Sediment erosion

Small hydropower (SHP) is a renewable, efficient and eco friendly technology. Out of all the essential civil components, the desilting tank is one of the most vital part of SHP schemes, which ejects the sediment and foreign particles carried by water through the conductor system and protects the hydro mechanical equipments. With the passage of time, the desilting device has undergone modifications and updation as per the choice of developer or the geological condition and economic constrains. In this paper, attempt has been made to review the different types of desilting devices being deployed in SHP plants in the Himalayan region.

Erosion is one of the major problems that restricts the lifetime of hydraulic turbines, especially the parts exposed to higher flow velocities. This paper presents a numerical simulation of erosion by solid particles entrained by the water flow through the components of a small Francis turbine. The computation of particle trajectories used our developed Lagrangian tracking code that considers random particle size and shape distribution and the effects of turbulence and near wall as well as the stator/rotor relative positions. As the impacts were predicted, a semi empirical erosion model was used to assess the mass erosion and the geometry degradation. The nature of the flow field in the runner of the investigated Francis turbine leads to a fluid-particle interaction more complex and strongly affecting the erosion patterns. The obtained results allow identifying the critical areas of erosion wear, where surfaces coatings are necessary to increase the lifetime for these sand laden water turbines. NOMENCLATURE A e Area of a surface element C D Drag coefficient C L Lift coefficient d Diameter Impact Normal Particle Radial Shear Tangential Axial At impact and rebound

Sediment constitutes several mineral compositions depending upon the geological formation and geography. In many of the rivers in Himalayas and Andes, Quartz is found as a main constituent (more than 50%), along with feldspar and other hard minerals. These particles have hardness more than 5 Moh's scale, which is capable to erode turbine components. In hydraulic turbines, flow is highly turbulent and unsteady, which can aggravate the erosion problems. Depending upon the nature of the flow, different components of turbines are eroded with different mechanisms. This chapter will provide a review on how various flow phenomena is responsible for particular types of erosion in turbines and their potential consequences. Some examples of the effect in existing power plants will be shown. This chapter will also discuss about some preventive measures that have been proposed and implemented to reduce the impact of the sediment particles in hydraulic machineries.

Guide vanes (GV) in Francis turbines are often reported to have a severe material erosion in case of sediments laden projects. A small clearance gap (CG) between GV wall and facing plate is allowed from the design to pivot GV as a part of flow regulating mechanism. Erosion in GV causes to increases the CG, which induces a leakage flow through the CG due to the inherent pressure difference between GV surfaces. Limited scientific studies on understanding the effects of the leakage flow from the eroded GV on turbine performance have been documented. Presented work aims to characterize the velocity conditions at the runner inlet of Francis turbine due to increase in the CG. Pressure and velocity measurements are done inside a GV cascade producing the similar velocity distribution as that in a reference prototype turbine. With a 2 mm CG, the relative velocity close to shroud of runner inlet is found to increase up to three folds of its nominal value. A vortex filament is found to be developed due to the mixing of the leakage flow with the main flow and is observed to pass into the runner with the flow.

In Francis turbine, a small clearance gap between the guide vanes and the cover plates is usually required to pivot guide vanes as a part of governing system. Deflection of cover plates and erosion of mating surfaces causes this gap to increase from its design value. The clearance gap induces the secondary flow in the distributor system. This effects the main flow at the runner inlet, which causes losses in efficiency and instability. A guide vane cascade of a low specific speed Francis turbine has been developed for experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. The setup is designed for particle image velocimetry (PIV) measurements from the position of stay vane outlet to the position of runner inlet. In this study, velocity and pressure measurements are conducted with 2 mm clearance gap on one side of guide vane. Leakage flow is observed and measured together with pressure measurements. It is concluded that the leakage flow behaves as a jet and mixes with the main flow in crosswise direction and forms a vortex filament. This causes non-uniform inlet flow conditions at runner blades. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Determination of sediment erosion and deposition fluxes from direct measurements associated with a drifting buoy in a tidal estuary, an application to the Seine (France). A direct evaluation of erosion and settling sediment fluxes, at the bottom boundary, is determined by measurements in a water column associated with a drifting buoy. The data were acquired during a high tide coefficient in the Seine estuary. The bed shear stress and the vertical sediment fluxes are regarded as independent variables. A new relation is proposed for calculating the total mass load of a given water column in a tidal estuary by knowing the friction velocity. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS sediment erosion / sediment deposition / sediment transportation / lagrangian coordinates Résumé-Une nouvelle méthode permettant l'évaluation directe des flux d'érosion et de dépôt de sédiments dans un estuaire macrotidal est proposée. Elle consiste à suivre les caractéristiques physiques, dont la charge solide, d'une colonne d'eau associée au déplacement d'une bouée dérivant dans l'estuaire de la Seine durant un cycle de marée de vive-eau. Cette démarche permet de considérer la contrainte de cisaillement sur le fond et le flux vertical des sédiments comme des variables indépendantes. Une relation entre la variation de la charge d'une colonne d'eau en matières en suspension et la vitesse de frottement sur le fond est suggérée. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS érosion de sédiment / dépôt de sédiment / transport sédimentaire / coordonnées lagrangiennes

