Erosion Phenomena Research Articles

Climate Change Impact on the Stability of Soil Slopes from a Hydrological and Geotechnical Perspective

Climate change (CC) is expected to cause significant changes in weather patterns, leading to extreme phenomena. Specifically, the intensity of precipitation extremes is continuously escalating, even in regions with decreasing average precipitation levels. Given that CC leads to long-term shifts in weather patterns and may affect the precipitation characteristics (i.e., frequency, duration, and intensity) directly related to groundwater table fluctuations and soil erosion phenomena, it has the potential to significantly affect soil slope instabilities. In turn, slope stability and the structural integrity of nearby structures and infrastructure will be affected. Accordingly, the present paper focuses on the impact of CC on the geohazard of soil slope instability by considering both hydrological aspects, i.e., the impact on rainfall intensity on the groundwater table and the geotechnical aspects of this complex problem. The findings reveal that the impact of CC on potential slope instabilities can be detrimental or even beneficial, depending on the specific site and water conditions. Therefore, it is essential to do the following: (a) collect all the available data of the area of interest, (b) assess their variations over time, and (c) examine each potentially unstable slope on a case-by-case basis to properly mitigate this geohazard.

Oceanographic monitoring in Hornsund fjord, Svalbard

Abstract. Several climate-driven processes take place in the Arctic fjords. These include ice–ocean interactions, biodiversity and ocean circulation pattern changes, and coastal erosion phenomena. Conducting long-term oceanographic monitoring in the Arctic fjords is, therefore, essential for better understanding and predicting global environmental shifts. Here we address this issue by introducing a new hydrographic dataset from Hornsund, a fjord located in the southwestern part of the Svalbard archipelago. Hydrographic properties have been monitored with vertical temperature, salinity and depth profiles in several locations across the Hornsund fjord from 2015 to 2023. From 2016 onward, dissolved oxygen and turbidity data are available for the majority of casts. The dataset contributes to the so far infrequent observations, especially in spring and autumn, and extends the observations, typically concentrated in the central fjord, to the areas adjacent to the tidewater glaciers. Because sediment discharge from glaciers and land is an inseparable part of the glacier–ocean interactions, the suspended sediment concentration in the water column and the daily sedimentation rate adjacent to the tidewater glaciers are monitored with regular water sampling and bottom-moored sediment traps. Here we present the planning and execution of the monitoring campaign from the collection of the data to the postprocessing methods. All datasets are publicly available in the repositories referred to in the “Data availability” section of this paper.

Numerical Investigation of Wind Turbine Airfoil Icing and Its Influencing Factors under Mixed-Phase Conditions

Icing is a popular research area in wind energy, and the icing problem of the supercooled droplet–ice crystal mixed-phase condition is one of the new challenges. A numerical method for analyzing the icing characteristics of wind turbine airfoil under mixed-phase conditions is presented. The control equations for the dynamics of supercooled droplets and ice crystals are formulated using the Lagrangian method. Equations for the conservation of mass and energy during the icing process involving supercooled droplets and ice crystals are constructed. The impact of erosion phenomena on the mixed-phase icing process is examined, and methodologies for solving the control equations are introduced. The numerical method is utilized for modeling mixed-phase icing under a range of conditions. The results of these simulations are then compared with data obtained from icing wind tunnel tests to assess the validity of the method. The influence of various mixed-phase conditions on ice shapes is studied. It is found that higher icing temperatures correspond to a larger icing range and amount. The increase in supercooled droplet content, ice crystal content, and ice crystal diameter all contribute to enhanced ice accretion. However, the effects of ice crystal content and diameter are relatively minor.

