Xavier Escaler

Polytechnic University of Catalonia | UPC · Department of Fluid Mechanics (MF)

To study the effects of fluid compressibility on the dynamics of a cavitating vortex street flow in a regime where the vortex shedding frequency increases as a result of the cavitation increase, the cavitating wake behind a wedge was simulated employing both incompressible and compressible solvers. To do this, a compressible cavitation model was im...

The cavitating wake behind a wedge has been simulated employing both incompressible and compressible solvers with the purpose of comparing their performance. To develop the compressible solver, the ZGB cavitation model for incompressible flows has been modified to consider the compressibility effects. First, the equations of state for the vapor and...

In hydraulic turbines, several flow instabilities can take place inside the draft tube cone during off-design and transient operating conditions such as the rotating vortex rope which can severely damage the structure if sustained in time. In the frame of the AFC4Hydro H2020 research project, an extensive measurement campaign has been carried out t...

Under off-design operating conditions, the flow through hydraulic turbines presents fluidodynamic disturbances that can excite a natural frequency and provoke a resonance. Determining with precision the modal properties of the runner is thus of paramount importance. The current article presents an experimental modal analysis of a 200 MW Francis run...

Nowadays, hydropower plants are being used to compensate for the variable power produced by the new fluctuating renewable energy sources, such as wind and solar power, and to stabilise the grid. Consequently, hydraulic turbines are forced to work more often in off-design conditions, far from their best efficiency point. This new operation strategy...

The growing installation of intermittent renewable energy sources is forcing hydraulic turbines to work more frequently at speed no load when dangerous vaneless space vortex structures and stochastic flow phenomena can occur. An experimental campaign has been performed in a reduced-scale Kaplan turbine model at speed no load for different combinati...

Detecting fatigue cracks in hydraulic turbine runners is costly, as it requires stopping the unit, emptying it of water and accessing the runner for inspection. Thus, an alternative way based on monitoring the changes of the structural modal response induced by the formation and growth of a crack was investigated. To do so, the crack propagation in...

The operation of submerged rotating machines, such as marine current or tidal turbines, can present deleterious fluid phenomena that may provoke extreme structural vibrations. To predict their dynamic responses, it is necessary to know the added modal coefficients of their runners under a whirling motion. For that purpose, a bespoke test rig was de...

The current renewable energy market forces hydraulic turbines to operate for longer periods of time at off-design and transient conditions. Their life expectancy is then decreased due to the wear provoked by flow instabilities and stochastic flow excitations. This study presents an experimental investigation into the fatigue damage induced on the r...

The structural dynamic response of hydraulic turbines needs to be continuously monitored to predict incipient failures and avoid catastrophic breakdowns. Current methods based on traditional off-board vibration sensors mounted on fixed components do not permit inferring loads induced on rotating parts with enough accuracy. Therefore, the present pa...

The current paper presents an investigation into novel modal testing methods applied to a disk–shaft structure at different rotating speeds in air and water. The structure was excited using three different methods: an instrumented hammer, a piezoelectric PZT patch glued on the disk and a transient ramp-up. The structural response was measured using...

This paper presents the design and evaluation of an active control system to reduce vibrations and strains of submerged structures. For that, a metallic disk mounted in a test rig has been equipped with on-board waterproof strain gauges and accelerometers, to measure its structural response, and with an on-board PZT actuator patch, to provide the r...

The mesh significantly influences the quality of the numerical results in computational fluid dynamics (CFD) problems due to its correlation with turbulence models. In the present paper a structured mesh was generated using Gmsh and two semi-structured meshes were generated using snappyHexMesh to determine the suitable mesh distribution for simulat...

In the frame of the AFC4Hydro H2020 research project, an extensive measurement campaign has been carried out on a reduced scale Kaplan turbine model at the Vattenfall Research and Development facility in Älvkarleby, Sweden. The objective of the tests has been to monitor and characterize the dynamic response of the machine when it operates in propel...

The rotating vortex rope, which can be decomposed in the rotating and the plunging modes, is the origin of pressure fluctuations in the draft tube cone when hydraulic turbines operate at part load, compromising the structural integrity and limiting the output load. A measurement campaign was carried out in a Kaplan turbine model which is a replica...

This paper presents an experimental modal test of a Kaplan turbine model and provides the corresponding analysis of the results. The modal test of the rotor including the runner, the shaft and the generator was performed using, as exciters, an impact hammer and a shaker and, as sensors, several accelerometers. Additionally, numerical models of the...