Basically, the durability of hydraulic structures is heavily influenced by concrete surface resistance against mechanical wear. Hydro-abrasion is the term used to describe deterioration of concrete surface inflicted by the continuous removal of surface material due to the effect of water-dragged solids. This type of cumulative damage for the surface of concrete may be seen in practically all hydraulic systems, in varying degrees of severity. Essentially, such hydro-abrasive concrete wear reduces the life time of the hydraulic structure, and as a result of the maintenance necessary, the facility's nonoperation during the repair time increases costs. The numerical simulation was carried out according to the Messa device. Then, after an excellent agreement had been achieved with the experiments, a parametric study was implemented, where three key factors were investigated: the flow inclination angle, the density (sand concentration in water) and the rotational speed of the water. ANSYS 19.0 was used for simulating the erosion rate. According to the directed numerical simulation, the best flow inclination angle was at 45⁰, which showed lowest erosion rate. In addition, the findings showed that, the erosion rate raised considerably as the density and rotational speed increased.

Basically, the durability of hydraulic structures is heavily influenced by concrete surface resistance against mechanical wear. Hydro-abrasion is the term used to describe deterioration of concrete surface inflicted by the continuous removal of surface material due to the effect of water-dragged solids. This type of cumulative damage for the surface of concrete may be seen in practically all hydraulic systems, in varying degrees of severity. Essentially, such hydro-abrasive concrete wear reduces the life span of the hydraulic structure, and as a result of the maintenance necessary, the facility's non-operation during the repair time increases costs. The impact employed by the flow inclination angle, density (sand concentration in water), and velocity were studied in this work. The three various angles (30°, 45°, and 60°) different densities (35 and 45 kg/m3), and different velocities of 600, 900, and 1200 rpm were numerically determined using the program of ANSYS and the discret...

As a core component of a hydropower station, hydro turbines play a vital role in the integration of a power station. Research on the technology of hydro turbine is continuously increasing with the development of water electricity. On the basis of one-dimensional loss analysis, for three-dimension design, there are a lot of dimension of the internal flow passage shapes that are determined by experience. Therefore, the effect of the internal flow passage shapes on the performance and internal flow characteristics of a Francis hydro turbine model is investigated in this study. In this study, the small curvature of runner blade trailing edge shape is good for improving the efficiency of Francis turbine. The straight stay vane leading edge is good for suppressing the secondary flow. Moreover, suitable tongue passage shape and stay vane number improve the performance of the turbine considerably.

This study presents the performance characteristics of a small Francis turbine with an inline casing and is a continuation of a previous study. A new runner design has been implemented using the previous facility. The specific speed of the new runner has been modified from N s 80 to N s 100 m-kW-min-1. This turbine can be installed in a city water supply system. To dissipate excess pressures in the water line system an inline-turbine can be used instead of an inline-pressure reducing valve. Thus, some of the energy can be recovered by utilizing the pressure difference. For best applicability and minimal space consumption, the turbine is designed with an inline casing instead of a common spiral casing. As a characteristic of inline casing, the flow accesses to the runner are in the radial direction, showing low efficiency. The installation of vanes improves the internal flow and positively affects the output power. In contrast to the previous study, the new runner reduces the effect of the stay vanes by maintaining a higher efficiency.

This study addresses the problem of erosive wear of Francis turbine runner of a typical power station located in northern Himalayan belt of India. Wear damage is determined using the erosion models of IEC-2009, IEC-2013, empirical assessment of Thapa and a methodology proposed in this research work. The proposed model introduces effect of relative velocity of turbine instead of characteristic velocity and also the effect of curvature of the blades by incorporating a parameter referred to as geometrical factor. The results obtained from the proposed model of erosive wear of the Francis turbine have been calibrated against Jhimrukh Hydropower Centre(JHC). The study also includes petrographic analysis of the sediment taken from the site of power station to obtain the parameters related to concentration(C), size (K sz), hardness (K hd) and shape (K sh). Effect of these parameters have been introduced into the wear models used in this investigation. The erosive wear assessment reveals that damage is severe at the runner outlet due to the high relative velocity(45.5 m/s against 15.5 m/s at inlet) and presence of hard minerals. The average loss of thickness for runner is 1.3 mm/year of operation, which agrees within 10% of the measured values from site of the power station.

Reaction turbines basically Francis turbines and propeller/Kaplan turbines are suitable for medium and low head hydropower sites. The management of the small hydropower plants is an important factor, for achieving higher efficiency of hydro turbines with time. Turbines show declined performance after few years of operation, as they get severely damaged due to various reasons. One of the important reasons is erosive wear of the turbines due to cavitation. Reaction turbines, however are more prone to cavitation especially Francis turbines where a zone in the operating range is seriously affected by cavitation and considered as forbidden zone. Cavitation is a phenomenon which manifests itself in the pitting of the metallic surfaces of turbine parts because of the formation of cavities. In the present paper, studies undertaken in this field by several investigators have been discussed extensively. Based on literature survey various aspects related to cavitation in hydro turbines, different causes for the declined performance and efficiency of the hydro turbines and suitable remedial measures suggested by various investigators have been discussed.

