Simone Pagliara

Last Name

Pagliara

First Name

Simone

ORCID

0000-0002-9939-8930

Organisational unit

03820 - Boes, Robert / Boes, Robert

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Publications 1 - 10 of 17

Analysis of fish migration in correspondence with wood and rock-made instream structures
Kurdistani, Sahameddin M.; Pagliara, Simone; Palermo, Michele (2023)
Geomorphology
Anthropic exploitation of soil, forests, and water bodies contributes to the modification of river flow regimes and sediment transport dynamics, thus affecting fish habitats and water quality. In the last decades, the increasing awareness of the consequences of such modifications on natural contexts has stimulated researchers and practitioners to provide more innovative solutions aiming at enhancing river biodiversity. Recently developed eco-friendly approaches for river restoration evidenced the necessity of more careful planning and management of natural resources, including the maintenance and enhancement of fish species' habitats. The present study aims at assessing the interaction of different types of wood- and rock-made instream structures with river flow regimes and habitat requirements of many freshwater fish species, accounting for the influence of downstream scour potholes to facilitate fish species migration and spawning. Experimental tests showed that instream structures cause deep scour holes characterized by low flow velocity zones, thus decreasing the required fish swimming power and potentially providing suitable conditions for the migration of freshwater fish species. Using dimensional analysis, empirical relationships were derived to optimize the longitudinal distance between subsequent instream structures, accounting for the effects of various structure geometries and fish biological characteristics. Nevertheless, further investigation is needed to validate the proposed relationships at prototype scale. This study ultimately contributes at providing tools to design river instream structures favorable to fish migration.
Aerated Flows in Low-Level Outlets with Varying Geometry and Roughness
Pagliara, Simone (2025)
VAW-Mitteilungen
Reservoir dams play a crucial role in modern society, supporting hydropower production, irrigation, water supply, and flood protection. Low-level outlets (LLO) are key safety elements of large dams, allowing fast reservoir drawdown during emergencies or maintenance works. LLOs typically consist of a pressurized tunnel, a gate chamber with gates, and a free-surface outlet tunnel which conveys the resulting high-velocity flows. These high-velocity, highly turbulent flows generate sub-pressures in the gate chamber, resulting in challenges such as cavitation and gate vibration, while the combination with high sediment loads may induce hydro-abrasion. Adequate aeration through an air vent mitigates these issues. However, current design guidelines are inconsistent, with air demand data from model studies and prototypes exhibiting scatters of up to two orders of magnitude. To address this gap, this study conducted large-scale physical model experiments at the Laboratory of Hydraulics, Hydrology, and Glaciology (VAW), ETH Zürich, to investigate air demand, flow patterns, and air-water flow properties in LLOs. The study began with the development of a methodology to validate dual-tip conductivity probes for measuring air-water flow properties. These probes reliably measured interface velocities and chord lengths of individual bubbles advected in an upwards water flow across a wide range of bubble sizes and velocities, enabling their confident application for the subsequent investigations. First, the effect of wall roughness, a characteristic of LLOs influenced by material choice and wear, on high-velocity air-water flows was systematically evaluated. Findings revealed that wall roughness significantly influenced flow characteristics, increasing mixture flow depth and air entrainment while reducing flow velocity. Air demand increased with greater wall roughness, and a design equation was proposed. The investigation ultimately highlighted the necessity of accounting for wall roughness and the corresponding hydraulic regime when highvelocity air-water flows are involved. Then, the influence of tunnel lateral profile transitions, common in prototype LLOs, was assessed. Three lateral profile transitions (i.e., an abrupt transition and two gradual transitions of varying lengths) were analysed, showing a significant impact on shockwave patterns and air demand, leading to the derivation of novel empirical design equations. Finally, the study focused on bottom aerators, typically used in spillways to mitigate cavitation risk, but under-researched for LLOs. Their influence on air demand, flow patterns, and airwater flow properties were systematically evaluated, resulting in updated empirical design equations. These findings demonstrated the viability of using bottom aerators in LLOs, and established the foundations for developing comprehensive design guidelines. Ultimately, the present work significantly advanced the physical understanding of high-velocity air-water flows, and provided design guidelines for the safe design and efficient operation of low-level outlets.
