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Within the study of fluid-elastic instability in heat exchangers tube banks, a considerable theoretical and experimental effort has been produced for understanding fluid–structure coupling in two-phase flow. This communication discusses the commonly accepted added mass modeling and proposes some ways of further improvement. Notably, it turns out that added mass may be overestimated in a two-phase flow. Taking into account this phenomenon improves the collapsing of flow-induced forces data.

Physical modelling computation, virtual reality, instrumentation and data analysis have shown great progress in the past years. Thus, the integration of all these disciplines in one unique tool seems now achievable. Within this frame, this communication aims at discussing the extension of the Digital Twin concept to the PWR Steam Generators. Operating steam generators communicate some information on their health status during inspection outages, and some other during operation. As, generally speaking, a SG fully satisfies its role of safely produce steam, the goal of an in-service DT is to optimize both the maintenance and the operation, namely: provide the best preparation for next outages, avoid SG-caused unscheduled outages and obtain the best performances. Some general features are outlined with respect to the different roles of Digital Twins both in design and operation. Then the vision of the R&D Division of EDF Company is given for the developed Steam Generators Digital Twin. Two use cases are presented focusing on maintenance. The first one is about chemical cleaning schedule including how the Digital Twin contributes to the prediction of shell side deposit, and the second one is about periodic hydraulic test preparedness, including how the digital twin contributes to the prediction of crack sizes.

Two-phase flow head losses across tube support plates in U-bend tube steam generators are classically evaluated from single phase head losses duly modified with a correction factor to account for two-phase effects. This communication reports upon a series of experiments to feed head loss models for clogged tube support plates under two-phase flow. By using a classical approach, a single phase head loss model is used together with a two-phase flow multiplier. The experiments cover a large span of clogging levels, up to the unrealistic limit case of 95% of clogging. Singular head loss due to the tube support plate is measured under single-phase flow for clean and clogged plates. The head loss factor is hence evaluated and compared to the prediction of some available models. Then the same experiment is repeated under two-phase flow condition. By combining the previously measured single-phase factor with the two-phase flow measurements, recommendations for predicting two-phase flow multiplier with existing models are given.

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators and designers of nuclear power plants. In order to predict damages due to such vibrations, predictive calculations are performed, both by designers and by operators, which allow one to evaluate safety margins and thereafter to optimize the SG maintenance policy. In cases when semi analytical models of fluid-dynamic forces are used, together with corresponding dimensionless fluid force coefficients, closures are assessed by experiment. The database of dimensionless coefficients should then cover relevant tube bundle configurations. Within this framework, a test rig which was available at EDF was modified in order to arrange different pitch-to-diameter ratio bundles and different tube diameters. This paper discusses the fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.

Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. Electricité de France (EDF) has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy. The software is based on a semi-analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was operated with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions in order to represent the so-called in-plane and out-of-plane vibrations. This paper outlines the experimental results and some detailed physical analysis of some selected points of the experiment series: the response modes are identified by means of operational modal analysis (OMA) (i.e., under unmeasured flow excitation) and presented in terms of frequency, damping, and mode shapes. Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluid-elastic instability (FEI).

Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. EDF has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was presented in previous PVP conferences with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions. This paper presents some extended physical analysis applied to some selected points of the aforementioned experiment series: the response modes are identified by means of operational modal analysis (i.e. under unmeasured flow excitation) and presented in terms of frequency, damping and mode shapes. Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluidelastic instability.

Since steam generators are used, many experiments have been performed to understand the different phenomena appearing in them. One of the main issues to reproduce a similar flow on a reduced-scale experiment is the choice of the two-phase mixture. Air/water and boiling freon are among the most used two-phase flow mixtures. In the present document, a finite-volume CFD code dedicated to multi-phase flows based on a two-fluid approach (extended to n) is used to compare two mixtures numerically. Thanks to two experiments, an air/water horizontal channel and a freon/freon inclined tube bundle, a first part highlights the validity of the two-phase flow modeling. Then, based on inlet superficial velocities from both experiments, a numerical experiment is performed by using each mixture on the other experiment. Void fraction profiles and two-phase flow regimes are compared in order to exhibit the behaviors of both mixtures in a steam generator like tube bundle. Results turn out to provide useful information (void fraction profiles mainly) about mixture properties, and near-wall loads in the vicinity of cylinders are investigated.

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to evaluate safety margins and thereafter to optimize the SG maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is progressively updated in order to cover most of existing tube bundle configurations. Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.

The unsteady flow motions and the force distribution in a normal square tube array subject to cross-flow induced vibrations are investigated by means of large-eddy simulations. The flow configuration and the operating conditions are taken from the experiments of Gosse et al. (PVP Conference, 2001). The set-up is made of 63 (9 rows and 7 columns) straight tube bundle. The tubes are arranged in a square in line pattern, and a cell of 9 flexible tubes, located in the middle of the bundle, may translate in the drag and lift directions. The LES of cross-flow induced vibrations of a cell of 9 flexible tubes in a normal square tube array is performed. A fully-coupled fluid-structure calculation is hence achieved using Code_Saturne, an open source CFD tool. Turbulence modeling is achieved using the large-eddy simulation framework based on the so-called classical Smagorinsky model. The tube dynamics is modeled by simple mass-spring-damper systems, and the motions of the fluid domain is accounted for by a moving mesh technique (Arbitrary-Lagrangian-Eulerian formulation). The consistency of the calculations is demonstrated by comparing the numerical data to the experiments of Gosse et al. (PVP Conference, 2001) in terms of tube amplitude and flow-induced force spectra, for various gap velocities. Investigation of the spectra of the flow-induced forces then shows that the tube motions ignite the emergence of flow phenomena at constant Strouhal numbers. The fluid-structure interactions are also responsible for the existence of a series of tones at rather constant frequencies, corresponding to the vibrational modes of the flexible cell.