Sediment erosion in hydraulic turbines has been a major challenge in development of hydropower projects in Nepal. The hard abrasive material present in the river water of this region cause rapid erosion of turbine components and affect the performance of turbines, which in turn decreases the efficiency, reliability and operating life of such projects. There is a need of a new design methodology to develop turbines to resist erosion in high sediment conditions. The first step towards such development would be to investigate different design options in laboratory, which needs a standard methodology to carry out sediment erosion test in controlled environment. This study is focused on design and development of a laboratory test setup suitable for carrying out sediment erosion test in Francis runner blades. A test rig called rotating disc apparatus has been developed and installed in Turbine Testing Laboratory, Kathmandu University, Nepal, which uses Francis runner blades as test specimens. The test carried out in this setup has shown that the Francis turbines designed with traditional design methodology is highly prone to loss of material due to sediment erosion.

Bhagirathi is a Himalayan River, which flows in Uttrakashi district in Uttarakhand state. It is one of the most important streams of the Ganga River. This river is famous for dam construction and fisheries development. The fishes of commercial importance in cold water are Mahaseer, Snow Trout. The fish production depends on the physical, chemical as well as biological qualities of water. In the present paper, water quality evaluation and dam in the sustaining fish population dynamics have been reviewed to make aware the fish culturist and environmentalist about the water quality factors which influence health of a pond and to increase the fish yields to meet the growing demands of present time scenario of the our country. The construction of dams causes many problems. Water quality and discharge of water from the dam wall systems also indirectly affect the fish populations. In this study, we also review some of the important impacts associated with dams and their recommended mitigation measures. There is a negative impact on fish population dynamics, especially for downstream habits due to dams. Water quality is measured like temperature, turbidity, carbon dioxide, pH, alkalinity, hardness, BOD, TDS, Turbidity. The maximum oxygen content of water was recorded in January 13.02 ± 0.166 mg l −1 and minimum 9.4 ± 0.05 mg l −1 in July in site I phase I (before the reservoir dam wall). While in site II and phase I (After the dam), the maximum DO was observed in the month of January of 12.1 mg l −1 and minimum in July of 8.93 mg l −1. This is because water level is minimized in site II almost dried in winter. The CO 2 of the Maneri Bhali phase I-Site I (before dam) was recorded maximum in April 3.10 ± 0.012 mg l −1. In Maneri Bhali phase I-Site II (After dam), the CO 2 was recorded maximum 3.01 ± 0.003 mg l −1 in the month July. The river of Garhwal Himalaya harbors a rich aquatic diversity, the most common endemic fish species that inhabit this fresh water is the Schizothorax species. The maximum no. of fish were observed in winter and minimum in monsoon. At present, the production of these fishes from the streams is very poor and is not well managed from recreational and conservation point of view. If such is developed properly, it can have revenue potential for our state government. Sports, fisheries, tourism should be promoted.

Bhagirathi is a Himalayan River, which flows in Uttrakashi district in Uttarakhand state. It is one of the most important streams of the Ganga River. This river is famous for dam construction and fisheries development. The fishes of commercial importance in cold water are Mahaseer, Snow Trout. The fish production depends on the physical, chemical as well as biological qualities of water. In the present paper, water quality evaluation and dam in the sustaining fish population dynamics have been reviewed to make aware the fish culturist and environmentalist about the water quality factors which influence health of a pond and to increase the fish yields to meet the growing demands of present time scenario of the our country. The construction of dams causes many problems. Water quality and discharge of water from the dam wall systems also indirectly affect the fish populations. In this study, we also review some of the important impacts associated with dams and their recommended mitigation measures. There is a negative impact on fish population dynamics, especially for downstream habits due to dams. Water quality is measured like temperature, turbidity, carbon dioxide, pH, alkalinity, hardness, BOD, TDS, Turbidity. The maximum oxygen content of water was recorded in January 13.02 ± 0.166 mg l −1 and minimum 9.4 ± 0.05 mg l −1 in July in site I phase I (before the reservoir dam wall). While in site II and phase I (After the dam), the maximum DO was observed in the month of January of 12.1 mg l −1 and minimum in July of 8.93 mg l −1. This is because water level is minimized in site II almost dried in winter. The CO 2 of the Maneri Bhali phase I-Site I (before dam) was recorded maximum in April 3.10 ± 0.012 mg l −1. In Maneri Bhali phase I-Site II (After dam), the CO 2 was recorded maximum 3.01 ± 0.003 mg l −1 in the month July. The river of Garhwal Himalaya harbors a rich aquatic diversity, the most common endemic fish species that inhabit this fresh water is the Schizothorax species. The maximum no. of fish were observed in winter and minimum in monsoon. At present, the production of these fishes from the streams is very poor and is not well managed from recreational and conservation point of view. If such is developed properly, it can have revenue potential for our state government. Sports, fisheries, tourism should be promoted.

In present work Computational fluid dynamics analysis based erosion wear prediction is performed for Francis turbine components, especially the runner. For the geometrical parameters, Francis turbine model with steady state condition and viscous flow turbulence SST model using ANSYS Fluent. The erosion effect on all the three component such as spiral casing, runner & draft tube has been studied for different concentration of sand particles from 1% - 6%. For each of those concentration the effect of variation in size has been studied for different sizes 10 ?m - 80 ?m. Further the effect of total erosion was also analyzed for different particle size. Erosion damage is found close to the upper and lower portions of the leading edge of the stay vane. some erosion spots at guide vane on the blade pressure side where suction side has minimum erosion. Maximum erosion damage observed on runner especially at the middle of the blade. The draft tube situated closer to runner having highest vel...

