Hydraulic Transients Research Articles

Effects of tidal bore on hydraulic transients in low-head pressurized water conveyance systems

Effects of tidal bore on hydraulic transients in low-head pressurized water conveyance systems

Hydraulic impact of pressure transients from water conveyance tunnel on the complex hydrogeological system: A case study HPP Pirot, Serbia

Hydraulic tunnels, integral components of hydropower plant (HPP) systems, traversing diverse rock masses, pose challenges for long-term operation. The study’s main goal was to investigate how hydraulic transients originating from the headrace tunnel transfer through the concrete lining and manifest in surrounding aquifer systems. In this experimental study at the water pressure tunnel of HPP Pirot (Serbia), a novel monitoring approach was employed. The internal piezometers with highly sensitive probes are distributed strategically along the tunnel in different geological environments. This approach involved monitoring of water pressure in the surrounding rock masses and observing the impact of hydraulic transients generated by HPP operation. A comprehensive analysis of monitoring data, incorporating ordinal and partial correlations and considering geological features, provides a profound understanding of groundwater dynamics, pressure transient phenomena, and hydrogeological characterization during HPP operation. The study highlights the complex and spatially diverse hydrogeological environment, emphasizing the varying reactivity of pore pressure during HPP operation, particularly concerning Water Mass Oscillations (WMO). Reactive piezometers near the surge tank demonstrate significant pressure variations, while those located further away display synchronous pressure changes with reduced amplitudes. Schematic hydrogeological models have been created based on the hydraulic impacts of HPPs in different geological environments along the tunnel route. The water pressure response enabled aquifer characterization of (1) a thin-layered, low-fissured aquifer closely related to the reservoir, with low influence on WMO transients; (2) a low-fissured, compartment aquifer or non-aquifer with minimal to no influence on WMO transients; (3) a well-structured karst aquifer system influenced by WMO transients; (4) a fault-controlled zone of deep hypogene karst aquifer discharge highly influenced by WMO transients; and (5) an aquifer with a dominant development of the karst conduit system highly influenced by WMO transients. The study highlights the significance of monitoring water pressure within the rock mass as a fundamental element in analyzing the interaction between water pressure tunnels and the hydrogeological environment. Applying the presented instrumentation and methodology facilitates effective monitoring in research areas where pressure tunnels are constructed.

Influence of gate cutoff effect on flow mode conversion and energy dissipation during power-off of prototype tubular pump system

Understanding the cutoff effect of gates is essential for enhancing the overall quality of the pump system's power-off process, minimizing energy losses, and reducing potential risks associated with hydraulic transients. In this study, both numerical simulations and experimental investigations were conducted on the power-off process of a tubular pump system, considering scenarios with and without gate functionality. The simulations utilized a dynamic mesh method to model gate movement, incorporated the torque balance equation to determine the real-time impeller speed, and applied the 3D-VOF method for free surface modeling in reservoirs. Power-off experiments were performed on a model pump system and a prototype pump system to validate the numerical simulation results. To elucidate the mechanism of the gate's cutoff effect, flow modes during the power-off process were categorized based on the four-quadrant static test results of the pump, revealing the deviations between transient and static characteristics. By comparing the transient flow structures of the pump system under different gate operating states, specific energy dissipation behaviors during gate cutoff were analyzed. The research findings enhance the understanding of hydraulic transients, which is essential for developing more sustainable and resilient energy systems.

Online state estimation in water distribution systems via Extended Kalman Filtering

Operators of water distribution systems (WDSs) need continuous and timely information on pressures and flows to ensure smooth operation and respond quickly to unexpected events. While hydraulic models provide reasonable estimates of pressures and flows in WDSs, updating model predictions with real-time sensor data provides clearer insights into true system behavior and enables more effective real-time response. Despite the growing prevalence of distributed sensing within WDSs, standard hydraulic modeling software like EPANET do not support synchronous data assimilation. This study presents a new method for state estimation in WDSs that combines a fully physically-based model of WDS hydraulics with an Extended Kalman Filter (EKF) to estimate system flows and heads based on sparse sensor measurements. To perform state estimation via EKF, a state-space model of the hydraulic system is first formulated based on the 1-D Saint-Venant equations of conservation of mass and momentum. Results demonstrate that the proposed model closely matches steady-state extended-period models simulated using EPANET. Next, through a holdout analysis it is found that fusing sensor data with EKF produces flow and head estimates that closely match ground truth flows and heads at unmonitored locations, indicating that state estimation successfully infers internal hydraulic states from sparse sensor measurements. These findings pave the way towards real-time operational models of WDSs that will enable online detection and mitigation of hazards like pipe leaks, main bursts, and hydraulic transients.