Cavitating vortex shedding is a flow phenomenon commonly encountered behind bluff bodies in hydraulic machinery and systems. The generated vapor bubbles significantly change the dynamic behaviors of the vortices. In addition, the collapses of the cavities become major sources of unwanted effects such as vibration, noise and material erosion. In thi...

This present work devoted to simulate the unsteady cavitating flow around a hydrofoil and assess its erosion power predicted by different erosion risk indicators. For that, the behavior of unsteady cloud cavity is numerically reproduced using density corrected Shear Stress Transport (SST) k-ω turbulence model and the mass transfer between vapor and...

This paper proposes a new adaptive estimation approach to online estimate the model parameters of a piezoelectric cantilever beam. The beam behavior is firstly modeled using partial differential equations (PDE) considering the Kelvin-Voigt damping. To facilitate the estimation of unknown model parameters, the Galerkin’s method is introduced to extr...

The tip leakage vortex (TLV) has aroused great concern for turbomachine performance, stability and noise generation as well as cavitation erosion. To better understand structures and dynamics of the TLV, large-eddy simulation (LES) is coupled with a homogeneous cavitation model to simulate the cavitation flow around a NACA0009 hydrofoil with a give...

To accelerate the integration of fluctuating renewable energy technologies in the power systems, it is necessary to increase the flexibility of hydropower by operating turbines at off-design conditions. Unfortunately, this strategy causes deleterious flow phenomena such as von Kármán’s vortices at the wake of the vanes and/or blades. When their she...

The development of a methodology to simulate numerically the steady state flow field in Francis turbines was carried out using the open source CFD software OpenFOAM along with a MRF and AMI approach. A structured mesh obtained from previous studies was used with some modifications to solve the presence of imbalance points in the simulation. Numeric...

The present paper assesses the performance and characteristics of fiber Bragg grating sensors, with a special interest in their applications in hydraulic machinery and systems. The hydropower industry is turning to this technology with high expectations of obtaining high quality data to validate and calibrate numerical models that could be used as...

The present study intends to investigate numerically the impact of: i) the fluid added mass, ii) the turbine rotational speed and iii) the variation of the runner blade bearing stiffness due to the turbine water head on the modal response of a reduced scale Kaplan turbine. The impact of each variable has been quantified by means of a series of nume...

The transient cavitating flow in the wake of a hydrofoil at zero incidence angle has been simulated using a homogeneous mixture cavitation mass transfer model combined with both Reynolds Average Navier-Stokes (RANS) and Scale Resolving Simulation (SRS) turbulence models. The hydrofoil geometry corresponds to a 2D NACA 0009 with a truncated trailing...

The present study focuses on the numerical simulation of unsteadycavitatingflowaround a plane-convex hydrofoil withasemi-cylindrical obstacle, which is based on thecavitation-erosionexperimentperform atLMH-EPFLusing thevortex cavitation generatortunnel.The turbulence model k-𝜔SST SAS method, which presents advantages in terms of computational consu...

In order to better understand the fluid-structure interaction (FSI) in hydraulic machines, this study aims to numerically investigate the flow around an oscillating hydrofoil with special attention on the effect of unsteadiness on leading edge cavitation. The cavitating flow has been modelled as incompressible with a Shear Stress Transport (SST) tu...

An experimental investigation has been carried out to evaluate the performance of a cavitating Venturi flow. For that purpose, a closed loop circuit with a centrifugal pump and a transparent asymmetric converging-diverging test section has been built which allows to set the pressure level and the flow rate. The system is instrumented with several p...

Vortex cavitation can appear in the wake flow of hydrofoils, inducing unwanted consequences such as vibrations or unstable behaviors in hydraulic machinery and systems. To investigate the cavitation effects on hydrofoil vortex shedding, a numerical investigation of the flow around a 2D NACA0009 with a blunt trailing edge at free caviation condition...

A numerical investigation of the erosion aggressiveness of leading edge unsteady cloud cavitation based on the energy balance approach has been carried out to ascertain the main damaging mechanisms and the influence of the free stream flow velocity. A systematic approach has permitted the determination of the influence of several parameters on the...

The current study evaluates the effect of taking into account the second order term of the Rayleigh-Plesset equation for the numerical simulation of cavitation with homogeneous mixture models. For that, the corrected expression for the condensation mass transfer rate has been mathematically derived and implemented in the original Zwart and Singhal...

The numerical simulation of unsteady cavitation flows is sensitive to the selected models and associated parameters. Consequently, three Reynolds Average Navier-Stokes (RANS) turbulence models and the Zwart cavitation model were selected to assess their performance for the simulation of cloud cavitation on 2D hydrofoils. The experimental cavitation...