ANÁLISE DO COMPORTAMENTO EROSIVO E CARACTERIZAÇÃO SEDIMENTOLÓGICA DA BARRA ARENOSA NA FOZ DO RIO ITABAPOANA, PRESIDENTE KENNEDY-ES

The state of Espírito Santo, despite being the smallest in the Southeast region, presents a significant diversity in the variations between the effects of retrogradation and coastal progradation. This dynamic is influenced by a complex interplay of variable factors, such as coastal geomorphology, hydrodynamics, and geology, which directly affect coastal cities and their development. The objectives of this study are to understand the phenomenon of coastal erosion and to analyze the morphological behavior of the sandy bar at the mouth of the Itabapoana River and at Praia das Neves, generating relevant information for the preservation of the coastal environment and minimizing material losses in urban areas adjacent to the sea. This work used tools such as the Ground Penetrating Radar (GPR) for the interpretation of radarfacies, as well as remote sensing and satellite image geoprocessing methodologies, combined with sedimentological characterization studies applied to Environmental Geology. The integration of GPR data revealed a complex sedimentary dynamic, with reflectors that indicate the progradation of beach deposits, as well as eolian, fluvial and marine influences, observing the presence of filled paleochannels and fluvial deposits. The analysis of satellite images allowed us to identify variations in the morphology of the beach and the location of the sandy bar at the mouth of the Itabapoana River, which shows migration patterns in a north-south direction. The compilation of the results suggests that coastal erosion in the region is cyclical, alternating between moments of progradation and retrogradation throughout the analyzed period, reflecting a complex coastal environment that involves climatic factors and marine and fluvial dynamics. The sediments analyzed were well selected, ranging from fine to medium fraction, with heavy fine sediments from the Araçuaí-Ribeira Orogen, showing low textural maturity.

Effect of Solid Particles in Polymer Waste Liquid on Grinding Tool Wall Erosion

Abstract With the continuous accumulation of polymer waste liquid in the third oil recovery process, the treatment of wellhead return waste liquid has become a key issue in oilfield exploitation and environmental protection. In this paper, the erosion failure of the cutter caused by sand-containing particles in the waste liquid during the shear grinding process is studied. The influence of the main structural parameters of the grinding tool and the erosion failure is studied by using the comprehensive numerical simulation method to reduce the erosion rate of the polymer flooding waste liquid on the cutter. Firstly, the flow field model of the solid-liquid fluid is established, and the erosion phenomenon on the tool wall is studied by combining the model with field experiments. In addition, the relationship between the different cutters structure and erosion rate of the grinding tool is studied, and the mathematical model is established. The optimized structural parameters are given to enhance the erosion resistance of the grinding tool in the process of polymer flooding wellhead waste liquid treatment and prolong its service life.

Tendance Evolutive Et Bilan Des Sediments De Profondeur De 2008 A 2018 : Cas De La Lagune Adjin (Littoral De La Cote D’ivoire)

The Adjin lagoon was studied in its morphological, hydrological and sedimentological aspect. This study made it possible to understand the morphological modifications of the bottom and surface of the Adjin lagoon based on the production and superposition of two bathymetric maps from the years 2008 and 2018. In addition, this study makes it possible to know the estimation of the speed, volume of sediments eroded and deposited. From a morphological point of view, the Adjin lagoon is characterized by depressions and shoals. The depressions are at the origin of the formation of “V” shaped channels. Shoals are characteristic of “U” shaped channels. Depths less than 11 m occupy 2/3 of its surface area. Particularly during the last ten years, the Adjin lagoon has suffered erosion and deposition phenomena. The rate of eroded sediments is estimated at approximately - 1.65 hm³ over an area of 7.9 km2 while in the same period, the rate of sediments deposited is +3.42 hm³ over an area of 12.3 km2 . This results in a sediment budget of +1.77 hm³. The evolutionary trend of sedimentary dynamics in the Adjin lagoon is therefore more favorable to fattening than to erosion. The sedimentation rate is estimated at approximately 2.7 cm/year. The morphological analysis and the sedimentary balance provide crucial information on the good management of fresh water and aquatic resources of the Adjin lagoon. Therefore, populations living near this body of water must limit their domestic activities in order to preserve the quality of this water

Integration of seasonal frequency domain electromagnetic surveys and geological data for assessing the integrity of earthen levee systems. The case study of the Panaro River (Northern Italy)