Generalized characterization of pipeline systems with air chamber through development of the dimensionless impedance response

ABSTRACT An air cushion chamber is a feasible and efficient hydraulic device to control water hammer for pressurised pipeline systems. The introduction and evolution and hydraulic transient depend on distinct features of pipeline systems such as length, diameter and the property of pipeline extension as physical properties; flowrates, pressure, boundary conditions as hydraulic conditions; and interaction with surge protection devices (air chamber) as hydraulic conditions. Considering all factors simultaneously can be incredibly difficult, even for a simple air chamber pipeline valve layout. This study introduces the dimensionless transfer function and expression for air chambers in dimensionless frequency domain in order to effectively address the water hammer generation and its counteracting processes. To comprehensively characterize hydraulic transients for pipeline systems equipped with air chambers, two representative dimensionless parameters were used. Along the pipeline system, it is possible to develop a frequency-independent expression for hydraulic impedance. A comparison between the developed method and other existing methods (e.g. characteristic method and impulse response method) revealed excellent agreement. Application of the dimensionless parameters to systems with different dimensions and hydraulic conditions shows that the proposed dimensionless parameters can address substantial ranges of real systems.

A study of valve-induced water hammer in a woven-jacket fire hose

ABSTRACT The dynamic response of a woven fire hose during valve-induced water hammer events is investigated through a combination of experimental and numerical studies. Unlike conventional polymeric pipes, fire hoses made of synthetic fibres exhibit unique characteristics, transitioning from pliancy to increased rigidity as the pressure within the hose rises. This study explores the transient behaviour of woven fire hoses under variable initial conditions. Experimental studies reveal a direct correlation between the initial piezometric head and the fire hose’s transient response. Numerical simulations employ the viscoelastic Kelvin–Voigt model, proving its suitability for accurately simulating valve-induced hydraulic transients in woven fire hoses. Notably, even a single Kelvin–Voigt element exhibits a relatively good fit with experimental data, accurately reproducing pressure peaks, while the inclusion of two elements enhances the model’s capability, achieving the near-perfect reproduction of pressure oscillations.

Hydraulic transient calculation by wave tracking method for pumped storage power plant with four units in a diversion system

Abstract Hydraulic transient calculations are a key issue related to the operational safety of pumped storage power plants. Based on the new calculation method, wave tracking method, this paper establishes a calculation model for the hydraulic transient of pumped storage power plant, verifies the accuracy of the calculation model through hydraulic model experiments, and calculates the transient process of Guangdong Qingyuan pumped storage power plant. The results show that the calculation error is reduced by considering the difference of wave velocity of different branch pipes by wave tracking method. The wave tracking method is convenient to establish a calculation model of pumped storage power plant with four units in a diversion system, which is suitable for the load shedding transient regime of the turbine mode and the pump outage condition, and the accuracy is good. Wave parameters visually show the connection between flow rate, pressure changes within the water transmission system, and surge fluctuations in the regulator well throughout the hydraulic transition.

Sensitivity analysis of influencing factors in large oscillation hydraulic transient process of pumped storage power station

Abstract The calculation of large oscillation transition process is of great significance for pumped storage power station, which is beneficial for ensuring the safe of the power station and extending the lifespan of the unit. Due to the presence of inertia in water and rotating components of the unit, as well as energy imbalance in the system, hydraulic transients will cause drastic changes in water pressure in the waterway system and unit speed, resulting in a sharp increase or decrease in pressure and a sharp change in unit speed, endangering the operational safety of the power plant and affecting the lifespan of the unit. It is necessary to optimize the layout of water conveyance system, basic parameters of units, and the closing law of guide vanes through calculation and analysis of large oscillation transition processes. Relying on a pumped storage power station in Guizhou, this paper analysis the sensitivity of the factors affecting the calculation results of the large oscillation transition process, such as runner characteristics, guide vane closing law, moment of inertia GD2, surge chamber diameter and restricted orifice size, to provide reference for similar projects.