The present paper focuses on the numerical simulation of unsteady cavitation around a NACA66 hydrofoil to improve the understanding of the cavitation effects on hydraulic machinery. For this aim, the Zwart-Gerber-Belamri cavitation model was updated and uploaded as a library file for OpenFOAM's solvers using C++ language. Furthermore, the hybrid Re...

To have a safe structural design, an analysis of the dynamic behavior of a Francis turbine runner with consideration of the added mass effects of surrounding water is necessary during design phase. Both in design and at off-design operations, large-scale forms of attached cavitation may appear on runner blades and can change the added mass effects...

High-speed water tunnels are typically used to investigate the single-phase and two-phase flows around hydrofoils for hydraulic machinery applications but their dynamic behavior is not usually evaluated. The modal analysis of an NACA0009 hydrofoil inside the test section was calculated with a coupled acoustic fluid–structure model, which shows a go...

It has been found recently that the dynamic behavior of a cavitating hydrofoil is different from that in pure water in that, not only are the natural frequencies different, but the mode shapes may also change. In order to elucidate the mechanism behind this phenomenon, finite element simulations were carried out based on acoustic–structure coupling...

The influence of cavitation in water heating processes is still an unknown issue. To develop such knowledge, Universitat Politècnica de Catalunya-BarcelonaTech (UPC), in collaboration with the Spanish environmental engineering company Condorchem Envitech, S.L., has designed and built a new closed loop system to generate controlled cavitation in a V...

The dynamic response of an hydraulic machine is greatly affected by the water due to the added mass effect. However, the presence of cavitation can change the modal response of the coupled fluid-structure system because it modifies the properties of the surrounding fluid, i.e. the speed of sound and density. In this paper, a FEM-based acoustic-flui...

This paper describes the results of a comprehensive and ongoing project to control unsteady fluid-dynamic behaviour and associated effects at Svorka hydro power plant (25 MW, 260 m, 600 rpm), operated by Statkraft in Norway. This Francis unit had an original air admission system installed on the draft tube wall and turbine shaft. However, these sys...

The present study deals with the numerical study of the cavitation micro–jet velocity and erosionon on a plane–convex hydrofoil with semicylindrical obstacle, which induces a big cluster of cavitieswith a strong erosive power. The proposed model predicts micro-jet velocities based on energyconservation by assuming potential and kinetic energies at...

The added mass effects on a NACA0009 hydrofoil under cavitation conditions determined in a cavitation tunnel have been numerically simulated using finite element method (FEM). Based on the validated model, the effects of averaged properties of the cavity considered as a two-phase mixture have been evaluated. the simulation results point out that th...

Acoustic-Structural coupling methodology has been used to numerically investigate the failure of a Francis turbine runner that broke down within one day of operation. The goal of the work has been to determine the feasibility of a resonance condition under cavitating flow conditions. The obtained results prove that the presence of large vapor cavit...

A sample of healthy wind turbines from the same wind farm with identical sizes and designs was investigated to determine the average vibrational signatures of the drive train components during normal operation. The units were variable-speed machines with three blades. The rotor was supported by two bearings, and the drive train connected to an inte...

In this study, experimental and numerical analyses were performed to determine the effects of water loading on the axisymmetric modes of vibration of a circular plate. The plate was harmonically excited at its centre through an extension bar and its outer edge was left free. The Chladni technique, which involves exciting the plate at a resonance an...

The present study deals with the numerical study of the micro-jet velocity and the cavitation- erosion on an axisymmetric nozzle, which presents high flow unsteadiness and aggressiveness. The proposed model is based on energy conservation for the micro-jet velocity prediction, and assumes the potential and kinetic energies, at the start and at the...

A series of numerical simulations of the 3D cavitation development in the GAMM Francis turbine runner were carried out with the Zwart-Gerber-Belamri (ZGB) two-phase model available in ANSYS CFX v16.2. The aim of the investigation was to evaluate the influence of the ZGB parameters on the location, size and shape of the simulated cavitation. To begi...

The presence of air in piping systems is a major concern in the industry. Problems like flow disruption, reduction of hydraulic machinery efficiencies or a significant drop in pipe capacity are many times related to this fact. The present paper aims to find a simple and non-intrusive experimental method to detect air in piping systems. The method,...

The ALBA Synchrotron Light Source in Barcelona (Spain) requires a reliable, stable and adequate cooling system for its optimal operation. The current design with four long and intricate consumption lines with a ring type piping layout (270 m perimeter) and a common return pipe is believed to compromise the operability and to promote the trapping of...