The operation of various types of turbomachines is importantly affected by sediment erosion. Francis turbines used for power generation typically suffer said effects due to the fact that they are used in sediment-laden rivers and are usually operated disregarding the long-term effect of the erosion on turbine performance. This investigation seeks to study the erosion rate for the main components of the turbines located at San Francisco hydropower plant in Pastaza, Ecuador. A sediment characterization study was performed in order to determine the properties of the particles present in Pastaza River and accurately predict their effect on the turbine flow passages. A numerical approach combining liquid–solid two-phase flow simulation and an erosion model was used to analyze the erosion rates at different operating conditions and determine wear patterns in the components. As expected, the results indicated that an increase in the erosion rate was obtained for higher intake flows. Howeve...

Acoustic signals can be used in various ways for suspended sediment monitoring. One possibility which lends itself particularly well in the context of hydropower plants (HPPs), is to use installations for acoustic discharge measurement (ADM). Such installations already exist at waterways of many HPPs. Similar to certain turbidimeters, the attenuation of the forward scattered signal travelling through the water-sediment mixture is correlated with suspended sediment concentration (SSC). This correlation can be based on reference SSCs, e.g. from gravimetric analyses of bottle samples. Without the need of additional sensors and practically maintenance-free, this method is used successfully in the HPP Fieschertal to warn the HPP operator of high SSC to prevent excessive turbine abrasion. Acoustic methods and systems that allow for estimating both SSC and particle size distribution (PSD) are under development. The simultaneous determination of SSC and PSD is not possible using a single frequency. Therefore, multi-frequency approaches are investigated for generally scattered signals. When backscattered signals are used, a stronger frequency dependency can be exploited. However, the reliable simultaneous determination of particle size (and distribution) and concentration is still a major challenge due to a low signal-to-noise ratio and an illposed problem of estimating concentration and size from recorded signals. The optimal setup configuration (angles, frequencies) for such a system is not unique and further investigations are recommended.

In present work Computational fluid dynamics analysis based erosion wear prediction is performed for Francis turbine components, especially the runner. For the geometrical parameters, Francis turbine model with steady state condition and viscous flow turbulence SST model using ANSYS Fluent. The erosion effect on all the three component such as spiral casing, runner & draft tube has been studied for different concentration of sand particles from 1% - 6%. For each of those concentration the effect of variation in size has been studied for different sizes 10 ?m - 80 ?m. Further the effect of total erosion was also analyzed for different particle size. Erosion damage is found close to the upper and lower portions of the leading edge of the stay vane. some erosion spots at guide vane on the blade pressure side where suction side has minimum erosion. Maximum erosion damage observed on runner especially at the middle of the blade. The draft tube situated closer to runner having highest vel...

Downward fluxes of organically rich biodeposits under suspended mussel lines can cause benthic impacts such as changes in benthic community structure or microbial mat production. Quantifying sediment erosion in these coastal ecosystems is important for understanding how fluxes of organic matter and mussel biodeposits contribute to benthic-pelagic coupling. Critical shear velocity (u*crit), erosion rates and particle size distributions of resuspended sediment were measured at four stations distributed along a transect perpendicular to a mussel farm in Lagune de la Grande Entrée, Îles-de-la-Madeleine (Quebec, Canada). Stations were selected underneath the outer-most mussel line (0 m) and at distances of 15, 30 m and at a reference station (500 m) further along the transect. Shear velocity was measured using a calibrated portable Particle Erosion Simulator, also referred to as the BEAST (Benthic Environmental Assessment Sediment Tool). Undisturbed sediment cores obtained by divers were exposed to shear stress to compare differences between stations. Erosion sequences indicated no significant differences in u*crit between stations, but there were significant differences in erosion rates beneath mussel lines compared to other stations. Erosion rates were the highest in cores from beneath mussel lines, but paradoxically had the lowest u*crit. Mean erosion rates at u*crit varied between 25 and Highlights ► An erosion device was used to quantify sediment near cultured mussels. ►Erosion rates were significantly higher beneath mussel lines. ►Critical shear velocities compared to other studies in eastern Canada ►The BEAST contributes to our understanding of benthic-pelagic coupling.

Draft tube is an important component of the hydraulic reaction turbine and affects the overall performance of turbine to a large extent. The flow inside the draft tube is complex because of the whirling flow coming out of runner and its diffusion along the draft tube. The kinetic energy coming out of runner is recovered in draft tube and part of recovery meets the losses. In the present work, the computational fluid dynamics (CFD) has been used for flow simulation in complete mixed flow Francis turbine for performance analysis for energy recovery, losses and flow pattern in an elbow draft tube used in Francis turbine at different operating conditions. The overall performance of the turbine at some typical operating regimes is validated with the experimental results and found to be in close comparison.DOI: http://dx.doi.org/10.3126/hn.v10i0.7103 Hydro Nepal Vol.10 January 2012 48-52