Effect of guide vane closing speed deviation on transition process in pumped storage power plant

Abstract The guide vane closing law is a crucial role in ensuring the hydraulic transients of pumped storage power plant. It is also essential for ensuring the safe operation of pumped storage power plant after long-term operation. Variations in the closing speed between simulated guide vane closing laws and on-site closing laws have been observed. This study first verifies the accuracy of the simulation model through load rejection tests conducted on two units. It then simulates the deviation in guide vane closing speed for these units. The deviation in guide vane closing speed does not impact the regulatory requirements for a single unit. However, variations in the closing speed between simulated guide vane closing laws and on-site closing laws have been observed. This study first verifies the accuracy of the simulation model through load rejection tests conducted on two units. It then simulates the deviation in guide vane closing speed for these units and proposes a reference range. The deviation in guide vane closing speed does not impact the regulatory requirements for a single unit. However, for two units in one pipe, opposite deviations in guide vane closing speed can result in key parameters failing to meet regulatory requirements.

Predicting pump-turbine characteristic curves by theoretical models based on runner geometry parameters

The characteristic curve of a pump-turbine is the essential data for calculating the hydraulic transient processes of a pumped storage power station. However, this curve is often unavailable during the preliminary design stage of pumped storage power stations. The shape of the characteristic curve directly influences the transient guarantee parameters. To date, adjusting the runner geometry to control the characteristic curve's shape for improving hydraulic transients remains a challenging issue. This paper proposes a model for predicting the characteristic curve that correlates its shape with the runner's geometric parameters. Considering the bidirectional flow in pump-turbines, two sets of governing equations are derived separately for the centripetal and centrifugal flow conditions. The governing equations for the unit discharge curve and the unit torque curve are constructed based on the energy equation and torque equation, respectively. Each term in these equations is subsequently organized into the expressions involving the runner's geometric parameters and unit parameters. To make the equations solvable, several sets of feature points are introduced. Based on the approach to obtain the feature points, an experiment/CFD (Computational Fluid Dynamics)-based prediction method and a statistics-based prediction method are proposed. Verifications using manufacturer-measured curves show that the experiment/CFD-based method is well-suited for model test acceleration and characteristic curve repair due to its higher prediction accuracy and availability, while the statistics-based method is more suitable for borrowing similar curve data during the power plant's preliminary design phase or rapidly predicting the corresponding characteristic curves during runner design. This work establishes a theoretical basis for improving hydraulic transient guarantee parameters by runner design optimization.

Water hammer mitigation by internal rubber hose

The aim of this research was to experimentally analyse the possibility of using a rubber hose placed inside a pipeline to mitigate the water hammer phenomenon. The experiments were conducted using a steel pipeline with an inner diameter of 53 mm and an EPDM rubber hose with a diameter of 6 mm. Hydraulic transients were induced by a rapid closure of the valve located at the downstream end of the pipeline system. In order to analyse the influence of steady-state flow conditions on the maximum pressure increase, measurements were carried out for different values of initial pressure and discharge. The experimental results indicate that placing a rubber hose inside a pipeline can substantially attenuate valve-induced pressure oscillations. It was observed that the initial pressure has a significant influence on the capacity of the rubber hose to dampen the water hammer phenomenon. Comparative numerical calculations were performed using the Brunone–Vitkovský instant acceleration-based model of unsteady friction. It was demonstrated that this approach does not allow satisfactory reproduction of the observed pressure oscillations due to the viscoelastic properties of the EPDM hose used in the tests.

Investigation Of The Influence Of The Turbine Wicket Gates Closure Law Pattern On The Water Hammer Effect During Turbine Off-Design Operation

Hydraulic transients are accelerated by the wicket gate closing in hydroelectric power plants. When the wicket gate is closed, there is a sudden change in velocity due to the closure. Therefore, a study has been carried out here, wherein water hammers on different hydropower components use optimum closure laws: Fast closure laws, slow closure laws, and instant load rejection. Hammer V10i software was used to investigate the phenomenon of pressure transient. The results show that the maximum transient pressure is strongly influenced by a very short closing time and was increased to 41.24% from the slow to the fast closure.
 Furthermore, the results from instant load rejections reveal that the transient pressure will be less than the fast and slow closure. So, the closing law selection can positively influence the entire hydropower plant system. Furthermore, the results show that there was a decrease in pressure near the turbine during the different load rejections, Fast closure, slow closure, and instant load rejection, where 57.7%, 15%, and 0.46%, respectively, and the decrease in turbine rotation speed were as 5.1%, 60%, and 24% respectively. Moreover, results reveal that maximum and minimum flow variation reached -29.75% and 41.2% during the fast closure.
 

