner, which is uncommon phenomenon in high-head Francis turbines. Strong reflection of pressure waves towards runner from vaneless space (guide vane walls) may be one of the causes for the appearance of blade passing frequency in the runner.

Dam and powerhouse operation sustainability is a major concern from the hydraulic engineering perspective. Powerhouse operation is one of the main sources of vibrations in the dam structure and hydropower plant; thus, the evaluation of turbine performance at different water pressures is important for determining the sustainability of the dam body. Draft tube turbines run under high pressure and suffer from connection problems, such as vibrations and pressure fluctuation. Reducing the pressure fluctuation and minimizing the principal stress caused by undesired components of water in the draft tube turbine are ongoing problems that must be resolved. Here, we conducted a comprehensive review of studies performed on dams, powerhouses, and turbine vibration, focusing on the vibration of two turbine units: Kaplan and Francis turbine units. The survey covered several aspects of dam types (e.g., rock and concrete dams), powerhouse analysis, turbine vibrations, and the relationship between d...

The smart method of genetic programming (GP) is used to predict the operating pressure drop (ΔP s ) and the minimum spouting velocity u ms for conical spouted beds (CSBs) equipped with nonporous draft tubes. Accordingly, six dimensionless variables have been taken as model inputs, including crucial parameters associated with the bed and tube geometric and operating conditions. Two general correlations comprising almost all constitutive and operating variables have been derived for the first time by the GP approach. Both ΔP s and u ms values predicted by the GP technique are in a fair agreement with the values corresponding to the experiments, with average absolute relative errors This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record.

Dam and powerhouse operation sustainability is a major concern from the hydraulic engineering perspective. Powerhouse operation is one of the main sources of vibrations in the dam structure and hydropower plant; thus, the evaluation of turbine performance at different water pressures is important for determining the sustainability of the dam body. Draft tube turbines run under high pressure and suffer from connection problems, such as vibrations and pressure fluctuation. Reducing the pressure fluctuation and minimizing the principal stress caused by undesired components of water in the draft tube turbine are ongoing problems that must be resolved. Here, we conducted a comprehensive review of studies performed on dams, powerhouses, and turbine vibration, focusing on the vibration of two turbine units: Kaplan and Francis turbine units. The survey covered several aspects of dam types (e.g., rock and concrete dams), powerhouse analysis, turbine vibrations, and the relationship between d...

In turbine practice engineering, draft tube downstream running under extreme water flow pressure and velocity. This is causing a vibrations and pressure variation during different operation frequencies. The practical challenge of obtaining a stabilized water flow is ongoing domain of research. In this paper, a proposition of initiating submerged weir in the downstream of draft tube reaction turbine is inspected. The main goal of this research is to reduce the water flow pressure variation, velocity and shear distribution in accordance to the upstream water level influence. Two types of turbines including vertical Kaplan and Francis turbine units are examined. ANSYS CFX software tool is used to build three-dimension (3D) numerical models for the Kaplan and Francis turbines with building a submerged weir at the outlet of the draft tubes at three deferent height suggestions. The influence of the proposed submerged weir is studied the flow through these turbines by considering the dimensions of their components including the penstock with inlets, spiral casing, shafts and blades, and the draft tube with outlets. The findings of this research were tremendous proposition to solve the problem of negative pressure pulsation in draft tube of Kaplan and Francis turbines types.

Operating Francis turbine at part load is hindered by the flow instabilities developed downstream the runner, in the draft tube cone. The unsteady pressure field induced by the flow instabilities leads to vibrations. The paper presents the experimental investigations of the unsteady pressure field generated by the so-called vortex rope and its associated pressure fluctuations on the test rig available at Politehnica University Timisoara. The experimental measurements are performed without and with air admission in order to assess the control method. The unsteady pressure is recorded on four levels displaced along to the test section. As a result, the Fourier spectra without and with air admission are obtained in order to assess the air influence on the vortex rope parameters.

We introduce a quasi two-dimensional (Q2D) methodology for assessing the swirling flow exiting the runner of hydraulic turbines at arbitrary operating points, within a wide operating range. The Q2D model does not need actual runner computations, and as a result it represents a surrogate runner model for a-priori assessment of the swirling flow ingested by the draft tube. The axial, radial and circumferential velocity components are computed on a conical section located immediately downstream the runner blades trailing edge, then used as inlet conditions for regular draft tube computations. The main advantage of our model is that it allows the determination of the draft tube losses within the intended turbine operating range in the early design stages of a new or refurbished runner, thus providing a robust and systematic methodology to meet the optimal requirements for the flow at the runner outlet.