Scour Features due to Inclined and Curved Rock Sills at River Bends
Mahmoudi Kurdistani, Sahameddin; Palermo, Michele; Pagliara, Simone (2024)
Journal of Irrigation and Drainage Engineering
Rock-sills are instream low-head structures generally used to stabilize the riverbed. Their presence causes the formation of pools and riffles along the river, thus improving the aquatic habitat and creating resting spots for aquatic species. In this study, the riverbed morphology due to the rock-sill configuration installed at river bends was experimentally analyzed under clear-water condition, with a uniform, granular bed material. Tests were conducted by varying the inclination of sills with respect to the radial direction in three curved bends. Experimental evidence confirmed that the curvature of the channel bend plays a fundamental role, i.e., scour features significantly differed from those occurring in straight channels. Likewise, the inclination of the sill and its shape affect the scour morphology. The presence of the sill and the curvature of the channel caused an asymmetric distribution of the flow in the radial direction, possibly resulting in a shift of the scour hole toward the center. The analysis of experimental data allowed us to provide practitioners with a useful formula to predict the maximum scour depth. Finally, interesting insights on scour dynamics and features at equilibrium are also presented.
Air-Water Flow Patterns and Shockwave Formation in Low-Level Outlets
Pagliara, Simone; Hohermuth, Benjamin; Boes, Robert (2023)
Journal of Hydraulic Engineering
Reservoir dams play a significant role in society and the economy. Low-level outlets (LLOs) are key safety devices providing reservoir drawdown for maintenance and emergency purposes, sediment flushing, and release of environmental flow. High velocities and turbulence levels of the free-surface flow lead to air entrainment and air transport along the LLO tunnel, resulting in subatmospheric air pressures. In addition, shockwaves formed downstream of the gate may lead to a complete filling of the tunnel cross section, possibly resulting in slug flow and flow pulsations, which should be avoided for operational safety. In this study, physical model tests were performed to investigate the effects of gate opening and hydraulic head on shockwave patterns. Especially for large contraction Froude numbers, the shockwaves were strongly aerated, resulting in a complex air-water flow pattern. The results provide insights into the formation and propagation of shockwaves, contributing to an improved design of LLO tunnels.
Intrusive effects of dual-tip conductivity probes on bubble measurements in a wide velocity range
Pagliara, Simone; Felder, Stefan; Boes, Robert Michael; et al. (2024)
International Journal of Multiphase Flow
High-velocity air-water flows in hydraulic structures, such as spillways and low-level outlets, are characterised by high turbulence levels and strong self-aeration. In air-water flows, the void fraction varies from values close to zero at the invert up to near unity in the upper spray region. Because of the strong aeration, non-intrusive optical measurement techniques can only be applied to a limited extent, and intrusive phase-detection probes are widely used to estimate air-water flow properties, including void fraction, interfacial velocity, and chord sizes. However, these probes are often used without independent validation. Herein, this study systematically investigated the uncertainties of phase-detection probe measurements of individual bubbles traveling at a wide range of velocities (up to 7.5 m/s) in a vertically upward bubbly pipe flow. Velocities and chord times of air bubbles were simultaneously measured with an intrusive dual-tip conductivity probe and stereo-view high-speed videos, and a comparative analysis identified various effects of bubble-probe interactions on the measurement accuracy of the bubble velocities. The bubble deceleration due to these bubble-probe interactions were quantified. For standard interactions (i.e., bubbles undergoing no significant deformation and slowing down), the velocity estimates compared well with a theoretical model (errors less than 2 %), while larger errors were found for non-standard interactions such as those characterised by crawling, drifting, and waking mechanisms. In addition, a novel correction scheme for chord times was proposed, improving the accuracy of chord length, bubble size and void fraction estimations in air-water flows.
Effects of Wall Roughness on Air-water Flow Properties of Low-level Outlets
Pagliara, Simone; Hohermuth, Benjamin; Felder, Stefan; et al. (2023)
Proceedings of the 40th IAHR World Congress