Brazilian savannah tree as bio-inspiration for hydraulic transient control in a penstock of a small hydropower plant

This study proposes an innovation, which is to use a non-circular and bio-inspired forced conduit (a new penstock with a cross section inspired by a tree trunk), to control the effects of hydraulic transients in Brazilian small hydropower plants (SHPs). The aim is to demonstrate that natural structures, adapted to periodic environmental disturbances, are better at hydraulic transient control than traditional conduits. The proposed methodology includes the following steps: (1) problem identification; (2) potential biological model identification; (3) development of alternatives; (4) implementation and testing; and (5) solution selection. This research was conducted at the São Tadeu I SHP, in the city of Santo Antônio de Leverger/MT, Brazil. The following tree biological models from the Brazilian savannah (Cerrado) were used: Handroanthus capitatus and Strychnos pseudoquina. The proposed innovation improves the conduit of the traditional circular section and the relief valve solution of the criteria studied. The reason for this improvement was the reduction of wave speed in the non-circular section (from 1126 to 583 m s−1).

Simplified approach for sizing surge tank in long-distance pipeline systems

The cross-sectional area of a surge tank (CAST) is a key factor for protecting pipelines from harm by hydraulic transients. However, for long-distance pipeline systems (LDPS), the water level fluctuations in the surge tank and valve closure water hammer normally share a coupling relationship. Traditionally, this coupling relationship renders difficulty in determining the CAST. This study focused on the influence of water level fluctuation and water hammer, and proposed a simplified approach for sizing surge tanks. First, a water hammer formula that considers the coupling effect was derived. Subsequently, formulae for sizing the CAST were deduced. Finally, a case study of an actual LDPS was conducted to verify the accuracy of the presented formulae. In addition, the calculation errors caused by the theoretical assumptions are discussed. The results indicate that the theoretical calculation values and time-domain simulation results match well, thereby demonstrating the great convenience of designing surge tanks.

Transient-based multiple branch detection in reservoir pipeline valve systems

Efficient management of pipeline assets is crucial for a reliable urban water supply. Unknown side branches in pipeline systems can hinder the prediction of hydraulic transients, owing to unexpected pressure responses. Herein, we developed a method for detecting multiple side branches in a simple reservoir pipeline valve system. A polynomial-based transient characterization scheme was proposed to address nonlinear valve manoeuvres, which substantially improved the transient simulations over conventional orifice-based approximations. A procedure for pressure signal manipulation via the superimposition of pressure signals with and without branches and isolation of the interference between various branched elements, which distorted the pressure response of multiple branches, was introduced. The model performance was evaluated by comparing the interference-isolated signals obtained from the conventional method, proposed scheme, and experimental datasets. Effective phase matching of the pressure responses obtained via the proposed scheme and experimental data indicated the potential of the former for detecting multiple branches.

Entendendo o risco de descoloração como consequência de transientes hidráulicos

Abstract This paper presents an analysis of the challenges associated with discoloration risk management and the impact of hydraulic transients on water quality within distribution systems. Focusing on the Metropolitan Region of Curitiba, Paraná, Brazil, the study employs a comprehensive methodology that combines the Characteristic Method for simulating hydraulic transients and real-time monitoring of water quality parameters, such as turbidity and chlorine levels. A framework for managing discoloration risk is proposed, highlighting strategies for identifying potential causes, assessing risk severity, developing prevention and mitigation strategies, and implementing continuous improvement processes. The experimental section details the impact of hydraulic transient events on water quality, with significant findings indicating a direct correlation between flow dynamics and water quality degradation, particularly in terms of increased turbidity and decreased chlorine levels during pump deactivation. The study contributes valuable insights into effective water distribution system management, emphasizing the importance of advanced monitoring and risk management techniques to maintain high-quality water standards.