The water jet injection developed by Resiga et al. has been proved to be successful in mitigating the vortex rope and the corresponding pressure fluctuation. This method uses for supply of the jet, 10% from the flow discharge to eliminate the stagnant region, and this water is taken from upstream. Is not acceptable to bypass the runner with such a large fraction of the turbine discharge because of volumetric losses which appear into the system. The new flow-feedback control technique which has been implemented on the test rig of "Politehnica" University of Timisoara, take a fraction of the discharge from the draft tube cone wall, and redirects upstream to form an axial jet to mitigate the pressure fluctuations associated to the vortex rope. But from experimentally point of view the flow-feedback jet control discharge cannot be evaluated. This paper presents a method of determination of the discharge value based on velocity profiles match. Flow-feedback velocity profiles measured with Laser Doppler Velocimetry are going to be compared against profiles obtained using upstream, pump-generated-jet. A match of two velocity profiles will result in the same value of flow injected in case of flow-feedback and pump-generated-jet, respectively. In that way we can find the flow-feedback discharge.

The paper presents our experimental investigations into Francis turbine with low specific speed. First, the energetic and cavitational performances are computed based on experimental data recorded in hydropower plant. Next, the unsteady pressure is measured on the draft tube cone wall in order to identify the hydrodynamic instabilities at off-design operating conditions.

On EDF hydraulic production plants equipped with Francis turbines, there have been related some cases of significant pressure fluctuations detected in the upper parts of the penstock when units were operating in the high load pressure surge zone. There was no decrease of the Peak-to-Peak pressure fluctuations along the penstock in the upstream part as it could be expected. To understand the phenomenon, on site tests have been carried out using innovative non-intrusive dynamic pressure sensors in many points along the penstock allowing the analysis of upward and downward waves and their "interferences". These interferences cause in some cases standing waves for which the envelope of pressure oscillations along the penstock exhibits nodes and anti-nodes whose positions are relatively fixed along the penstock for a given operating point of the turbine. It appears that the ratio [Frequency of surge]/[Natural frequency of the penstock] conditions directly the number of nodes. This point is important because upper zones of the penstock close to the surge tank have generally not been designed to withstand high values of pressure fluctuations. For high number of ratio (3, 5, 7…), long term operation may induce mechanical fatigue of the penstock. A statistical approach was performed based on the dynamic signal databases of EDF and GE comprising data analysis of 21 occurrences of strong axial pressure surges of high load. It seems that certain values of the frequency ratio favour this resonance. This emphasizes the role of water exchanges between the rope and the penstock (complementarily with the draft tube) in establishing the conditions of resonance.

In this study, hydrodynamic characteristics such as the gas holdup (ε), the liquid phase velocity, and the mass transfer coefficient (k L a) for an air-diesel system were modeled for the bubble column (BCR), the airlift (ALR), and the airlift with the net draft tube (ALR-NDT) reactors at different superficial gas velocities ranging from 0.008 to 0.085 m s -1 . A 3D two-fluid Eulerian-Eulerian model was developed using the computational fluid dynamic (CFD) technique to model the three configurations of column reactors and predict the hydrodynamic parameters. The results of the 3D-CFD modeling showed good agreement with the experimental data where the average error was less than 14 and 9 % for ε and k L a respectively. Although the vortex occurred in BCR and ALR at high gas velocities, the optimum liquid and the gas circulation and distribution were observed in ALR-NDT. Furthermore, the formation of the dead zone (k L a = 0) in the reactors was studied, and the results revealed that ALR-NDT has a lower volume of dead zones (about 8 %) in comparison with BCR and ALR. In order to reduce the dead zone in BCR and ALR systems, the location of the gas diffuser and the draft tube was investigated. The dead zone was decreased by 12 % with shifting the gas diffuser to the bottom of the BCR. Also, by increasing the distance of the gas diffuser from the draft tube, the dead zone was decreased by 40 % specifically near the walls of ALR. Meanwhile, the simultaneous shifting of the gas diffuser and the draft tube to a lower position in ALR had no effect on the dead zone formation and its distribution.

