Detached Eddy Simulation of Restricted Shock Separated flow in a Thrust Optimized Contoured nozzle

Detached Eddy Simulation of restricted shock separated (RSS) flow has been performed to understand the physics of complex cap-shock pattern, which is the key cause of separated flow transition in the rocket nozzles. High-order shock-capturing numerical schemes are necessary to understand this complex flow. Hence a fifth order monotonicity preserving weighted essentially non-oscillatory (MPWENO) scheme is used here for good numerical resolution

Thermal mixing in a T-junction: Novel CFD-grade measurements of the fluctuating temperature in the solid wall

International audienceThis article reports new experiments performed with the purpose of generating novel data of the fluctuating temperature inside the solid in the mixing region between hot and cold water in a T-junction. This data has been measured using a novel sensor (coefh) developed at the Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA) in Cadarache, France. These experiments are performed within the framework of the MOTHER project. The main objective of the MOTHER project is to validate various CFD approaches (such as LES, Hybrid i.e. RANS/LES and RANS) for transient heat transfer in a T-junction configuration including the pipe wall. Hence, the performed experiments have focused on accurately measuring and documenting the boundary conditions to be able to have a well-defined database for CFD validation. The tests are performed for two different Reynolds numbers 40000 and 60000 and for two different T-junction geometries; a sharp corner and a round corner

Statistical Evaluation of the Shock Wave Boundary Layer Interaction Phenomenon

Turbulent velocity and thermal correlations from direct numerical simulation data of a spatially growing compressible turbulent boundary layer interacting with an impinging shock are discussed. The cross-stream variation of the velocity second-moments and the thermal fluxes one boundary layer thickness upstream of the shock impingement point are discussed. Other correlations are examined to further statistically quantify the effect of the oblique shock-turbulence interaction

Fluid-structure interaction of a 7-rods bundle : benchmarking numerical simulations with experimental data

Fluid flows through rod bundles are observed in many nuclear applications, such as in the core of Gen IV liquid metal fast breeder nuclear reactors (LMFBR). One of the main features of this configuration is the appearance of flow fluctuations in the rod gaps due to the velocity difference in the sub-channels between the rods. On one side, these pulsations are beneficial as they enhance the heat exchange between the rods and the fluid. On the other side, the fluid pulsations might induce vibrations of the flexible fuel rods, a mechanism generally referred to as Flow Induced Vibrations (FIV). Over time, this might result in mechanical fatigue of the rods and rod fretting, which eventually can compromise their structural integrity. Within the SESAME framework, a joint work between Delft University of Technology (TU Delft), Ghent University (UGent), and NRG has been carried out with the aim of performing experimental measurements of FIV in a 7-rods bundle and validate numerical simulations against the obtained experimental data. The experiments performed by TU Delft consisted of a gravity-driven flow through a 7-rods, hexagonal bundle with a pitch-to-diameter ratio P/D = 1.11. A section of 200 mm of the central rod was made out of silicone, of which 100 mm were flexible. Flow measurements have been carried out with Laser Doppler Anemometry (LDA) whereas a high-speed camera has measured the vibrations induced on the silicone rod. The numerical simulations made use of the Unsteady Reynolds-averaged Navier-Stokes equations (URANS) approach for the turbulence modelling, and of strongly coupled algorithms for the solution of the fluid-structure interaction (FSI) problems. The measured frequency of the flow pulsations, as well as the mean rod displacement and vibration frequency, have been used to carry out the benchmark

Contribution à la simulation numérique des décollements d'écoulements turbulents induits par choc. Application à l'écoulement sur-détenu de tuyère supersonique