Guide vanes (GV) in Francis turbines are often reported to have a severe material erosion in case of sediments laden projects. A small clearance gap (CG) between GV wall and facing plate is allowed from the design to pivot GV as a part of flow regulating mechanism. Erosion in GV causes to increases the CG, which induces a leakage flow through the CG due to the inherent pressure difference between GV surfaces. Limited scientific studies on understanding the effects of the leakage flow from the eroded GV on turbine performance have been documented. Presented work aims to characterize the velocity conditions at the runner inlet of Francis turbine due to increase in the CG. Pressure and velocity measurements are done inside a GV cascade producing the similar velocity distribution as that in a reference prototype turbine. With a 2 mm CG, the relative velocity close to shroud of runner inlet is found to increase up to three folds of its nominal value. A vortex filament is found to be developed due to the mixing of the leakage flow with the main flow and is observed to pass into the runner with the flow.

Sediment erosion in guide vane of Francis turbine has been a crucial issue for turbines operating in Himalayas. Large sediment load with higher percentage of Quartz in Himalayan river causes erosion on GV faces, leaf, stem, leading and trailing edges and at clearance gaps (both facing plate and GV edges). This in turn increases profile roughness and clearance gaps height, causing higher friction losses and cross flow across the vanes, which ultimately affects inlet flow dynamics. Research attempts are limited to computational analysis and prediction of erosion losses. The effect of erosion on flow passing vanes is a crucial issue yet to be explored. This work focuses on experimental prediction of effect of erosion in 3GV cascade system. The cascade geometry was developed with CFD based iterative method, maintaining flow similarity around GV in turbine and cascade. It has been found that the pressure on two sides of vane and at vane outlet increases with erosion for considered extent erosion.

In Francis turbine, a small clearance gap between the guide vanes and the cover plates is usually required to pivot guide vanes as a part of governing system. Deflection of cover plates and erosion of mating surfaces causes this gap to increase from its design value. The clearance gap induces the secondary flow in the distributor system. This effects the main flow at the runner inlet, which causes losses in efficiency and instability. A guide vane cascade of a low specific speed Francis turbine has been developed for experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. The setup is designed for particle image velocimetry (PIV) measurements from the position of stay vane outlet to the position of runner inlet. In this study, velocity and pressure measurements are conducted with 2 mm clearance gap on one side of guide vane. Leakage flow is observed and measured together with pressure measurements. It is concluded that the leakage flow behaves as a jet and mixes with the main flow in crosswise direction and forms a vortex filament. This causes non-uniform inlet flow conditions at runner blades. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Opportunities of future hydropower developments in Asia comes with challenges of handling sediments in rivers. Hard minerals in flow causes turbine parts to erode with several undesirable effects. In Francis turbines, sediment erosion causes an increase of clearance gap between guide vane walls and cover plates. Due to inherit pressure difference between guide vane surfaces, a leakage flow arises from the clearance gap. A guide vane cascade is developed to study the characteristics of the leakage flow in a low specific speed Francis turbine. Velocity and pressure measurements are done at 80% of BEP flow as that in a reference prototype turbine. Cases with five different sizes of clearance gaps are investigated. Strong crosswise jet-like leakage flow is observed from the clearance gap. A vortex filament developed due to mixing of leakage flow with the main flow is found to hit the hub at runner inlet. The existence of a critical clearance gap size for which the leakage velocity and its effects are maximum is revealed. Interpretations of the experimental results show a close match with the observations of eroded turbine parts from a power plant.

Electricity is one of the most widely used forms of energy. Being a renewable source of energy small hydropower is considered as an environment-friendly and cheap source of electricity. The installation cost of the small hydropower project depends mainly on two parts-civil works and electromechanical equipment. One of the most important element on the recovery of a small hydro-power plant is the electromechanical equipment (turbine-alternator). The present paper intends to develop a correlation to determine the cost based on the cost influencing parameters as power and head using three different methods, namely; sigma plot method, linest method and logest method. An attempt has also been made to identify the best correlation among the three models closer to the actual cost of electro-mechanical equipment as collected from recently developed projects.

Mini hydropower is a tiny scheme of electricity generation for local area and also selling in national grid. In India it ranges from 101kW to 2000 kW renewable energy source. Proper maintenance of mini hydropower plants can decrease failure time and extend equipment life. The inappropriate maintenance is beginning of the rise in maintenance cost and cannot be cost effective to perform it repeatedly. Due to increase in the maintenance cost of turbine in Mini hydropower plants, an attempt has been made to develop the correlation for the maintenance cost of turbine by linear regression analysis with curve fitting tool in Matlab software, considering net head and capacity as cost influencing parameters. The developed correlation has been compared with the collected cost data of the existing hydropower stations for validation.

Hydro turbine machineries erosion due to silt is a complex issue for the effective practice of hydropower plants. Erosion caused by silt of the Pelton turbine buckets is a compound phenomenon that depends on size of silt particles , silt particles concentration , velocity of jet , and working time . This paper deals with the influence of silt erosion for various silt loaded factors and effective parameters. The preference selection index (PSI) and technique for order of preference by similarity to ideal solution (TOPSIS) approaches has been adopted to find optimal set of parameters which offers the highest performance for the Pelton turbine. Based up on the results obtained from both PSI and TOPSIS approaches it is found that optimal performance has been provided by A-1 alternate with geometric and flow parameters as , , and respectively.