A fluid bed dryer with inert particles was used for the drying of suspensions and pastes. The effects of the operating conditions on the dryer throughput and on the product quality were investigated. Experiments were performed in a cylindrical column 215 mm in diameter and 1200 mm in height with 0.925 mm diameter glass spheres as the fluidizing media. Cineb fungicide, copper hydroxide and pure water were used as the feed material. With respect to the main efficiency criteria, i.e., specific water evaporation rate, specific heat consumption and specific air consumption, a fluid bed dryer with inert particles represents a very attractive alternative to other drying technologies. A high drying efficiency results from the large contact area and from the large temperature difference between the inlet and outlet air. A rapid mixing of the particles, due to aggregative fluidization and mechanical agitation, leads to nearly isothermal conditions throughout the bed. In our experiments, suspe...

A model for predicting the particle circulation rate in a draft tube spouted bed dryer with inert particles is proposed and verified. The calculation algorithm requires three input values: the gas velocity in the draft tube one data point for the static pressure in the draft tube, and the pressure gradient in the annulus. The particle circulation rate can be estimated by solving the continuity and momentum equations for turbulent accelerating two-phase flow. The numerical solution is based on an iterative procedure until the assumed value of the particle circulation rate produces the prescribed value of the fluid static pressure at a certain axial position. Experiments were performed in a cylindrical column of 215 mm diameter with a draft tube of 70 mm diameter and length of 900 mm. Polyetylene pellets were used as the inert particles with a diameter of 3.3 mm, a density of 921 kg/m3 and a sphericity of 0.873. The model predictions of the particle circulation rate are in good agreem...

In recent times, optimization began to be popular in the turbomachinery field. The development of computational fluid dynamics (CFD) analysis and optimization technology provides the opportunity to maximize the performance of hydro turbines. The optimization techniques are focused mainly on the rotating components (runner and guide vane) of the hydro turbines. Meanwhile, fixed flow passages (stay vane, casing, and draft tube) are essential parts for the proper flow uniformity in the hydro turbines. The suppression of flow instabilities in the fixed flow passages is an inevitable process to ensure the power plant safety by the reduction of vortex-induced vibration and pressure pulsation in the hydro turbines. In this study, a CFD-based shape design optimization process is proposed with response surface methodology (RSM) to improve the flow uniformity in the fixed flow passages of a Francis hydro turbine model. The internal flow behaviors were compared between the initial and optimal ...

The synchronous pressure surge effect is a critical phenomenon occurring in Francis turbines operating at part load conditions. In this regime, pressure fluctuations are predominantly coming from the temporal rotation of a single helical vortex inside the turbine draft tube, called the part load vortex rope. However the combination of multi-physics interactions, geometry, cavitation, swirling flow and acoustic waves leads to a pressure amplification, called the synchronous pressure surge effect, which is more dangerous than the fluctuations resulting from the precessing vortex rope. While this subsequent amplification mechanism has been unraveled, the physical mechanism originating in the synchronous pressure wave remains poorly understood. We have therefore investigated the birth and the growth of the synchronous pressure wave in Francis turbines. By energy consideration of an azimuthal-temporal Fourier decomposition of the three dimensional numerical flow solutions in an axisymmetric draft tube geometry that is slightly disturbed at the wall, the source of the synchronous pressure and its amplification region are identified. In addition, the origin of this wave as the interaction of a wall disturbance with the part load vortex rope, is investigated using an asymptotic analysis and brings deeper comprehension of the synchronous wave generation mechanism.

A study has been conducted on the selection of a draft tube and its performance on a pilot scale conical spouted bed reactor used in the fast pyrolysis of biomass waste. The nonporous draft tube confers high stability to the bed and, furthermore, reduces the fluidizing agent flow rate, which means significant energy saving. The goal of the study is the optimization of the geometrical factors of the internal device in order to achieve suitable operating conditions, given that they have a great influence on bed hydrodynamics and, therefore, on heat transfer characteristics, residence time of the volatiles in the reactor and pyrolysis kinetics. The criteria for the selection are based on a compromise between gas flow rate and solid circulation rate in a bed operating under stable conditions. Moreover, studies have also been carried out on the performance of wood/sand mixtures and the critical elutriation diameter. The results show that a draft tube conical spouted bed operated with a suitable flow rate gives way to very good mixing, elutriation of light particles and short gas residence times.

The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine.