Floods rank among the most widespread and destructive natural hazards worldwide. The progressive degradation, impairment, and breach of earthen riverine levees can occur in both natural and anthropogenic environments, stemming from various scenarios or sequences of events. These may include hydraulic failure due to overtopping because of inadequate height, and structural failure occurring even prior to overtopping, due to insufficient geotechnical and hydraulic characteristics combined with external and internal erosion.Following the catastrophic flood of December 2020, caused by the collapse of a section of the levee system of the Panaro River (a tributary of the Po River, Northern Italy), local Authorities initiated a comprehensive investigation into the causes of the breach. Numerous factors, including geological, geomorphological, and ecological features, were found to have contributed to the progressive decrease of the levee integrity prior to and during the flood. This prompted a broader multidisciplinary study of the Panaro River levee system.The study expanded its focus to include the collapsed section (rebuilt in 2020), as well as an additional 30 km stretch of both the right and left levees north of Modena, totaling 60 km. Detailed geological and geophysical data were integrated into the analysis, with particular emphasis on evaluating the characteristics and integrity features of the levee system.This analysis was carried out using Frequency Domain Electromagnetic Methods (FDEM) on the top of the levees, previously calibrated using Electrical Resistivity Tomography (ERT), geological mapping, core logs, and Cone Penetration Tests (CPTs). The FDEM surveys were repeated in different environmental conditions, specifically in the dry 2021 summer season and in the wet 2023 spring season, during heavy rainfalls that caused disastrous floods in several areas of the Emilia-Romagna Region. Out of the 60 km surveyed in the study area, the comparison of the two datasets highlights an interval of about 4 km where the internal portion of the levees is characterized by relatively coarse-grained materials and higher permeability making it more prone to internal erosion phenomena. This paper describes and integrates the results of these investigations, drawing attention to the strengths and limitations of the FDEM method when applied to extensive surveys on earthen riverine levee systems. The proposed methodology contributes as well to maintenance and retrofitting efforts to reduce flood risk in the context of the present climate change scenarios.

Superhydrophobicity, Photocatalytic Self-Cleaning and Biocidal Activity Combined in a Siloxane-ZnO Composite for the Protection of Limestone.

The erosion phenomena of the natural stone in cultural heritage are induced by various sources. Consequently, the development of multifunctional protective materials that combine two or more useful properties is an effective strategy in addressing the synergistic effects of various erosion mechanisms. A multifunctional coating, consisting of a silane-based precursor and zinc oxide (ZnO) nanoparticles (NPs), is produced and tested for the protection of limestone. The hybrid coating combines the following three properties: superhydrophobicity, including water-repellency, photocatalytic self-cleaning and biocidal activity. The relative concentration of the NPs (0.8% w/w), used for the suggested composite coating, is carefully selected according to wetting studies, colourimetric measurements and durability (tape peeling) tests. The non-wetting state is evidenced on the surface of the composite coating by the large contact angle of water drops (≈153°) and the small contact angle hysteresis (≈5°), which gives rise to a physical self-cleaning scenario (lotus effect). The photocatalytic chemical self-cleaning is shown with the removal of methylene blue, induced by UV-A radiation. Moreover, it is shown that the suggested coating hinders the incubation of E. coli and S. aureus, as the inhibitions are 94.8 and 99.9%, respectively. Finally, preliminary studies reveal the chemical stability of the suggested coating.

Experimental investigation of collapsible soils under oedometric loading: effect of internal erosion

Collapsible soils, geological formations characterized by pronounced structural instability upon saturation, present a significant challenge in geotechnical engineering. This experimental study aims to deepen our understanding of the mechanisms governing the behavior of these soils, which are particularly prevalent in arid and semi-arid regions subject to extreme hydrological cycles. Collapsible soils, sensitive to climatic variability, undergo profound alterations in their hydromechanical properties due to alternating periods of prolonged drought and intense rainfall events. These fluctuations induce significant modifications in the soil's pore structure, promoting the development of internal erosion phenomena such as suffusion. The results obtained from this experimental investigation on reconstituted samples highlight the combined influence of various factors, such as water content, dry density, particle size, and flow rate, on the collapse potential. It appears that fine particles play a predominant role in the formation of fragile structures, susceptible to collapse upon saturation. Moreover, the intensity and duration of infiltration significantly influence the propagation velocity of ultrasonic waves, thus offering a promising tool for monitoring the evolution of damage within the soil mass. Furthermore, this study provides essential insights for assessing the risks associated with collapsible soils and contributes to the development of more reliable characterization and modeling methods. It emphasizes the need to consider the complex interactions between the physical, chemical, and mechanical properties of the soil, as well as the influence of environmental conditions, for better control of the risks associated with these materials.