Reservoir dams serve many purposes, including hydropower production, climate change mitigation, and flood control. Low-level outlets (LLOs) are key safety structures of high-head dams. Their main purpose is to control the water level in the reservoir during flood events or maintenance works, and to support a rapid drawdown of the reservoir in case of emergency situations. Alternative purposes include controlling the first impounding of the reservoir, sediment flushing, turbidity current venting, and releasing of environmental flow to preserve downstream river health. In the free-surface tunnel, flow velocities can reach values of several dozen meters per second, leading to significant air transport and sub-atmospheric pressures which may induce or aggravate problems with cavitation and gate vibration. Sufficient flow aeration is crucial to mitigate these issues and to achieve a safe and reliable operation of LLOs. Despite recent new insights on the influence of hydraulic and geometric tunnel parameters on air-water flow properties in LLOs, the effect of wall roughness on their performances is still unclear. Considering that wall roughness and Reynolds number are often the key differences between scale models and prototype structures, novel physical model tests were performed to investigate the influence of tunnel wall roughness on key air-water flow properties including void fraction and interfacial velocity. Different combinations of gate opening and energy head at the gate were tested, corresponding to Froude and Reynolds numbers at the vena contracta up to 46 and 8·105, respectively. Two wall roughness configurations representing unlined rock and finished concrete were tested, and measurements were taken by means of a dual-tip phase-detection conductivity probe. Results indicate that the tunnel roughness has a significant effect on the air-water flow properties, leading to larger flow depths associated with higher void fractions and smaller interfacial velocities, while the turbulence levels increased. This study contributes to a safer design of LLO tunnels.
Scour features at wood bundles
Pagliara, Simone; Roy, Deep; Palermo, Michele (2021)
Water
Structures like blunt-nosed chevrons, log deflectors and double-winged log frames help in modifying the flow regime in the channel by concentrating the flow and increasing navigability. Moreover, they create scour pools in the downstream stilling basin, which can be used either as fish refuge or as an in-stream storage site for previously dredged material. In this respect, the use of wood debris in the channel in the form of wood bundles has gained attention for the ability of these structures to integrate into the surrounding fluvial habitat and to divert the flow partially towards the central part of the channel when placed in curves. Considering the absence of studies dealing with wood bundles as a restoration structure, the aim of this paper is to analyse the scour mechanism and equilibrium scour morphology of wood bundles in straight and curved channels. In doing so, a wide range of hydraulic conditions, structure positions and configurations were tested. Thereafter, dimensional analysis was carried out to derive useful empirical relationships to predict the maximum scour depth and length as well as the maximum dune height based on a novel, equivalent Froude number, which accounts for the effects of channel curvature and structure position. Moreover, the various resulting scour morphology types were classified, and conditions of their existence were determined depending on the abovementioned Froude number and other key hydraulic parameters.
Effects of wall roughness on low-level outlet performance
Pagliara, Simone; Hohermuth, Benjamin; Felder, Stefan; et al. (2023)
Role of Dams and Reservoirs in a Successful Energy Transition
Reservoir dams play a key role in modern society, water resources management and economy. Low-level outlets (LLOs) represent important safety structures for regulating the water level in the reservoir, and for its fast drawdown in case of scheduled maintenance or emergency situations. The flow in LLO tunnels is characterized by high velocities and turbulence levels, leading to air entrainment and transport. This results in sub-atmospheric air pressures, which may induce and aggravate serious issues such as gate vibration and cavitation. An adequate flow aeration via an air vent can mitigate these problems and is key to good performance. While many studies focused on the effects of hydraulic parameters, tunnel geometry and air vent design on the air demand of LLOs, the influence of the tunnel wall roughness is still unclear. To this end, physical model tests were carried out to investigate the effects of invert, soffit, and sidewall roughness on the LLO performance, for various combinations of gate opening, energy head at the gate and air vent properties. The roughness modelled in this study represents unlined rock, and it was implemented by attaching expanded aluminum plates to the inner sides of the outlet tunnel. Air velocities in the air vent were measured to estimate the air demand, and pressures along the tunnel were recorded to assess cavitation potential. For rough wall conditions, both the air demand and the cavitation risk were found to increase compared to the smooth tunnel conditions (i.e., acrylic-made invert, walls, and soffit in the model). In conclusion, the study represents a preliminary analysis of the effects of LLO tunnel roughness on air demand and cavitation occurrence, and future research is needed to enable a more quantitative assessment of the differences in air demand between model and real-world prototypes.
