Abstract Cavitation presents a significant challenge in the operation and longevity of hydraulic machinery. Studying single cavitation bubble can provide fundamental insights into phenomenon. One simple popular method to generate such bubbles is through low-voltage discharge between two contacting electrodes create spark that locally vaporizes water. This study investigates repeatability this generating consistent bubbles. The electrode length one parameter influences size. However, excess...

Because of the introduction significant amounts electricity from intermittent energy, such as solar and wind, on power grids, hydraulic turbines undergo more transient operation with varying rotation speeds. Start stop sequences are known to induce mechanical stress in runner, decreasing its lifespan. Complex fluid–structure interactions responsible for those high-stress levels, but precise mechanisms still elusive, even if many experimental numerical studies were devoted subject. One...

Hydraulic turbines are more frequently used for power regulation and thus spend time providing spinning reserve electrical grids. Spinning requires the turbine to operate at its synchronous rotation speed, ready be linked grid in what is termed speed-no-load (SNL) condition. The turbine's runner flow SNL characterized by low discharge high swirl leading low-frequency amplitude pressure fluctuations potentially blade damage maintenance downtime. For low-head hydraulic operating SNL, large...

Within the framework of an international research consortium on low-head hydraulic turbine flow dynamics, predictive behavior Reynolds Averaged Navier-Stokes (RANS) simulations efficiency (η) hill chart a bulb is investigated. The paper presents impacts blade tip gap and hub gaps performance predictions.

Transient conditions such as load rejection will often lead to high amplitude pressure fluctuations that affect a turbine residual-life. If Computational Fluid Dynamic offers promising tool study the flow dynamic under transient regime, focused validation data on runner are still lacking assess accuracy of different simulation strategies. Hence within framework AxialT project International Consortium Hydraulic Machines, exploratory measurements field blades propeller model were performed in...

Hydraulic turbines sometimes exhibit a sharp efficiency drop around the best point. The is known to originate from large flow separations in their draft tubes, limiting ability recover part of residual kinetic energy exiting runner. While conditions leading onset these are not yet understood, potentially unstable vorticity distribution at runner exit led hypothesis that those result an interaction between center tube and boundary layer walls. To study this hypothesis, turbulent inside bulb...

The draft tube of reaction hydraulic turbines is subject to numerous investigations since it accounts for a significant portion the energy recovery. But even with up-to-date computational fluid dynamics methodologies, simulating flow remains highly challenging diverging swirling that may undergo separations and become dominated by unsteady secondary flows. Within framework collaborative research project on propeller turbine model, at inlet region was studied using 2D-laser Doppler...

A good evaluation of the unsteady pressure field on hydraulic turbine blades is critical in evaluating lifespan and its maintenance schedule. Low-head turbines such as Kaplan Propeller, using a relatively low number supported only at hub, may also undergo significant deflections blade tips which will lead to higher amplitude vibration compared Francis turbines. Furthermore, precise distribution low-head still challenge for computational fluid dynamics (CFD). Within framework an international...

Within the framework of BulbT project, simulations were performed to understand origin a measured hysteresis on efficiency hill chart bulb turbine model. This is associated with sharp drop located at slightly higher discharge than best operating condition. It appears as variation in performance whether an condition reached from lower or discharge. was reproduced numerically using Reynolds Averaged Navier Stokes (RANS) simulations. The paper presents experimental results, numerical...

The increasingly common utilization of hydraulic turbines in off design operating conditions recent years have affected their lifetime due to damaging fluid-structure interactions. To decrease the downtime associated more frequent maintenance these turbines, a thorough understanding flow phenomena is required. This may eventually lead development mitigation strategies. However, measuring velocity at entrance rotor Francis difficult because confined spaces and limited optical access. paper...

Recent researches indicate that the useful life of a turbine can be affected by transient events. This study aims to define and validate strategies for simulation flow within propeller model in runaway condition. Using unsteady pressure measurements on two runner blades validation, different are compared their results analysed order quantify precision. paper will focus justifying choice simulations analysis preliminary results.

No-load operation is among the most damaging operating conditions. Since no energy extracted by turbine during this operation, fluid dissipated highly energetic and turbulent flow phenomena causing high pressure strain fluctuations on components. These flows are complex and, until now, poorly understood. This paper presents preliminary three-dimensional simulations of no-load within a head Francis at model scale using Computational Fluid Dynamics SAS-SST turbulence model. The numerical...

Abstract For Francis turbines, speed-no-load (SNL) represents one of the most detrimental operating conditions, marked by significant pressure and strain fluctuations on runner. Mitigating these necessitates a comprehensive understanding characterization flow phenomena responsible for their generation. This paper presents an experimental investigation at inlet turbine runner model in condition using high-speed stereoscopic endoscopic particle image velocimetry (PIV). The measurements are...

The BulbT project involved several investigations of flow phenomena in different parts a model bulb turbine installed on the test rig Laval University Laboratory. aim is to create comprehensive data base order increase knowledge this type turbines and validate or improve numerical simulation strategies. This validation being based kinematic comparison between experimental data, had overcome challenges facilitate use for that purpose. Many parameters were checked, such as bench repeatability,...

Steady state and non-linear harmonic (NLH) flow simulations were performed within the framework of Francis-99 project in order to assess capacity NLH method capture main pressure fluctuations associated with rotor-stator interactions between distributor runner turbine. This paper focusses on methodology developed obtain solutions presents preliminary results from using solver NUMECA FineTURBO intermediate grid level meshes. Comparisons first experimental data reveal good agreement concerning...

Abstract For hydraulic turbines, no-load (NL) is considered a homogeneous family of operating conditions, although the literature exposes wide variety flow structures depending on many factors. A better understanding developed during NL operation necessary, since they generate pressure fluctuations in turbine causing significant fatigue damage and reducing life expectancy machines. Hydraulic turbines at model scale show that behavioral trends can be identified for conditions. This paper...

Abstract Emergence of new renewable energies, such as solar or wind power, has introduced intermittency on the grid. Hydraulic turbines, initially designed to perform close their best efficiency point, are more and at off-design operating conditions, no-load regimes, when runner rotates without energy extraction. These regimes characterized by complex flow phenomena inducing fluctuations blade loading resulting in a reduced lifetime runner. Understanding origins pressure conditions is...

Hydraulic turbines with high efficiency over a wide range of operating conditions offer much sought-after flexibility to electricity producers. However, some low-head exhibit sharp losses close their peak discharge that are linked draft tube flow separations whose causes remain misunderstood. This paper presents the latest results obtained in scope BulbT project focused on dynamics related drop. The main objectives document transient characteristics hub-wake region and investigate...

The hydro renewable energy provides a reliable power source; it does not pollute the air or land but affects aquatic habitat due to low dissolved oxygen (DO) level in water discharged from turbines. Hydro-turbines intake generally withdraws bottom layer of reservoirs with DO level. In different methods used for improving downstream hydropower plants volume is considered be main parameter injection. energetic consumption affected, terms loss turbine efficiency authors propose study show...

It is a well-known fact and much studied problematic that the performance of low-head hydraulic turbines highly dependent on runner–draft tube coupling. Around optimal operating conditions, efficiency turbine follows closely draft in turn depends velocity field exiting runner. Hence, order to predict correctly using numerical simulations, flow inside runner must be simulated accurately. Using results from unique detailed particle image velocimetry (PIV) laser Doppler (LDV) measurements...