Erosion of cultivated kelp facilitates dissolved organic carbon release

Growing trend of interests for contributions of cultivation of kelp to carbon sequestration have been driven globally. Saccharina japonica is an important cultivated seaweed, with erosion phenomenon usually occurs at the distal part of the frond in S. japonica throughout the growth cycle. However, the dynamics of dissolved organic carbon (DOC) release induced by erosion of S. japonica are not well understood. This study revealed that erosion induced a substantial increase in DOC release, with a 14% increase under low light (LL) conditions and a 54% increase under high light (HL) conditions. A 10 cm of long slit cut into the distal part of S. japonica increased the rate of DOC release by 56% under LL conditions, and by 13% under HL conditions. Additionally, the epibiotic microorganisms facilitate the release of DOC, and the effects were even more pronounced in erosive S. japonica. Conversely, the proximal part of S. japonica exhibited a higher photosynthetic carbon fixation capacity, with a carbon-to-nitrogen (C/N) ratio approximately 1.76 times higher than that in distal part. During the growth of S. japonica, excess photosynthetic products were often transported from the proximal part into distal part, further facilitating DOC release. In summary, DOC released induced by erosion of S. japonica could make contributions to oceanic carbon sequestration.

Research on wind turbine blade coating erosion modeling based on Generic modeling

Abstract In order to improve the accuracy of the prediction of the erosion phenomenon of wind turbine blade coatings, this study incorporates the wind-sand erosion data of wind turbine blade coating flat specimens obtained through wind tunnel experiments on the basis of the widely used generalized erosion model. A prediction model that accurately reflects the erosion and wear characteristics of wind turbine blade coatings is constructed using the least squares method. All the function parts included in the model showed favorable fitting effects, and the error between the model prediction results and the measured data was limited to a tolerable range. Therefore, the model has proved to be effective in predicting the erosion rate of wind turbine blade coating materials, which provides a solid theoretical foundation for the numerical simulation of the erosion and wear of wind turbine blades in a two-phase wind-sand flow environment.

Response of Surface Runoff Evolution to Landscape Patterns in Karst Areas: A Case Study of Yun–Gui Plateau

To control and improve the phenomena of rocky desertification and soil erosion in karst landform areas, which are caused by a series of human factors that include social and economic development and human activities, China has successively introduced many policies, resulting in spatial and temporal changes in the landscape pattern of the southern karst area. In this study, land use transfer intensity maps, the grid method, the sample line method, the semivariogram method, and the Spearman analysis method are used to explore the spatial and temporal evolutions in surface runoff as responses to landscape pattern and policy factors in karst landform area. Therefore, this study provides theoretical and policy support for improving the regional landscape structure, optimizing the landscape layout, introducing regional policies, reducing surface runoff, and alleviating soil erosion. The results show that the best scale for the study of landscape patterns in the southern karst area is 3000 m. Forests are the land type that make up the highest proportion in the southern karst area, and they have the strongest interception capacity for surface runoff. The spatial and temporal distributions of the surface runoff are significantly different, and urban expansion has led to an increase in impervious runoff year over year. Runoff is positively correlated with the Shannon diversity index (SHDI), patch density (PD), and landscape shape index (LSI). The stronger the landscape heterogeneity, the more runoff. DIVISION is positively correlated with forest runoff and negatively correlated with other land types. The higher is the degree of aggregation of impervious patches, the higher the regional runoff rate. The more dispersed the forest patches are, the smaller the area proportion, and the greater the runoff. In addition, policy factors have a significant impact on surface runoff.