Serious damage may occur to concrete hydraulic structures, such as water galleries, spillways, and stilling basins, due to the abrasive erosion caused by the presence of solid particles in the flow. This underlines the importance of being capable in providing characterization of the concrete from the point of view of its vulnerability to abrasive erosion, in order to improve the design of the structure and the material selection. Nevertheless, the existing apparatus for concrete abrasive erosion testing are either far from allowing realistic simulation of the actual environment in which this phenomenon occurs, or show a large degree of complexity and cost. An alternative method has been developed with the aid of Computational Fluid Dynamics (CFD). CFD was first employed to verify the effectiveness of a new laboratory equipment. Afterwards, a parameter has been introduced which, by successful comparison against preliminary experiments, proved suitable to quantify the effect of the fl...

Particle-laden flows such as pneumatic conveying or slurry transport are common in the minerals processing and oil sands industries. These industries face the challenge of erosion wear due to the repeated impact of the entrained particles, and subsequent damage to pipelines and equipment. Many economic losses such as equipment replacement cost, startup and shutdown cost, and loss in production are associated with this erosion wear.

More than a half of the overall power capacity in Ecuador uniquely depends on hydroelectric power, thanks to its geographical position and large water resources. Most of them use Francis turbines, which present detriment in their lifetime due to the presence of high hardness sediments in the water reservoirs located close to the Andean mountains. In order to mitigate such effect, a structured methodology, which identifies design space variables and defines parameters that governs the phenomenon is developed. The optimization is carried out through genetic algorithms formulated to determine optimal geometrical features and hydraulic parameters based on Euler meanline turbomachinery equation. The objective function for the optimization study at this preliminary stage was erosion factor, whilst the decision variables used were: outlet diameter, acceleration flow, degree of reaction and percentage of curvature deviation from a linear of the blade angle distribution. The results obtained showed that the erosion factor can be reduced by 49 % and that the relative flow velocity at the exit was a key optimization parameter to decrease the runner erosion. This great improvement at preliminary design has been compared with other similar studies, showing a good enough prediction of erosion and the capturing of the phenomena. Furthermore, the important contribution of the present methodology is the development of a simple and versatile tool to define the design space for erosion phenomena and in this way improve the lifetime of the blade turbine runner and hence decreasing maintenance costs.

The erosion of turbine components causes the decrease in turbine efficiency; increase in the maintenance cost and down time for turbine repair. All these factors contribute to the plant cost and cause the revenue losses. It is, therefore, essential to study the amount of efficiency loss owing to the erosion of turbine components due to the silt particles coming in water. The present study has been carried out to investigate the effect of silt erosion for different silt laden parameters and operating parameters such as silt concentration, size of silt particles, jet velocity and operating hours of the turbine on efficiency loss in Pelton turbine buckets. It has been found that turbine efficiency loss depends strongly on silt and operating parameters. A correlation has also been developed as a function of silt parameters and operating condition for percentage of efficiency loss. The developed correlation may be useful for turbine manufactures in order to predict the efficiency loss of a Pelton turbine at the manufacturing stage of a turbine under a given silt content water for a particular site.

In the present study, an experiment was carried out to investigate the mechanism of erosion of a small scale Pelton turbine, under actual flow conditions. Samples of silt were collected from the head work of one of the most silt affected hydro power station in India. Silt parameters (silt particle size and silt concentration) were considered to investigate the mechanism of silt erosion on Pelton turbine buckets for different silt sizes. In the first part of the experimentation, hot spots (spots which are more prone to erosion) were identified under a high silt concentration. Second part of the experimentation was carried out to study the erosion mechanism for small specimens of metal which were fixed at the marked hot spots. Based on the investigation, it has been found that silt size is a strong parameter to produce erosion and the material removal from the surface is due to plastic deformation and ploughing of surface.

The Vishnugad Pipalkoti HydroElectric Project (VPHEP) is a run-of-river-project planned to be located on the Alaknanda River in the western Himalayas. The Alaknanda River carries a high sediment load primarily consisting of quartz which has a high potential for eroding the hydro-mechanical parts of the project. In this paper a simple approach to optimizing the sediment handling of the scheme is presented. This approach is based on an economical balance of capital costs, maintenance costs and revenue loss due to the anticipated downtime in connection with repair work and the loss of storage and thus ability to store water from off-peak to peak hours. Mathematical modeling and desk studies have been used to estimate the costs and revenues.

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...

Pelton turbine is commonly employed high head impulse type turbine. Pelton turbine injector is an integrated part of the Pelton turbine machine which serves the purpose of converting entire pressure energy of water to kinetic energy and also regulates the water flowrate, with partial opening hence governing the power production. Severe erosion in Pelton turbine injector is reported from field setting research studies. Since the jet is atmospheric pressure jet, there is few chances of occurrence of cavitation hence it can be understood that impact of sand particles is the major cause of erosion. Furthermore, with turbine operating in partial flow condition, more erosion is reported in the needle of injector. For a long spear type injector, this study explores the cause of erosion by modeling the motion of the sand particle flow in steady state jet. For numerical modeling of the flow, the realizable k-epsilon model is used and for modeling the particle flow, the Discrete Phase Model (...