ПЕРСПЕКТИВИ ВИКОРИСТАННЯ ПРОГРАМНОГО ЗАБЕЗПЕЧЕННЯ ЧИСЕЛЬНОГО МОДЕЛЮВАННЯ ДЛЯ АНАЛІЗУ ТА ДОСЛІДЖЕННЯ ГІДРОУДАРІВ

The Pipe Flow Module simulates fluid dynamics, heat and mass transfer, hydraulic transients, and acoustics in pipe networks. It integrates seamlessly with other modules in the COMSOL® Product Suite, enabling efficient modeling of piping's impact on larger

Hydraulic Transient Impact on Surrounding Rock Mass of Unlined Pressure Tunnels

The frequent pressure pulsations due to hydraulic transients in hydropower plants induce cyclic loading on the rock mass that may contribute to increased instances of block falls and increased risk of tunnel collapse over the power plant lifetime. This study focuses on understanding the effect of frequent start and stop sequences of hydropower in unlined pressure tunnels. For this purpose, data from a pore water pressure monitoring system is utilized, which was installed at the downstream end of the headrace tunnel at the 50 MW Roskrepp hydropower plant in southern Norway. The objective of this study is to analyze the recorded data and quantify the impact of the hydraulic transient on the surrounding rock mass in the unlined pressure tunnel. The monitoring of pressure data over several years clearly shows that frequent load changes could cause a considerable effect on the rock mass and constituent joint system. A delayed response of the pressure in boreholes in the rock mass compared with inside the tunnel is seen in all start and stop sequences and is considered to be the main reason for instability caused by transients. The response of pore pressure in boreholes is greatly influenced by the characteristics of joints. The results show that the start sequence and shorter shutdown duration exert a greater impact on rock mass as compared to the stop sequence and longer shutdown duration. Therefore, it is recommended to increase the shutdown duration so that the impact can be minimized to increase the tunnel lifetime. This study recommends implementing a more conservative design approach in tunnels with weak rock masses in projects that involve frequent load changes.

Experimental and numerical Investigation of entrapped air presence and expulsions in irregular pipelines on hydraulic transients

In the present study, the transient event of rapid opening of upstream valve in undulated water pipeline with entrapped air pockets was investigated both experimentally and numerically. Pressure peaks and oscillation patterns were traced with the variation of air pocket length, blocking column length and water filling column. A transient two-dimensional CFD simulation model was introduced and validated by laboratory experiments. The proposed CFD model was conducted using ANSYS fluent based on Reynolds-averaged Navier–Stokes (RANS) equations and the volume of fluid (VOF) method. A user-defined functions (UDF) for both water compressibility effect and opening valve estimated pattern were adopted to verify the experimental results. For further understanding of transient response air expulsion through air vents of various orifices diameters were experimentally investigated. Image processing technique by using photoshop were utilized to clarify Stages of air expulsions, air water interaction and orifice flow regime. The obtained results showed that pressure peaks and oscillations depend strongly on orifice size where small orifice caused an intermitted flow choked by water column in contrast to large orifice where water hammer was dominated. An experimental facility was constructed at Alexandria university hydraulics laboratory to fulfil the research objectives. Air presence challenges in hydraulic systems are extensively applied for water and fuel supply lines, firefighting, and drainage systems in airports ground facilities.

Unified Approach for Damping Rate of Transient Laminar Flow: Experiments, Computational Fluid Dynamics, and One-Dimensional, and Global Models

Abstract Pipe networks exhibit complex geometries and are equipped with electromechanical devices capable of generating hydraulic transients. Most of these devices are remotely controlled and managed through an integrated system that prioritizes network demands. This implies that potential hazardous pressure peaks, that may occur during each operation, may need to be taken into account. Consequently, when multiple operations take place in a short time interval, transient pressure waves, generated in different parts of the network and traveling back and forward, overlap and can be larger than the design maximum pressure. To address this concern, it is essential to evaluate the pressure-damping rate of critical maneuvers and to identify a “safe” time interval between maneuvers to prevent the risk of inappropriate pressure waves overlapping. With the aim of analyzing the damping rate of closure maneuvers, both numerical and laboratory experiments have been executed for a laminar flow in a reservoir-pipe-valve system. In this context, a three-dimensional computational fluid dynamics, a one-dimensional and global model, the latter based on a sinusoidal function, have been used. Guidelines are then presented for identifying the safe time interval between maneuvers.