Heat transfer and erosion control of nanofluid flow with tube inserts: Discrete phase model and adaptive neuro-fuzzy inference system approach

The current research explores the heat transfer and erosion phenomena in a tube employing newly designed inserts. Seven different geometries for the inserts have been developed into three dimensions. The fluid used is water with iron oxide nanoparticles and the flow regime is turbulent. The modeling technique involves a finite volume method with the Eulerian-Lagrangian framework incorporating a particle-scale erosion model. The outcomes indicate that raising the velocity and volume fraction of nanoadditives enhance both the heat transfer and erosion. In comparison to the scenario without fins, the heat transfer can be increased by approximately 8.07, 6.22, 18.03, 53.72, 45.21, 14.74 and 13.08 for the considered cases G1, G2, G3, G4, G5, G6 and G7, respectively. The specific geometric design of the inserts significantly influences the heat transfer and erosion in the tube, with geometry G4 showing the most substantial improvements in the heat transfer (approximately 53 %) and erosion (around 100 %) compared to a smooth tube. Factors such as velocity, particle size, fluid viscosity and insert shape affect the erosion in the tube with water demonstrating higher erosion rates than oil. The introduction of iron oxide nanoparticles leads to 2–3 times increment in the tube wall erosion. The erosion estimation on the tube wall has been performed using an adaptive neuro-fuzzy inference system artificial intelligence model with R2 = 0.981.

Assessing a transitional and turbulent overland flow resistance law for surfaces with different roughness

The control and management of soil erosion phenomena caused by rainfall and runoff is a significant issue in sloping landscapes, especially if they are scarcely or not vegetated. The study of the relationship between soil roughness and flow resistance is a fundamental step in improving the knowledge of erosion processes. In this study, the suitability of a theoretically deduced flow resistance law, based on a power-velocity profile, was assessed by transitional and turbulent overland flow data obtained in laboratory and available in the literature. These measurements were obtained in a sloping (slope in the range 1–40 %) rectangular flume, testing the effects of six different roughness conditions. At first, for each investigated roughness condition, the available measurements were used to calibrate and test the equation relating the Γ function of the velocity distribution, the flow Froude number, and the channel slope. For all the investigated conditions, this analysis allowed for demonstrating that the flow resistance law gives a reliable estimate of the Darcy–Weisbach friction factor, with errors ≤±5 % for 89.8–100 % of the examined cases with reference to the considered roughness condition. Then, using coefficients b (1.05) and c (0.562) of the Γ function available in the literature, the roughness effect was exclusively attributed to the a coefficient. In this case, the friction factor values calculated by the flow resistance law, with b = 1.05 and c = 0.562 and the a values corresponding to the different roughness conditions, are characterized by errors ≤±5% for 70.4–100 % of the cases. Finally, the power relationships between the calibrated a, b, and c coefficients of the Γ function, and Manning’s n values, corresponding to the roughness of the investigated surfaces, pointed out that the a coefficient is the most affected by the roughness conditions, as the exponent of Manning’s assumes the highest value. The significance of this research is due to the fact that a relevant issue in modeling overland flow is to define the resistance coefficient for variable roughness, especially the vegetated ones.

Assessment of a geomorphological-based design for coastal protection: The case of a wave-cut platform on the Bogliasco coast (Liguria Region, NW Italy)

Coastal erosion processes and the associated risks pose a significant challenge for coastal urban settlement administrations. Coastal managers are often seeking new approaches and solutions for coastal protection. Introducing protective structures such as breakwaters and groins often poses problems for management, e.g. modification of the natural panorama, changes within the local coastal dynamics and associated implications with regard to coastal hazards and risks. This paper describes a geomorphological-based approach to coastal structure design, taking as its study case the Bogliasco coast in the region of Liguria, near the eastern border of the municipality of Genova (Northwest Italy). Bogliasco is a stretch of rocky coast exposed to the most intense storms of the Liguria Sea and where the urban settlement reaches the edge of the cliff. To prevent cliff collapse and coastal flooding (and mitigate the associated risks), this study proposes an approach based on the structural recovery of an ancient wave-cut platform currently consumed by erosion. The recovered structure dissipates incoming waves, helping to mitigate both the erosive phenomena at the foot of the cliff and the risk of coastal flooding. The performance of the coastal protection project was evaluated by comparing the results of the XBeach model simulations for ante-operam and post-operam scenarios. The results indicate that the adopted solution contributes to a reduction of wave impact on the coast and the mitigation of flood hazards and risks. A geomorphological-based approach is therefore seen as a winning approach from both an engineering and management viewpoint.