Shock-induced flow separation and reattachment are encountered in many configurations, such as supersonic inlets, transonic airfoils or rocket nozzles. These phenomena involve complex interactions of boundary layers with compression or expansion waves and exhibit a low-frequency unsteady behaviour which still requires a clear explanation. This study aims at better identifying the physical mechanisms which drive the global structure of these flows and suggesting improved numerical tools in order to predict these more accurately. The appearance of free and restricted separations in supersonic annular jets occuring in thrust optimised contour nozzles operating in overexpanded conditions is more particularly investigated while various hypothesis are tested to explain the evolution of the associated unsteady asymmetric wall pressure field in function of the nozzle pressure ratio. The numerical strategy proposed relies on a realizable extension of the Detached Eddy Simulation, combined with high order shock capturing schemes and an implicit time integration algorithm. This methodology is applied for a wide range of both constant or transient inflow conditions and leads to identify more accurately the appearance of free and restricted separations and the time-varying morphology of the flow during the transition process. For both regimes, the simulation is carried out for long-enough time to perform reliable statistical analysis and azimuthal expansion of the wall pressure field and thus investigate extensively the possible origins of the side-load activities.Les décollements d'écoulement induits par choc et leur éventuel réattachement sur paroi sont observés dans de nombreuses configurations d'intérêt pratique, incluant les entrées d'air, les profils transsoniques ou les tuy`eres de lanceurs spatiaux. Ces phénom`enes mettent en jeu des interactions complexes entre couches limites et ondes de choc ou de détente conduisant à des instationnarités à basses fréquences dont l'origine reste aujourd'hui à élucider. Cette étude vise d'une part à proposer une stratégie numérique permettant de prévoir plus précisément ces phénom`enes de décollement et d'autre part d'identifier les principaux mécanismes physiques qui pilotent l'évolution de leur structure globale. L'étude porte plus particuli`erement sur les configurations de décollements libres ou séparés apparaissant en tuy`ere optimisée en poussée opérant en régime surdétendu. Différents mod`eles phénoménologiques sont ainsi testées pour décrire l'évolution du champ de pression instationnaire et dissymétrique en fonction du niveau de surdétente. La stratégie numérique proposée repose sur la combinaison de schémas à capture de choc d'ordre élevé (WENO 5), d'algorithmes d'intégration implicite en temps et d'une modélisation de la turbulence étendant l'approche Detached Eddy Simulation via l'ajout de corrections de réalisabilité. Une large plage de niveaux de surdétente est considérée, à la fois en condition d'entrée stabilisée et transitoire, afin de clarifier les conditions d'existence des différents régimes de décollements libres et restreints, ainsi que l'évolution temporelle de la morphologie globale de l'écoulement transitant entre ces deux régimes. L'évolution instationnaire de l'écoulement est simulée sur des temps suffisamment longs pour permettre une analyse spectrale des contributions des premiers modes azimutaux à la dynamique basse fréquence du champ de pression pariétale

Numerical Investigations of a Two-Way Coupled Fluid–Structure Interaction Approach for Fast Transients in Fluid-Filled Flexible Piping Systems

International audienc

Contribution to the numerical simulation of turbulent shock-induced separated flows, application to supersonic over-expanded nozzle flow

Les décollements d'écoulements induits par choc et leur éventuel réattachement sur paroi sont observés dans de nombreuses configurations d'intérêt pratique, incluant les entrées d'air, les profils transsoniques ou les tuyères de lanceurs spatiaux. Ces phénomènes mettent en jeu des interactions complexes entre couches limites et ondes de choc ou de détente conduisant à des instationnarités à basse fréquence dont l'origine reste aujourd'hui à élucider. Cette étude vise à proposer une stratégie numérique permettant de prévoir plus précisément ces phénomènes de décollement et à identifier les principaux mécanismes physiques qui pilotent l'évolution de leur structure globale. L'étude porte plus particulièrement sur les configurations de décollements libres ou séparés apparaissant en tuyère optimisée en poussée opérant en régime sur-détendu. La stratégie numérique repose sur la combinaison de schémas d'ordre élevé (WENO 5), d'algorithmes d'intégration implicite en temps et d'une approche Detached Eddy Simulation (DES) incluant des corrections de réalisabilité pour la modélisation de la turbulence. Une large plage de niveaux de sur-détente et des temps longs de simulation sont considérés, à la fois en condition d'entrée stabilisée et transitoire, afin de clarifier les conditions d'existence des différents régimes de décollements libres et restreints, ainsi que l'évolution temporelle de la morphologie globale de l'écoulement transitant entre ces deux régimes. L'évolution instationnaire de l'écoulement est simulée sur des temps suffisamment longs pour permettre une analyse spectrale des contributions des premiers modes azimutaux à la dynamique basse fréquence du champ de pression pariétale.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Development and application of computational fluid dynamics approaches within the European project THINS for the simulation of next generation nuclear power systems

Today computational fluid dynamics (CFD) is widely used in industrial companies, research institutes and technical safety organizations to supplement the design and analysis of diverse technical components and large systems. Such numerical programs are applied to better understand complex fluid flow and heat transfer phenomena. In the last decades there is an increasing interest in the nuclear community to utilize such advanced programs for the evaluation of different nuclear reactor safety issues, where traditional analysis tools show deficiencies. Within the FP7 European project THINS (Thermal Hydraulics of Innovative Nuclear Systems), CFD and coupled 1D-3D thermal-hydraulic simulations are being carried out. These are dedicated to the analysis of the thermal-hydraulics of gas, liquid metal and supercritical water cooled reactors. Such concepts utilize innovative fluids, which have different properties from the ones used in the current nuclear reactors. In order to improve the thermal-hydraulic predictions of their behavior, CFD development, application and validation activities are performed within THINS. This overview paper highlights some of the CFD related work within the European project