Draft tube is an important component of the hydraulic reaction turbine and affects the overall performance of turbine to a large extent. The flow inside the draft tube is complex because of the whirling flow coming out of runner and its diffusion along the draft tube. The kinetic energy coming out of runner is recovered in draft tube and part of recovery meets the losses. In the present work, the computational fluid dynamics (CFD) has been used for flow simulation in complete mixed flow Francis turbine for performance analysis for energy recovery, losses and flow pattern in an elbow draft tube used in Francis turbine at different operating conditions. The overall performance of the turbine at some typical operating regimes is validated with the experimental results and found to be in close comparison.DOI: http://dx.doi.org/10.3126/hn.v10i0.7103 Hydro Nepal Vol.10 January 2012 48-52

In any hydro power plant its turbine enacts a major role in deciding the competence as lot of phenomena depends on it if turbine works smoother then performance achieved by plant will be more and for that analysis of turbine becomes a need of the time and this need is fulfilled by the CFD it offers various software packages to analyse the part numerically at virtually no cost and in this study various parameters affecting different component of Francis turbine are analysed using CFD in addition to some validation of CFD results with actual one are also mentioned.

Hydropower, large and small, remains by far the most important of the renewable sources for electrical power generation worldwide, providing 19% of the planet's electricity. Small hydro is one of the cost-effective and environmentally benign energy technologies to be considered for rural electrification in less developed countries. The installation cost of the small hydropower project is mainly divided into two parts-Civil works and electromechanical equipment. One of the most important element on the recovery of a small hydro-power plant is the electromechanical equipment (turbine-alternator). The cost of the equipment means a high percentage of the total budget of the plant. The present paper intends to develop a correlation to determine the cost based on the influencing parameters such as power and head. An attempt has been made to develop the trend of the cost of electromechanical equipment with the increase in head of the hydropower plant.

Mini hydropower is a tiny scheme of electricity generation for local area and also selling in national grid. In India it ranges from 101kW to 2000 kW renewable energy source. Proper maintenance of mini hydropower plants can decrease failure time and extend equipment life. The inappropriate maintenance is beginning of the rise in maintenance cost and cannot be cost effective to perform it repeatedly. Due to increase in the maintenance cost of turbine in Mini hydropower plants, an attempt has been made to develop the correlation for the maintenance cost of turbine by linear regression analysis with curve fitting tool in Matlab software, considering net head and capacity as cost influencing parameters. The developed correlation has been compared with the collected cost data of the existing hydropower stations for validation.

Francis turbine operating in sediment laden river projects, excessive wear and damage often occurs on the guide vanes, facing plates, runner and labyrinth rings due to sand erosion. The requirement of dismantling the head cover to repair the facing plates and wearing ring is one of the major influencing parameter of turbine assembly design to increase down time during turbine maintenance. This article discusses on standard assembly design of head cover for vertical Francis turbine installed in Nepalese hydropower station, including its effect on unit outage during overhauling of the machine. Design optimization of head cover has been carried out by considering the maintenance performance analysis tool, intending to explore the ease of maintenance and to identify the maintenance friendly assembly design of vertical Francis turbine.

Opportunities of future hydropower developments in Asia comes with challenges of handling sediments in rivers. Hard minerals in flow causes turbine parts to erode with several undesirable effects. In Francis turbines, sediment erosion causes an increase of clearance gap between guide vane walls and cover plates. Due to inherit pressure difference between guide vane surfaces, a leakage flow arises from the clearance gap. A guide vane cascade is developed to study the characteristics of the leakage flow in a low specific speed Francis turbine. Velocity and pressure measurements are done at 80% of BEP flow as that in a reference prototype turbine. Cases with five different sizes of clearance gaps are investigated. Strong crosswise jet-like leakage flow is observed from the clearance gap. A vortex filament developed due to mixing of leakage flow with the main flow is found to hit the hub at runner inlet. The existence of a critical clearance gap size for which the leakage velocity and its effects are maximum is revealed. Interpretations of the experimental results show a close match with the observations of eroded turbine parts from a power plant.

The aim of this study was comparative analysis of sediment-induced erosion on optimized design and traditional design of Francis runner blade. The analysis was conducted through laboratory experiments in a test rig called Rotating Disc Apparatus. The results showed that the extent of erosion was significantly less in the optimized design when compared based on the material loss. It was observed that the optimized design could reduce sediment erosion by about 14.4% if it was used in place of the reference design for entire duration of the experiment. Based on the observations and results obtained, it has been concluded that the optimization of hydraulic design of blade profile of Francis runner can significantly reduce the effect of sediment-induced erosion.

