Titel Deelnemers "Korte inhoud" "Adjoint Shape Optimization based on Large Eddy Simulations through an Adaptation of the Reynolds-averaged Navier-Stokes Equations" "Giacomo Alessi" "Industrial design developments are more and more assisted by computer optimization algorithms to speed up the design process. As nowadays the real designs are close to their optimal configurations, the challenge lies in the extraction of the last percentages of improvement, thus accurate evaluations of the performance are required while maintaining the fast industrial time scales. The present thesis proposes a methodology to be used in this context. Initially, a classical adjoint shape optimization based on the Reynolds-averaged Navier-Stokes solution for the evaluation of the flow field has been implemented, in order to obtain a first optimal design at a low computational cost. This approach increases the design performance but could lead to a flawed evaluation of the flow characteristics. The correct prediction of the flow field is of crucial importance to drive numerical optimization to a real optimum design, thus a more accurate simulation is needed. An accurate evaluation of the flow field is ensured by the integration of Large Eddy Simulations in the optimization process, hereby avoiding the known convergence issues related to the chaotic flow motion. The computational cost associated with a more accurate prediction is kept to a minimum by reducing the number of expensive evaluations thanks to the use of a gradient based method in which the adjoint approach is used to evaluate the gradient of the objective function. The calculated gradients are linked to a node-based constrained morphing routine, allowing a large design freedom. The integration with a robust mesh morpher solver leads to successive automatic steps towards the design improvement. Design modifications take into account constraints and limitations. Finally, the feasibility of the design is guaranteed by the application of a smoother with the aim to avoid rough external surfaces. The routines developed have been applied to the optimization of the U-bend test case with the aim to reduce its pressure losses and consequently increase the performance of cooling systems of gas turbines. A validation against experiments has been performed to determine the accuracy of the numerical simulations." "Comparison of large eddy simulation and Reynolds-averaged Navier-Stokes evaluations with experimental tests on U-bend duct geometry" "Giacomo Alessi" "Experimental and Numerical Characterization of the Flow Field at the Core Entrance of a Water Model of a Heavy Liquid Metal-Cooled Reactor" "Philippe Planquart, Chiara Spaccapaniccia, Giacomo Alessi, Sophia Buckingham, Katrien Van Tichelen" "© 2018 International Topical Meeting on Advances in Thermal Hydraulics, ATH 2018 - Embedded Topical Meeting. All rights reserved. The thermal-hydraulics challenges of a nuclear reactor are numerous and mastering these is crucial for the design and safety of new reactors. Numerical simulation through computational fluid dynamics (CFD) codes or System Thermal-Hydraulics (STH) codes can address a lot of the different questions, nevertheless the use of water modeling for the study of the thermal-hydraulic behavior of a new primary system and the validation of codes remains an extremely valuable tool. A water model of the pool-type PbBi-cooled MYRRHA reactor has been developed at the von Karman Institute in collaboration with SCK•CEN. It is a full Plexiglas model at a geometrical scale 1/5 of MYRRHA. This transparent water model allows the application of optical measurement techniques, like Particle Image velocimetry (PIV) for the flow characterization. Local results of PIV measurements performed in the lower plenum at the entrance of the core are presented and compared with CFD results for a nominal operating condition and a natural convection case simulating the decay heat removal. A very good agreement has been found in the velocity field. The results also show the importance of the radial flow entering the core of the water model in natural convection." "Experimental investigation of accidental scenarios using a scale water model of a HLM reactor" "Philippe Planquart, Katrien Van Tichelen" "© 2019 Elsevier B.V. The thermal-hydraulics challenges of a nuclear reactor are numerous and their investigation is crucial for the design and safety of new reactors. Numerical simulation through CFD codes or System thermal hydraulics codes can address a lot of the different challenges; nevertheless the use of water modeling for the study and validation of the thermal hydraulic behavior of a new primary system remains a valuable tool. A water model of the pool-type liquid metal-cooled MYRRHA reactor has been developed at the von Karman Institute in collaboration with SCK•CEN. It is a full Plexiglas model at a geometrical scale 1/5 of the design version 1.2 of MYRRHA. The scaling was performed by respecting as much as possible the Richardson, Euler, Reynolds and Péclet numbers’ similarity with MYRRHA. This transparent water model allows the application of optical measurement techniques for the flow characterization. Different transient tests relevant for MYRRHA have been defined by SCK•CEN. These test cases have been studied using the water model facility. They include the study of the transient thermal hydraulic behavior when switching from forced to Loss-of-Flow (LOF), the failure of a single pump, the failure of one of the four heat exchangers and the loss of coolant inventory (LOC). Results of phenomenological behavior are presented as well as the time–dependent variation of temperatures recorded with different arrays of thermocouples immersed inside the upper plenum." "Numerical