The shear rate is an important bioreactor parameter that needs to be evaluated due to its impact on microorganism morphology and viability, and consequently on bioproduct formation. Airlift bioreactors, classified as low-shear devices, are used as an alternative to conventional stirred-tank reactors. Considerable efforts have been made to characterize the shear environments in airlift bioreactors, using the average shear rate ( ̇𝛾av ) as a key parameter. However, there is no agreement among the values obtained in different studies, which can differ even in orders of magnitude. The methodologies used to obtain ̇𝛾av in the different studies could be the reason for the lack of agreement among them. In this work, ̇𝛾av in a concentric tube airlift bioreactor was evaluated using computational fluid dynamics (CFD), as well as based on universal velocity profiles for liquid flows in smooth pipes and annuli. Good agreement was obtained between the CFD-based average shear rates and the values obtained from universal velocity profiles, indicating that CFD simulation is a valuable tool for ̇𝛾av prediction. Airlift bioreactor • Average shear rate • Liquid velocity profile • Computational fluid dynamics List of symbols a Bubble-specific interfacial area (m -1 ) a b Area of all bubbles (m 2 ) A D ∕A R Downcomer-to-riser cross-sectional area ratio (-) A i Free area for fluid flow in region i of an airlift bioreactor (m 2 ) a i Bubble-specific interfacial area in region i of an airlift bioreactor (m -1 ) C 1 κ-ε Turbulence model constant (-) C 2 κ-ε Turbulence model constant (-) C κ-ε Turbulence model constant (-) * Alberto C. Badino

Francis type hydraulic turbine runners have complex blade shapes. Runner blades have three dimensional profiles that direct the incoming flow. In this study, a reverse engineering methodology is developed for the redesign of turbines. Traditional reverse engineering steps are combined with the basics and flow dynamics of hydraulic turbines and applied to two different turbine runners (which have different specific speeds) of two different hydroelectric power plants in operation. The methodology is first verified by application on the first runner and utilized for the redesign of the runner of another power plant. The reasons for the reduced performance of the second runner are examined with the help of the new inverse engineering design methodology and a rehabilitation study is performed. Thus, the runner which only provides 70% of its installed capacity, is redesigned and can now utilize its full capacity. Francis tipi su türbinlerine ait çark kanatlarının yapısı oldukça karmaşıktır. Üç boyutlu profilleri ile gelen akışı yönlendirirler. Bu çalışmada, türbinlerin yeniden tasarımı için bir tersine mühendislik yöntemi geliştirilmiştir. Geleneksel tersine mühendislik yöntemi, hidrolik türbin temel çalışma prensipleri ve akışkanlar mekaniği temelleri ile birleştirilerek iki farklı kullanımda olan santralin türbin çarkına (iki farklı özgül hızı olan) uygulanmıştır. Yöntem, öncelikle bir santrale uygulanarak doğrulanmış, ardından diğer santralin türbin çarkının yeniden tasarımında kullanılmıştır. İkinci santralin türbin çarkının çalışmasındaki sorunların sebepleri yeni geliştirilen yöntem ile araştırılmış ve çarkın rehabilitasyonu gerçekleştirilmiştir. Kapasitesinin %70'i verimle çalışan çark, tam kapasite çalışır hale gelmiştir.

Internal loop reactors and bubble columns are used extensively in the bio-and petrochemical industry. Simulation of these reactors has traditionally been based on dispersion and cell type models. For design and scaleup purposes however. these models are not adequate and more detailed knowledge of the flow structure within the reactors is necessary. This paper presents the results obtained from a two phase fluiddynamic model and how these results compare with experimental data. At ISCRE 11 a two fluid model based on a first principles approach was presented. To describe turbulence the single.phase k-E model was used. In this work a modified turbulence model based on the k-E structure is used. The model takes into account the turbulent kinetic energy and dissipation caused by interaction between the gas and liquid phases. Furthermore the basic two fluid model has been modified to take into account terms arising from the volume fraction fluctuations including pressure gradients. For experimental verification local gas fractions have been measured using the five point conductivity method. The system investigated is air/water. Measurements have been performed both for an ordinary bubble column and an internal loop reactor. both with largest inner diameter 0.288m. Furthermore the model results for axial liquid turbulent intensity and axial liquid velocity profiles are compared with experimental data available in the literature for an ordinary bubble column. The new turbulence model is shown to be a significant improvement over the single phase one previously used.