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to asses risk and thereafter to optimize the SG maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is updated in order to cover all existing tube bundle configurations. Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the result of the first phase of the associated experiments in terms of force coefficients and two-phase flow excitation spectra for both in-plane and out-of-plane vibration.

Flow-induced vibrations of Steam Generator (SG) tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to evaluate safety margins and thereafter to optimize the SG maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is steadily updated in order to cover all tube bundle configurations found in EDF power plants. Within this framework, we present a new test rig dedicated to the parallel triangular tube arrangement submitted to a two-phase cross-flow. A new test loop is constructed as well, allowing fluid-elastic instability to be induced on the test rig for various qualities. The details of the experimental arrangement are presented together with the preliminary validation tests.

The cross-flow induced vibrations in water of a single flexible tube in a normal square array of rigid tubes are investigated by means of large-eddy simulations, based on the classical Smagorinsky model. The flow configuration and the operating conditions are taken from the experiments of Granger et al. (J. Fluid Struct., 1993). A fully-coupled fluid-structure calculation is hence performed: the tube dynamics is modeled by a mass-spring-damper system, and the motion of the fluid domain is accounted for by a moving mesh technique. The numerical results are compared to the experimental data in terms of amplitude and frequency of the flexible tube oscillations, for various inflow velocities. In addition, characteristics of the flow-induced forces are discussed: features of the power spectral densities of lift and drag forces, such as the envelope spectrum or the spanwise correlation length are investigated.

This paper reports an experimental investigation of the high-Reynolds number turbulent flow past a thin flat plate with sharp untapered edges, by means of tomographic PIV. The experiments, carried out in the S4 wind tunnel of IMFT, have quantified the three-dimensional coherent vortex structures, by means of 3-D Proper Orthogonal Decomposition and reconstruction. The interaction of the most energetic coherent structures with the random turbulence is discussed. Furthermore, Proper Orthogonal Decomposition (POD), analysis allowed evaluation of three-dimensional phase-averaged dynamics that quantified the vortex shedding mechanism as well as the influence of higher modes associated with the finer-scale turbulence.

International audience; In this manuscript a simple Lumped Parameter model, developed in order to study the interaction between water droplets and a hydrogen–air flame, has been presented. A parametric study has been described and the results given by the proposed model are discussed in the paper. In addition, the description of an experimental facility designed to study these thermodynamics aspects is reported here. In particular, the nozzles of the spray system of the facility have been characterized in terms of drop size distribution.

In case of severe accident, complex thermal-hydraulics phenomena are expected to occur in the containment atmosphere. To investigate and understand these phenomena, fundamental for nuclear safety and design, major efforts are being spent all over the world. A new OECD project, named SETH-2, is conceived to generate relevant experimental data, useful to improve the modeling capabilities of the computer codes aimed to predict post-accident containment thermal-hydraulic conditions. The Commissariat a l’Energie Atomique (CEA) contributes to the project performing experiments within the large scale MISTRA facility. Tests are proposed to investigate mixing phenomena promoted in a stratified containment. In particular, one of these test series concerns the interaction of buoyant jets with a stratified atmosphere. The present work is aimed to develop and validate computational tools useful to support the design of this experimental campaign and to analyze the actual MISTRA tests. In this aim, two different models have been implemented for turbulent buoyant jets in a stratified atmosphere: an engineering analytical model for a fast characterization of flow structures and a finite elements computational fluid dynamics (CFD) model that allows a detailed analysis of local phenomena. The models have been successfully validated for vertical buoyant jets in uniform atmosphere. Further experimental and numerical activities are illustrated, aimed to carry out the validation with stratified atmosphere and inclined injections.Copyright © 2008 by ASME

The present study aims at a physical analysis of the coherent and chaotic vortex dynamics in the near wake around a flat plate at incidence, to provide new elements in respect of the flow physics turbulence modelling for high-Reynolds number flows around bodies. This constitutes nowadays a challenge in the aeronautics design. A special attention is paid to capture the thin shear layer interfaces downstream of the separation, responsible for aeroacoustics phenomena related to noise reduction and directly linked to an accurate prediction of the aerodynamic forces. The experimental investigation is carried out by means of tomographic PIV. The interaction of the most energetic coherent structures with the random turbulence is discussed. Furthermore, the POD analysis allowed evaluation of 3D phase averaged dynamics as well as the influence of higher modes associated with the finer-scale turbulence. The numerical study by means of the Organised Eddy Simulation, OES approach ensured a reduced turbulence diffusion that allowed development of the von Karman instability and of capturing of the thin shear-layer interfaces, by using appropriate criteria based on vorticity and dissipation rate of kinetic energy. A comparison between the experiments and the simulations concerning the coherent vortex pattern is carried out.

Under specific conditions, a secondary flow can develop from a laminar horizontal buoyant jet released through a round nozzle. This secondary flow is a veil-shaped plane plume, which detaches from the main jet. The conditions for its apparition have been empirically determined and are available in the open literature. This paper aims to give theoretical basis to these conditions and to show some novel experimental observations and measurements on horizontal buoyant jets with secondary plume. One of the main results is the identification of the persistence of transversal velocity components in the release section of horizontal buoyant jets.