Climate change and coastal erosion hotspots in West Africa: The case of Togo

Global warming is a worldwide phenomenon with disastrous implications ranging from ocean warming and glacier melting to sea level rise and coastal damage. This research assesses climate change trends, investigates coastal erosion hotspots and forecasts shoreline dynamics in West Africa. It also includes information on coastal erosion impacts and current coastal defence measures. The data set includes annual mean sea level anomaly, eddy kinetic energy, wave energy data and monthly climate data, such as precipitation, temperature, wind speed, and sunshine, from 1988 to 2023. Additionally, field survey data and Sentinel-2 satellite images were employed from 2015 to 2023 for coastal erosion monitoring. The Mann-Kendall test and Sen's slope test have been employed for climate trend analysis, while the DSAS tools have been used to identify coastal erosion hotspots and forecast future trends. The results revealed a significant increasing trend in annual sea level rise anomaly, annual wave energy, annual eddy kinetic energy, monthly temperature, and monthly sunshine. According to the shoreline dynamics investigation on Togolese coastal area, the Aflao-Port transect had significant accretion rates (up to 15 m/years), whereas the Port-Aneho transect experienced coastal erosion (up to −12 m/years). Climate change may increase wave energy intensity in certain regions, while coastal development can alter littoral transport and shoreline changes. Although there are soft and hard stabilisation solutions to counteract coastal erosion, such as groynes, sandbags, reforestation, and a series of nozzles in Togolese coast, the phenomenon of coastal erosion has evolved in recent years. Future projections in 2033 show that coastal erosion could move from 50 to 250 m inland. It is recommended that climate trend indicators, shoreline dynamics, and coastal stabilisation solutions be incorporated into all coastal and marine policies for sustainable management, with a view to ensuring minimal disruption to the ecosystem services provided by the sea and coast to people.

Butterfly valve erosion prediction based on LSTM network

When valves and pipelines are used, erosion wear is a major concern. Erosion wear can lead to equipment downtime, material replacement, and other issues, as well as seal surface failure. The research delves into the phenomenon of erosion in butterfly valves, crucial components utilized across diverse industrial sectors. Erosion primarily affects the valve's disc and seat regions, leading to premature wear and compromised performance. To address this issue, the research employs computational fluid dynamics (CFD) and machine learning techniques, including long short-term memory (LSTM) and BP neural networks, to predict erosion rates under various conditions (different valve openings and particle diameters). Results indicate that erosion escalates with time and larger valve openings, highlighting the need for proactive maintenance strategies. The LSTM model demonstrates superior predictive capabilities compared to the BP neural network, offering valuable insights for improving butterfly valve design and operational efficiency in industrial settings. Furthermore, to seek a more efficient network configuration, the intelligent search capabilities of the particle swarm optimization (PSO) algorithm have been utilized to systematically explore the optimal network structure parameters. The prediction results highlight the advantages of LSTM in handling time series data, particularly in predicting erosion rates with complex dynamic characteristics.

Effects of longitudinal profile shape on scour and flow resistance in rills

AbstractThe literature regarding how rill longitudinal profile (concave and convex) affects soil loss and flow resistance is still lacking. The only analysis available in the literature for rills is limited by the fact that measurements were performed for a unique mean slope value sp (18%). In this article, further rill measurements were conducted on a plot with sp = 15% and complex profile shapes and were used to widen the knowledge about the influence of longitudinal profile shape on rill scour, eroded volume, and flow resistance. The findings highlighted that the concave profile has a homogeneous spatial distribution of moderate scours, whereas the scours in the convex one are deeper and more confined, but they are not placed after the slope change as found for sp = 18%. The mean scour depth, which accounts for the discharge and profile shape effects, is not (concave) or is weakly (convex) related to the flow discharge. The concave profile determined a reduction of approximately 57% of the total eroded volume when compared with the convex profile shape, confirming that a concave hillslope limits erosive phenomena. Finally, the flow resistance equation guaranteed a precise estimation of the Darcy–Weisbach friction factor.