Ditioniti natrijuma i cinka (Na 2 S 2 O 4 i ZnS 2 O 4 ), poznati pod imenom hidrosulfiti, efikasna su redukciona sredstva koja imaju široku primjenu u raznim granama industrije . Najvažnija primjena natrijumditionita je u tekstilnoj industriji, te kao pomoćno sredstvo kod bojenja, štampanja i bijeljenja. U farmaceutskoj industriji koristi se pri sintezi nekih lijekova, u prehrambeboj industriji za bijeljenje sirupa voća, jestivog ulja te masti i želatina. Polazne sirovine za dobijanje ditionita su cinkov prah, SO 2 gas i Na 2 CO 3 . Ditioniti, Me 2 S 2 O4, MeS 2 O 4 su soli ditiosumporaste kiseline H 2 S 2 O 4 . koja nije izolovana u slobodnom stanju, zbog svoje velike nestabilnosti. Ključne riječi: natrijumditionit,sinteza, regulirajući faktori, cinkov prah, natrijumkarbonat. UVOD Natrijumditionit javlja se kao bezvodna so Na 2 S 2 O 4 , [1], molekulske teţine 174, i u obliku dihidrata Na 2 S 2 O4•2H 2 O, molekulske teţine 210. Zagrijavanjem dihidrata do 52 0 C u alkoholu on prelazi u bezvodni natrijumditionit. Sa povećanjem temperature rastorljivost im se povećava, [2]. Ako je u vodi prisutan natrijumhlorid ili natrijumhidroksid, rastvorljivost se naglo smanjuje. Natrijumditionit se karakteriše svojom nepostojanošću koja se povećava prisustvom vlage. Ovo razlaganje u odsustvu vazduha moţe se prikazati slijedećom jednaĉinom:

In this research our main objective is to design a elbow draft tube with varying diffuser angle and to find out the optimized model for the same or with enhanced diffuser angle. In order to enhance the design methodology as compare to the conventional draft tube design , we are adopting the simulation method to resolve the problem of draft tube design and to reduce the cost of prototyping and to get the improved results by using computational fluid analysis in ANSYS 14.0 by CFX solver. Aim is to be maximizing the pressure in the outlet of the draft tube. We have to take one factor to optimise the model of elbow draft tube in hydro power plant. The base paper experimental values are taken. Analysing of pressure and velocity contour in the previous results and our results will validate. The pressure contour and velocity contour taken are different diffuser angle.

Despite the increasing importance of airlift fermentors, very little published information is available on how the geometric configurations of the draft tubes and the air-sparging system affect the mixing and oxygen transfer characteristics of the fermentor. A 14-L airlift fermentor was designed and built with a fixed liquid height to diameter ratio of 1.5 utilizing four equally spaced air jets at the bottom. Two jet orifice sizes were used, 1.27 and 3.81 mm i.d., and for each jet size the following four geometric configurations were used: single inner concentric draft tube, single outer concentric draft tube, two concentric draft tubes, and no draft tubes where the fermentor was operated as a shallow bubble column. It was found that the presence of draft tubes stabilized liquid circulation patterns and gave systematically higher mixing times than those obtained in the absence of draft tubes. In addition, the double draft tube geometry resulted in higher mixing times than the single draft tubes. For the power per unit volume range 20 to about 250 W/m3 the larger 3.81-mm orifices gave systematically higher kLa values than the smaller 1.27-mm i.d. orifices. At 200 W/m3 the use of a single outer draft tube with the 3.81-mm orifices resulted in 94% increase in kLa value over that obtained with no draft tubes. However, the effect of draft tube geometry on kLa values when the 1.27-mm orifices were used was not significant. The air bubble formation characteristics at the jet orifices were found to be different, which reflected the differences observed in mass transfer and mixing characteristics. The power economy for oxygen transfer was found to depend strongly on the orifice size and less on the geometric configuration of draft tubes.

The pressure fluctuations of the turbines are caused by the swirl component in the draft tube, which is an undesired phenomenon that needs to be improved when the turbine operates in the off-design condition. In order to avoid these kinds of unsteady flow phenomena, a technology of J-Groove on the draft tube wall is investigated by numerical method. The validation test of performance is conducted to compare the result of numerical and experimental methods. The steady and unsteady state analyses are conducted to investigate the internal flow of a Francis hydro turbine model draft tube with and without J-Groove. The swirl flow in the draft tube is significantly suppressed by the J-Groove installation. Moreover, according to the unsteady state analysis, the amplitude of pressure fluctuation in the draft tube is reduced effectively by the J-Groove.