Abstract The change of pipe natural frequencies due to added mass effects has been investigated in two cylindrical horizontal pipes from empty to completely water filled cases with various intermediate partially-filled conditions. The added mass coefficients of the three first vertical and horizontal modes of vibration have been determined with bot...

A fluid-structure interaction system has been solved using the coupled acoustic structural finite element method to simplify the cavitating flow conditions around a hydrofoil. The modes of vibration and the added mass effects have been numerically simulated for various flow conditions including leading edge attached partial cavitation on a 2D NACA0...

The prediction of erosion under unsteady cavitation is crucial to prevent damage in hydraulic machinery. The present investigation deals with the numerical simulation of erosive partial cavitation around hydrofoils.

Submerged structures that operate under extreme flows are prone to suffer large scale cavitation attached to their surfaces. Under such conditions the added mass effects differ from the expected ones in pure liquids. Moreover, the existence of small gaps between the structure and surrounding bodies filled with fluid also influence the dynamic respo...

The prediction of erosion under unsteady cavitation is crucial to prevent damage in hydraulic machinery. The present investigation deals with the numerical simulation of erosive partial cavitation around a NACA0015 hydrofoil. The study presents the calculation of the bubble collapse strength, Sb, based on the bubble potential energy to identify the...

The added mass effects on a NACA0009 hydrofoil under cavitation conditions determined in a cavitation tunnel have been numerically simulated using finite element method (FEM). Based on the validated model, the effects of averaged properties of the cavity considered as a two-phase mixture have been evaluated. The results indicate that the void ratio...

The present paper focuses on the erosive cavitation behavior around a plane convex hydrofoil. The Zwart-Gerber-Belamri cavitation model is implemented in a library form to be used with the OpenFOAM. The implicit large eddy simulation (ILES) is applied to analyze the three dimensional unsteady cavitating flow around a plane convex hydrofoil. The num...

The first three mode shapes of a cantilevered NACA0009 hydrofoil were experimentally investigated in air and under different flow conditions in a cavitation tunnel. First and second bending modes and first torsion mode were determined in resonance conditions with the hydrofoil vibrating in air, in still water, in flowing water or with leading edge...

A series of continuous vibration measurements in 14 upwind wind turbines of the same model and belonging to the same wind farm have been conducted. The data were acquired over a period lasting approximately half a year. The tower axial vibration acceleration has been monitored in the frequency band from 0 to 10 Hz with an accelerometer mounted on t...

Commercial programs are widely used to do unstructured and structured meshes for CFD simulations. However, grids and meshes based on free-open source software (FOSS) give to researchers and engineers the possibility to adapt and improve the meshing process for special study cases with a high Reynolds numbers, such as unsteady partial cavitating flo...

Investigations of attached partial cavitation are important because to prevent damages in hydrulic machinery and to reduce the costs. As expected computational fluid dynamics (CFD) methods have been developed for more than 40 years to understand this phenomenon and to improve the machinery designs, as pumps and hydraulic turbines. However, cavitati...

The prediction and control of cavitation damage in pumps, propellers, hydro turbines and fluid machinery in general is necessary during the design stage. The present paper deals with a numerical investigation of unsteady cloud cavitation around a NACA 66 hydrofoil. The current study is focused on understanding the dynamic pressures generated during...

A full-scale Francis turbine has been experimentally investigated over its full range of operation to detect draft tube swirling flows and cavitation. The unit is of interest due to the presence of severe pressure fluctuations at part load and of advanced blade suctionside cavitation erosion. Moreover, the turbine has a particular combination of gu...

The spectral content of the low frequency vibrations in the band from 0 to 10 Hz measured in full scale wind turbines has been statistically analyzed as a function of the whole range of steady operating conditions. Attention has been given to the amplitudes of the vibration peaks and their dependency on rotating speed and power output. Two differen...

a b s t r a c t A tissue machine suffering from Yankee chatter marks has been experimentally investi-gated. A series of vibration measurements during normal operation at various Yankee speeds on both the creping and the cleaning blade holders have been carried out. The anal-ysis in a frequency range up to 20 kHz has permitted to identify speed depe...

An experimental investigation has been carried out to quantify the effects of surrounding fluid on the modal behavior of a reduced scale pump-turbine impeller. The modal properties of the fluid-structure system have been obtained by Experimental Modal Analysis (EMA) with the impeller suspended in air and inside a water reservoir. The impeller has b...

The purpose of this research is implementing a continuous improvement initiative in terms of reliability, availability, maintainability and safety. This article presents a method with the goal of showing in which equipment, how and with which cost incidents related to maintenance appear in industrial plant equipment. The approach will be developed...