Control of Surface Plastic Transport in Natural Streams
Roy, Deep; Palermo, Michele; Pagliara, Simone (2024)
Journal of Hydraulic Engineering
In the aftermath of the worldwide severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, the disposal of plastic and nonwoven fabric materials originating from personal protective equipment (PPE) into freshwater bodies like lakes and rivers has significantly increased. Surface plastic transport and accumulation have become a relevant source of pollution that adversely affects the quality of water and fluvial ecosystems. Although attempts have been made in the past to study the flow characteristics of plastic at the river surface, an in-depth study of structural configurations that can act as potential plastic traps, facilitating reduction of pollution due to plastic transport, is necessary. This paper investigated the hydrodynamics of surface plastic transport in the presence of several control structures. In addition, useful empirical equations were derived to predict the kinematic and trapping efficiency of the mentioned structures, valid for both straight and curved channels under a variety of hydraulic and geometric conditions. It was found that the Froude number and position of the structure play a dominant role in influencing surface plastic transport mechanism and the overall efficiency of structures in limiting plastic transported downstream.
Preliminary Analysis on the Effect of Tunnel Profile Transitions on Air-demand and Flow Patterns of Low-level Outlets
Pagliara, Simone; Felder, Stefan; Hohermuth, Benjamin; et al. (2024)
Proceedings of the 10th International Symposium on Hydraulic Structures (ISHS 2024)
Reservoir dams are decisive for energy supply and water resources management, thus playing a crucial role in modern society and economy. Low-level outlets (LLOs) are important safety structures of dams, aiming at regulating the water level in the reservoir, and at allowing a fast drawdown in case of maintenance or emergency situations. A typical LLO consists of a pressurized inflow controlled by a gate and a free-surface outlet tunnel. The transition from pressurized to supercritical free-surface flow is responsible for the generation of a high-speed water jet, resulting in significant turbulence levels, air entrainment, and air transport along the tunnel. Sub-atmospheric pressures typically develop downstream of the gate, potentially triggering significant problems such as gate vibration and cavitation. A sufficient flow aeration is crucial to mitigate these issues, and an appropriate air supply system should be designed downstream of the gate. Several empirical design equations have been developed in literature to predict the relative air demand (i.e., the ratio of air discharge through the vent and water discharge in the outlet tunnel) of LLOs, accounting for the effects of flow patterns, air vent loss coefficient, tunnel slope, length, and roughness. Nevertheless, the comparison against prototype data showed a significantly larger air demand compared to the model-based equations mainly due to geometrical differences, resulting in non-negligible effects of tunnel roughness, profile transitions, and scale. In this regard, there has been no systematic study investigating the effect of tunnel profile transition on air demand and flow patterns. To narrow this gap, large-scale physical model tests were carried out to investigate the effects of an abrupt and a gradual linear tunnel profile transition on the LLO performance, for various combinations of gate opening, energy head at the gate and air vent properties. The two tunnel profile transitions resemble those commonly found in real-world prototypes. Preliminary observations showed that the profile transitions significantly affect the flow patterns compared to tunnels featuring no transitions, resulting in more complex and larger shockwave formation downstream of the gate. This also leads to an overall increase in the air demand for similar inflow conditions. This study provides preliminary recommendations for a safe design of LLO tunnels featuring gradual and abrupt profile transitions, contributing to a safer design of such structures.

Publications 1 - 10 of 17

Simone Pagliara

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