Suspension feedstock in high velocity oxy-fuel flame jets has opened a new area of research with great potential for advanced coatings. Understanding the suspension behavior in such a multidisciplinary process is a key factor in producing repeatable and controllable coatings. In this study, the effects of solid nanoparticles, suspended in liquid feedstock, on suspension fragmentation, vaporization rate and gas dynamics are investigated in the High Velocity Oxygen Fuel (HVOF) suspension spraying process by numerical modeling. The model consists of several sub-models that include pre-mixed combustion of propane-oxygen, non-premixed ethanol-oxygen combustion, modeling aerodynamic droplet break-up and evaporation, heat and mass transfer between liquid droplets and gas phase. Moreover, the thermo-physical properties of suspension (mixture of solid nanoparticles and liquid solvent) are calculated from theoretical models. The results show that small droplets carrying high nanoparticle concentrations develop higher surface tension and result in less fragmentation. The recommended ethanol droplet size at high nanoparticle loadings is found to be 50 μm due to the high evaporation rate in the mid-section of the nozzle. For larger droplets, severe fragmentation occurs inside the combustion chamber (CC) while complete evaporation takes place in the free jet region outside the gun.

While operating at part load, Francis turbines feature a precessing cavitation vortex rope in its draft tube. The precession of this vortex in the elbow of the draft tube acts as a pressure pulsation source which frequency can match the first hydroacoustic eigenfrequency of the hydraulic system in some cases. Resonance phenomenon can be predicted by using reduced scale physical model tests and numerical simulations, but it remains challenging. This paper proposes a procedure to estimate the risk of part load resonance at the early stage of a hydropower project. The proposed procedure uses the hydroacoustic properties of a given reduced scale physical model and applies them to a large number of turbine designs and power plant configurations to assess the risk of resonance for each one of them. Results show that resonance are likely to occur in hydropower plants in a certain range of turbine rated head and rated discharge values. These results can then indicate if more detailed investigations in some specific hydropower projects are necessary.

Hydropower plants may be required to operate in synchronous condenser mode in order to supply reactive power to the grid for compensating the fluctuations introduced by the intermittent renewable energies such wind and solar. When operating in this mode, the tail water in the Francis turbine or pump-turbine is depressed below the runner by injecting pressurized air in order to spin in air to reduce the power consumption. Many air-water interaction phenomena occur in the machine causing air losses and a consequent power consumption to recover the air lost. In this paper, the experimental investigation of the sloshing motion in the cone of a dewatered Francis turbine performed by image visualization and pressure measurements is presented. The developed image post processing method for identifying the amplitude and frequency of the oscillation of the free surface is described and the results obtained are illustrated and discussed.

Hydropower units may be required to operate in condenser mode to supply reactive power. In this operating mode, the water level in the turbine or pump-turbine is decreased below the runner by closing the guide vanes and injecting pressurized air. While operating in condenser mode the machine experiences power losses due to several air-water interaction phenomena which cause air losses. One of such phenomena is the sloshing motion of the water free surface below the runner in the draft tube cone of a Francis turbine. The objective of the present work is to experimentally investigate the sloshing motion of the water free surface in the draft tube cone of a reduced scale physical model of a Francis turbine operating in condenser mode. Images acquisition and simultaneous pressure fluctuation measurements are performed and an image processing method is developed to investigate amplitude and frequency of the sloshing motion of the free surface. It is found that this motion is excited at the natural frequency of the water volume and corresponds to the azimuthal wavenumber m = 1 of a rotating grav- ity wave. The amplitude of the motion is perturbed by wave breaking and it decreases by increasing the densimetric Froude number. The sloshing frequency slightly increases with respect to the natural frequency of the water volume by increasing the densimetric Froude number. Moreover, it results that this resonant phenomenon is not related to the torque perturbation.

The Pelton turbine is an impulse turbine typically installed for high head hydroelectric power plants. For a site with a rated head H and discharge Q, a higher specific speed turbine results in a more compact generating unit with reduced manufacturing costs but requires a larger number of jets. However, by increasing the number of jets and specific speed, the water jets tend to interfere, creating a significant energy loss. In the present research, the interaction between two adjacent jets in a six-jet Pelton runner is simulated using a GPU-accelerated particle-based in-house solver based on the 3-D Finite Volume Particle Method (FVPM). The numerical simulations are performed at eight operating points ranging fromN=N BEP ¼ 0:89 to N=N BEP ¼ 1:31; where N is the runner rotational speed, and BEP is the Best Efficiency Point. The torque and efficiency trends, as well as the speed range in which the jets interfere, are well-captured, which provides confidence in the use of the numerical simulations for the design optimization of Pelton turbines. The simulations, in particular, evidence a significant torque and efficiency drop at high rotational speeds, due to jet interference. Furthermore, jet disturbance yields load fluctuations at rotational speeds both lower and higher than the N BEP , which is likely to amplify fatigue damage. Both phenomena are worth considering that in the design process of a Pelton machine.