A New Numerical Method to Evaluate the Stability of Dike Slope Considering the Influence of Backward Erosion Piping

Backward erosion piping, a soil erosion phenomenon induced by seepage, compromises the stability of water-retaining structures such as dikes. During floods, the seepage in the dike body increases due to high water levels, which directly affects the progression of the piping channel. The formation of the piping channel then impacts the stability of the dike. In this paper, an improved piping model that considers the impact of seepage in the dike body is proposed based on Wewer’s model. Specifically, we added a seepage field of the dike body to the original model to account for the impact of dike-body seepage on the evolution of piping. The seepage field of the dike body is solved using Darcy’s law and the continuity equation for unsaturated porous media. In addition, this approach also incorporates the coupling effect of seepage stress. The accuracy of the model was verified through comparing the calculated results with the IJkdijk experiment and Wewer’s results. The effects of BEP on dike stability were investigated using the proposed improved piping model. The two major conclusions of the study are that (1) the incorporation of unsaturated seepage enhanced the performance of the piping model, allowing it to more accurately simulate the development of pipe length and the changing of pore pressure; and (2) the formation of the pipe impacted dike stability, leading to a substantial reduction in the safety factor of the dike slope.

Basic performance, cavitation and runaway investigations of a high specific speed Francis turbine with emphasis on cavitation analysis: A case study

The paper presents comprehensive experimental research on a high specific speed model Francis turbine with a characteristic runner diameter of 250 mm under the head of 12 m. Essentially, the turbine was designed for use at heads between 10 and 50 m, which are typical for installations with low specific speed Kaplan turbines. The basic performance, cavitation and runaway characteristics of the machine, which were determined as a result of the work, are quite rarely available in the literature in the case of high specific speed Francis turbines. The turbine achieved the maximum efficiency of 91%, kinematic specific speed of 82, and relatively wide operation range, so that it can be attractive as an alternative to the low specific speed Kaplan, semi-Kaplan or propeller turbines.In result of the basic laboratory tests, the performance characteristics of the machine operation in a wide range of guide vane opening angles between 9° and 36° as well as the shell efficiency characteristics were determined. On the characteristics plotted vs. rotational speed, the saddle effect was identified for the guide vane opening angles with values greater than the optimal one (22°). During the operation of the machine in the area of saddles, the change in the flow rate took quite surprising patterns. The share of the turbine thrust torque in the total torque was also determined, the characteristics of which are also burdened with a similar saddle effect.In the case of cavitation tests, a multi-aspect approach to cavitation diagnostics was used to characterize the cavitation phenomenon from the viewpoint of various criteria. Following this approach, the signals of the draft tube wall acceleration, acoustic emission at the draft tube cone upper flange, and pressure fluctuations inside the draft tube were used. The determined cavitation characteristics indicate little cavitation susceptibility of the Francis turbine blade system, despite the presented turbine having been designed to operate at higher flow rates than the classic high head Francis turbines with long interblade channels. The cavitating flow in the draft tube, directly below the runner, was also visualized during the cavitation tests. The paper presents the results of visualization for all cavitation states at five selected settings of the guide vane opening angle (two states in Partial Load, two states in High Load area and one state in the Best Efficiency Point), thanks to which it was possible to track the development of vortices during pressure reduction in the flow system.The runaway coefficient was determined as a result of the runaway tests. The value of 1.497 was reached at the optimum guide vane opening angle.Additionally, the work also presents in detail the efficiency scale effects to be expected at prototype turbines, i.e. those intended for operation at a higher head and with larger runner diameters. The efficiency of the machine with a runner diameter of 1.5 m and working at a head of 50 m reaches ∼93%. The influence of water viscosity on the change in efficiency of the prototype turbine is also shown.The presented methodology can be used for the proper selection of turbines intended for hydropower plants and for the proper installation of the runner in respect to the tailwater level in order to avoid the phenomenon of cavitation erosion.