modeling of iron-based corrosion product oxides mass transport in the MYRRHA reactor during normal operation" "A Marino, S Buckingham, K Gladinez, S Keijers, P Planquart, Katrien Van Tichelen, A Aerts" "© 2018 Elsevier B.V. To support the design of an external filtering and conditioning system for the lead-bismuth cooled MYRRHA reactor, the formation and transport of iron oxide particles from corrosion products in the reactor primary system have been investigated for normal operating conditions. The regions of the reactor with the highest probability of oxide formation are identified by a local chemical equilibrium model for magnetite formation. This analysis reveals that magnetite precipitation generally occurs in regions with large temperature gradients. For the specific case of the MYRRHA reactor, these regions correspond to the transition region between the barrel and the upper plenum, mainly at the location of the holes in the top part of the barrel. The transport behaviour of solid oxides from these regions is then investigated with a multi-phase Euler-Lagrange particle tracking model of the MYRRHA primary system. The simulations show that the majority of large oxide particles (above 100 µm) will eventually move to the free surface without passing through the reactor core, thereby allowing their removal by an external filtering system with surface extraction. This indicates that such large particles present a minimal risk for sudden core blockage, which does not compromise reactor safety. On the other hand, particles below a threshold diameter identified at 40 µm cannot be efficiently filtered out by an external system since the majority follows the carrier liquid and re-enters the core during each LBE flow-through cycle. The continuous purification of the coolant is therefore necessary to avoid undesired build-up of suspended particles in the primary system. A preliminary design value of the required mass flow rate through the filters is identified with the support of numerical simulations." "Porous and geometry-resolved CFD modelling of a lattice transmission tower validated by drag force and flow field measurements" "Jonas Allegrini, Jan Maesschalck, Giacomo Alessi, Gertjan Glabeke, Julien Christophe, Jeroen van Beeck" "Predicting modal characteristics of a cluster of cylinders in axial flow: From potential flow solutions to coupled CFD-CSM calculations" "Jeroen De Ridder, Joris Degroote, Katrien Van Tichelen, Jan Vierendeels" "© 2017 Elsevier Ltd External fluid flow has a number of effects on the dynamics of a submersed structure: e.g., a solitary cylinder exposed to an external flow experiences added mass and damping due to the presence of the surrounding fluid. At high axial flow velocities relative to the stiffness of the cylinder, coupled instabilities such as flutter and divergence occur. Compared to a solitary cylinder, a cluster of cylinders also experiences inter-cylinder coupling: pressure perturbations in the fluid due to the movement or acceleration of one cylinder force another cylinder to move. Consequently, the different cylinders can move in organized patterns. In this contribution, modal characteristics of a 7-rod bundle will be predicted by linear theory as well as by coupled CFD–CSM (Computational Fluid Dynamics — Computational Structure Mechanics) calculations. In the first part, fluid forces which lead to coupling of motion are computed with classical potential flow theory and URANS (Unsteady Reynolds-Averaged Navier–Stokes). Those forces are divided in a contribution in phase with the acceleration and a contribution in phase with the velocity of a cylinder. In the second part, modal characteristics of a 7 cylinder bundle are computed with coupled CFD–CSM simulations. The initial perturbations, which are required for the time-domain simulations come from a simplified structural model, with potential flow coupling between cylinders. The results are compared to linear theory. In the final part, approximations are proposed to predict upper and lower bounds of eigenfrequencies and damping, using calculations with only one cylinder." "Thermal-hydraulic study of the LBE-cooled fuel assembly in the MYRRHA reactor: Experiments and simulations" "Katrien Van Tichelen" "© 2016 Elsevier B.V. Heavy liquid metals (HLMs), such as lead-bismuth eutectic (LBE) and pure lead are prominent candidate coolants for many advanced systems based on fast neutrons. In particular, LBE is used in the first-of-its-kind MYRRHA fast reactor, to be built in Mol (Belgium), which can be operated either in critical mode or as a sub-critical accelerator-driven system. With a strong focus on safety, key thermal-hydraulic aspects of these systems, such as the proper cooling of fuel assemblies, must be assessed. Considering the complex geometry and low Prandtl number of LBE (Pr ∼ 0.025), this flow scenario is challenging for the models used in Computational Fluid Dynamics (CFD), e.g. for relating the turbulent transport of momentum and heat. Thus, reliable experimental data for the relevant scenario are needed for validation. In this general context, this topic is studied both experimentally and numerically in the framework of the European FP7 project SEARCH (2011–2015). An experimental campaign, including a 19-rod bundle with wire spacers, cooled by LBE is undertaken at KIT. With prototypical geometry and operating conditions, it is intended to evaluate the validity of current empirical correlations for the MYRRHA conditions and, at the same time, to provide validation data for the CFD simulations performed at NRG. The results of one benchmarking case are presented in this work. Moreover, this validated approach is then used for simulating a complete MYRRHA fuel assembly (127 rods)."