Th e article presents a case study on the Investigation of lateral vibrations in the turbine-generator unit 5 of the Inga 2 hydroelectric power plant in the Democratic Republic of the Congo. Lateral vibrations were experimentally determined using twelve proximity and eddy-current probes, positioned on each measurement plane. Th e results were analyzed using the Dasylab and R soft ware. Hence, it was observed that the vibration amplitudes of the upper guide bearing, lower guide bearing, and pivot/rotor exceeded acceptable or critical limit values of the international vibration standard for a rotating speed between 100-250 rpm. Th ese excesses can lead to rotor mass imbalances, the eccentricity of the rotor axis relative to the rotation axis of the shaft , and the deformation of the coupling shaft between the upper rotor shaft and the turbine rotor shaft. Subsequently, the means and the variances of the vibration amplitudes were evaluated and compared to the reference values of the international standard. Th e results of the compliance analysis revealed statistically signifi cant diff erences between the measured amplitudes and the reference values. Th us, it indicates deviations from international specifi cations.

The aim of the present paper is to investigate the vibrations that occur during the operation of a low power Banki turbine. The turbine was tested at different operating regimes in a laboratory installation, where it can operate with or without a variable load provided by a hydrodynamic brake coupled to the turbine shaft. Vibrations were measured on the turbine casing, on one of the turbine bearings, and on the brake. Dominant frequencies pertaining to each subassembly were identified. Measurements were also carried out with an added mass that simulates a piece of debris stuck inside the runner, causing an unbalance. The results obtained suggest that the bearings are a source of high frequency vibrations while relatively low frequency vibrations are caused by the turbine load. Very low frequency vibrations were also identified, which might be transmitted from the installation through the upstream pipe. The results underline the importance of vibration diagnostics to identify possibl...

A steady-state Actuator force model using the RANS equations is developed to calculate the power production and the flow through arrays of tidal or river Darrieus turbines. It uses detailed three dimensional force distributions depending on the position on the turbine, obtained beforehand by a set of blade-resolved URANS simulations of the turbine. New power coefficient and force coefficient laws depending on the local velocity instead of the upstream velocity are established and appear to be independent from the local turbine blockage in an array. Those laws are used to construct a model that adapt the Actuator force distributions to the local velocity of the flow reaching each turbine, in order to simulate each turbine functioning close to its maximum efficiency point. The model is validated against experimental measurements on a reduced-scale Darrieus turbine. A fence farm configuration and a two row farm configuration are investigated and compared to results of the same model adapted in two dimensions. The local blockage effect is more favorable for fences than for staggered turbine configurations, increasing the local velocity and the power production for each turbine.

Dam and powerhouse operation sustainability is a major concern from the hydraulic engineering perspective. Powerhouse operation is one of the main sources of vibrations in the dam structure and hydropower plant; thus, the evaluation of turbine performance at different water pressures is important for determining the sustainability of the dam body. Draft tube turbines run under high pressure and suffer from connection problems, such as vibrations and pressure fluctuation. Reducing the pressure fluctuation and minimizing the principal stress caused by undesired components of water in the draft tube turbine are ongoing problems that must be resolved. Here, we conducted a comprehensive review of studies performed on dams, powerhouses, and turbine vibration, focusing on the vibration of two turbine units: Kaplan and Francis turbine units. The survey covered several aspects of dam types (e.g., rock and concrete dams), powerhouse analysis, turbine vibrations, and the relationship between d...