Hard sediment particles as quartz are present in high amount in the rivers across Asian and Andes mountain ranges. This cause the runoff river hydropower plants in these regions to suffer from erosion wear. The hydro turbine components erode severely during the monsoon periods. Due to high relative velocity the turbine runners are more vulnerable. Loss of turbine efficiency and high cost of repair and maintenance are the major consequences of the erosion. Several attempts including surface coatings to control the sediment erosion in Francis runners have not shown satisfactory results. One of the emerging solutions is to reduce the relative velocity inside the runner by improving the hydraulic design. This includes optimization of the runner blade profile to reduce sediment erosion, while avoiding cavitation and still maintaining the highest possible efficiency. This study has been conducted to identify the alternative blade profiles of high head Francis runners and estimate the effects of sediment erosion on each new profile. A new design program named as "Khoj" has been developed to facilitate this study. The program can generate the profiles of Francis runner based on the traditional equations. It is also capable to export the designs for CFD and FEM analysis. Erosion factor has been defined as a means to compare the relative change in sediment erosion due to the variation of the runner design. A reference turbine has been established and alternative blade profiles have been designed. CFD analysis has been conducted to evaluate the performance of the alternative designs relative to the erosive conditions of the reference turbine. It has been observed that the shape of runner blade has a significant effect on velocity distribution and hence on the sediment erosion of the runner. Results of CFD analysis validates prediction from the design program that the blade profile with higher blade loading at inlet can reduce the sediment erosion in runner up to 33%. It was also observed that this condition improves the runner efficiency without any change in the runner main dimensions. Results of this study can be useful to design Francis turbines operating in sediment conditions.

Hydro turbine machineries erosion due to silt is a complex issue for the effective practice of hydropower plants. Erosion caused by silt of the Pelton turbine buckets is a compound phenomenon that depends on size of silt particles , silt particles concentration , velocity of jet , and working time . This paper deals with the influence of silt erosion for various silt loaded factors and effective parameters. The preference selection index (PSI) and technique for order of preference by similarity to ideal solution (TOPSIS) approaches has been adopted to find optimal set of parameters which offers the highest performance for the Pelton turbine. Based up on the results obtained from both PSI and TOPSIS approaches it is found that optimal performance has been provided by A-1 alternate with geometric and flow parameters as , , and respectively.

This thesis has been prepared with the support and supervision of many people to whom I would like to express gratefulness. Primarily, my deepest appreciation is for my promoters Prof. Jean Berlamont and Prof. Patrick Willems who kindly have shared their expertise with me and have provided their precious and enlightening guidance and help to me enabling me to undertake this research throughout the last few years. Subsequently, I would like to express my sincere gratitude to Prof. Alberto Campisano who very kindly has accepted to help me in doing the numerical investigations for sediment transport analysis, which has contributed enormously to this thesis, and for his valuable assessments and advices that helped me ameliorate my thesis. Moreover, I would like to extend my deep gratefulness to Prof. Jan Feyen and Prof. Jaak Monbaliu for their many constructive remarks and feedbacks which highly contributed to the refinement and improvement of my thesis. In addition, I would like to thank Prof. Willy Bauwens for his precious assessments and comments that enabled me improve my thesis. I am also grateful to Keramo-Steinzeug Co. in Belgium for having provided the Giehl type flushing tank to the Hydraulics Laboratory of this university, which was fundamental to this research. Also, much appreciation goes to Innovyze Co. in the UK (which was previously known as MWH Soft, and on beforehand as Wallingford Software) for providing the InfoWorks CS license to our laboratory, which facilitated my research with urban drainage systems. I extend my gratitude to Prof. Carlo Modica, Dr. Guido Vaes, Dr. Enrico Creaco, and Raf Bouteligier for their counsels and assistances in various forms that helped me accomplish this research in a smoother way. Also, I would like to thank Mr. Luc Willems for his assistances in performing the laboratory experiments for testing the Giehl flushing tank. Besides, I am indebted to Dr. Toon Goormans who always provided valuable feedbacks and hints to me whenever we were discussing the hydraulic issues in our office and for his helpful assistances with MATLAB. I also would like to thank all my colleagues in the Hydraulics Laboratory of the Civil Engineering Department for their enjoyable company in the years I have been doing this research over there. Last but not least, I would like to express my deepest appreciation to my beloved family, my father, my mother, my sister and her family, and my uncle for their priceless supports and encouragements ii throughout all these years and for being so patient to let me finalize this research. Also, many thanks to all my friends whose amiable support gave confidence to me and encouraged my progress.

A numerical investigation to simulate the cleaning effects of successive flushes over sediment beds in prismatic channels is presented in this paper. The 1D De Saint Venant-Exner equations were used to describe the temporal evolution of the sediment bed after each flush. The predictive capacity of two sediment transport formulae was explored against experimental results from laboratory tests. Results show that the adopted model can successfully describe the evolution of the sediment bed due to the flushes exerted during the experiments, with differences between the used transport formulae depending on the channel invert slope and on the flush energy.

Erosion of hydro turbine components through sand laden river water is one of the biggest problems in the Himalayan region. This problem exists for all kinds of turbines. Apart from erosion of buckets, erosion was also observed in nozzle of the Pelton turbines due to sand particles and such problem was observed in 22 MW Chilime Hydropower Plant in Nepal. Detailed studies were conducted and erosion analysis was carried out in this case study. Sieve and mineral content analyses were systematically carried out and sediment load was calculated. By doing this, erosion rate and efficiency reduction were established using already known methodology and scenario for similar hydropower plants. The flow analysis through surface of needle was established by drawing flow net diagrams. This detrimental damage led to efficiency reduction of 1.21% consequently resulting in loss of power generation. A wear rate of 3.4 mm/year was estimated for the needle and the bucket after a systematic analysis.