З ростом обчислювальної механіки віртуальні гідравлічні машини стають все більш реалістичними, дають можливість визначити незначні деталі потоку, що в свою чергу неможливо отримати при тестуванні моделей. В данній роботі проведено 3D турбулентний аналіз реального потоку в радіально-осьовій гідравлічній турбіні при трьох відкриттях направляючого апарату та різній швидкості обертання за допомогою програмного забезпечення для обчислювальної динаміки рідин (CFD) Ansys CFX. Обчислюються для отримання характеристик потоку середні значення параметрів потоку, такі як швидкість і кути потоку на вході і на виході з робочого колеса, направляючого апарату і статору. Для поліпшення енергетичних показників на попередньому етапі проектування гідротурбіни проводиться чисельне моделювання потоку. Даний підхід CFD знижує витрати і час в порівнянні з експериментальними підходом і дає можливість удосконалити і аналізувати показники турбіни і її конструкцію до моменту виготовлення моделі. Розрахунковий комплекс програм надає можливість побачити картину розподілу тиску, поле векторів швидкості і руху частинок рідини для обґрунтування та аналізу результатів. Наведені результати розрахункового дослідження підтверджують, що гідравлічний коефіцієнт корисної дії гідравлічної турбіни в значній мірі залежить від втрат в напрямному апараті і робочому колесі і означає, що саме цим елементам варто приділяти найбільші увагу, їх конструкції та узгодженню потоку в них. Отримані розрахункові дані відповідають відомим раніше експериментальним рекомендаціям для високонапірної радіальноосьової гідротурбіни. Ключові слова: робоче колесо, спіральна камера, напрямний апарат, відсмоктуюча труба, статор, CFD, проточна частина, радіальноосьова гідротурбіна, характеристика потоку. К. А. МИРОНОВ, Ю. Ю. ОЛЕКСЕНКО, В. К. МИРОНОВ CFD ПОДХОД ДЛЯ АНАЛИЗА ХАРАКТЕРИСТИК ПОТОКА ВЫСОКОНАПОРНОЙ РАДИАЛЬНО-ОСЕВОЙ ГИДРОТУРБИНЫ С ростом вычислительной механики виртуальные гидравлические машины становятся все более реалистичными, дают возможность определить незначительные детали потока, что в свою очередь невозможно получить при тестировании моделей. В данной работе проведено 3D турбулентный анализ реального потока в радиально-осевой гидравлической турбине при трех открытиях направляющего аппарата и разной скорости вращения с помощью программного обеспечения для вычислительной динамики жидкостей (CFD) Ansys CFX. Вычисляются для получения характеристик потока средние значения параметров потока, такие как скорость и углы потока на входе и на выходе из рабочего колеса, направляющего аппарата и статора. Для улучшения энергетических показателей на предыдущем этапе проектирования гидротурбины проводится численное моделирование потока. Данный подход CFD снижает затраты и время по сравнению с экспериментальным подходом и дает возможность усовершенствовать и анализировать показатели турбины и ее конструкцию до момента изготовления модели. Расчетный комплекс программ позволяет увидеть картину распределения давления, поле векторов скорости и движения частиц жидкости для обоснования и анализа результатов. Приведенные результаты расчетного исследования подтверждают, что гидравлический КПД гидравлической турбины в значительной степени зависит от потерь в направляющем аппарате и рабочем колесе и означает, что именно этим элементам следует уделять наибольшее внимание, их конструкции и согласованию потока в них. Полученные расчетные данные соответствуют известным ранее экспериментальным рекомендациям для высоконапорной радиально-осевой гидротурбины. Ключевые слова: рабочее колесо, спиральная камера, направляющий аппарат, отсасывающая труба, статор, CFD, проточная часть, радиально-осевая гидротурбина, характеристика потока. K. MIRONOV, YU. OLEKSENKO, V. MIRONOV CFD APPROACH TO ANALYSIS OF THE FLOW CHARACTERISTICS OF A HIGH-PRESSURE FRANCIS TURBINE With the growth of computational mechanics, the virtual hydraulic machines are becoming more and more realistic to get minor details of the flow, which are not possible in model testing. In present work, 3D turbulent real flow analyses in hydraulic Francis turbine have been carried out at three guide vane opening and different rotation speed using Ansys CFX computational fluid dynamics (CFD) software. The average values of flow parameters like velocities and flow angles at the inlet and outlet of runner, guide vane and stay vane of turbine are computed to derive flow characteristics. To improve the energy performance at the preliminary design stage of the turbine, numerical flow simulations should be carried out. This CFD approach reduces costs and time in comparison with the experimental approach and makes it possible to improve and analyze turbine performance and its design before the model is manufactured. The computational complex of programs provides an opportunity to see the picture of pressure distribution, the field of velocity vectors and the movement of fluid particles for substantiation and analysis of results. The results of the computational study confirm that the hydraulic efficiency of a hydraulic turbine largely depends on the losses in the guide vane and the runner, which means it is these elements that should be given the most attention, their design and coordination of the flow in them. Analysis of the energy loss in the flow part of the Francis turbine was carried out using programs for calculating fluid flow in two-dimensional and three-dimensional formulation. The obtained calculated data correspond to the previously known experimental recommendations for high-pressure Francis turbine. The issues of increasing the energy performance of a projected high-pressure Francis turbine were considered.