The physics and modeling of air ejectors in on- and off-design conditions have been extensively addressed in the past, reaching a good level of maturity. However, to achieve a robust dynamic model at the system scale integrating an ejector, there is a need to develop 0D models suitable for tackling abnormal functioning modes and the transition between them.The current research focuses on understanding the physical behavior of air ejectors for aeronautical applications. First, the operational envelope with relevant modes and transitions is presented. Hence, an experimental set-up is built to allow direct observation of transient phenomena under typical aeronautical conditions. Complementarily, CFD (RANS and URANS) simulations are employed to gain knowledge of the whole operational envelope, including abnormal modes. Experimental analysis and CFD are employed to show the ejector’s quasi-steady behavior under the system’s time-scale.As a final milestone, a 0D model previously implemented is here extended and calibrated using CFD simulations to cover abnormal functioning scenarios as primary closed mode and inverted operation. Finally, some typical transitions belonging to the operational envelope are reproduced and validated compared to experimental data, and the robustness of the Modelica implementation is highlighted.

Investigating Fiber Bragg Gratings (FBG) behavior in varied fluid environments for temperature measurements. Analysis includes secondary effects and liquid metal influence on peak spectrum.

The interaction between cooling fluid and solid structures (rods, tubes) in nuclear power plants may lead to flow-induced vibrations (FIV), causing material fatigue, fretting wear, and eventually loss of component integrity. This can cause further safety issues as well as substantial standstill costs due to longer or unplanned outages. With the growing computational power, the application of modern 3D numerical simulation tools for the accurate prediction of FIV phenomena is rapidly increasing. In 2022, the GO-VIKING ( G athering expertise O n V ibration I mpa K t I n N uclear power G eneration) project received a grant within the Horizon Europe research and innovation funding program. Sixteen European and two US partners started their collaboration in the field of FIV experiments and analysis. Over four years, the GO-VIKING project investigates FIV phenomena occurring in nuclear reactor cores and steam generators under single- and two-phase flow conditions. The project’s main objectives are to expand the expertise in the field of FIV through generation of new experimental and high-resolution numerical data; development, improvement, and validation of fluid-structure interaction (FSI) methods for FIV evaluation; training stakeholders in the application of these methods; and synthesizing guidelines for the prediction and assessment of FIV phenomena in nuclear reactors. This paper provides an overview of the GO-VIKING objectives, scientific program, as well as of the main scientific achievements in the first project year.

We present the calibration of a 1D ejector model on experimental data from a large-scale ejector facility at the von Karman Institute. The facility allows for adjusting the inlet pressures (with pressure ratios up to 5) and temperatures (with temperature ratios up to 1.6) and producing mass flow rates up to 0.7 kg/s. The experimental data are used to calibrate an ejector model consisting of two interacting 1D domains based on the compound choking theory. The model closure is carried out in terms of friction factor for the primary flow and a variable loss coefficient for the secondary flow. These were successfully linked to the ratios of inlet and outlet pressures, allowing the calibrated model to predict both mass flow rates with 10 % accuracy.

Turbulent heat fluxes (THFs) estimation is of paramount importance in the determination of heat transfer in fluids. Numerical models for low Prandtl number fluids are still unreliable and their experimental evaluation is a challenging task since it requires simultaneous measurement of fast velocity and temperature fluctuations. In nuclear applications, a better understanding of THFs in liquid metals could lead to more precise predictions of the primary coolant temperature for the evaluation of nominal operation (forced convection regime) and accidental conditions (mixed and/or natural convection regime). The first part of this work focuses on the selection of the measurement techniques suitable for water, GaInSn and LBE and the thorough literature review required. Tests in different setups led to the choice of sheathed type K thermocouples and fiber Bragg gratings for temperature measurements and Ultrasound Doppler Velocimetry and Hot Wire Anemometry for velocity measurements. The comparison carried out among the different techniques underlines advantages and limitations of each of them. Calibration of each technique is performed and cross-effects of temperature and velocity are evaluated. Uncertainty analyses are also carried out. To conclude, first results obtained in a differentially heated cavity made of stainless steel 316L with an edge of 60 mm are presented. DNS numerical simulations are performed to know the ranges of the quantities to be measured and to have results available for comparison with experiments.

The integration of large size Ultra High Bypass Ratio (UHBR) engines introduces new restrictions of space for their integration with the aircraft wing. Under this scenario, a reduction of the size of the bleed air system and particularly of the pre-coolers is requested. The current research aims to introduce air-air ejectors as a potential solution. A combined methodology based on experimental and CFD analyses is proposed to obtain physical insights and validation material for the development of a robust and accurate lumped model, capable of simulating the static and dynamic ejector behaviour in normal and abnormal conditions. In this paper, an overview on the performed initial activities on the dynamic aspects is provided.

The increased use of electrothermal ice protection systems (ETIPSs) in various industries (manned and unmanned aviation, energy production) requires improvements to de-icing efficiency, ice shedding predictability, and energy consumption. To achieve these, a coupled numerical and experimental investigation of ETIPS’s ice removal (ice shedding) mechanism is presented in this paper. Idealized ETIPS de-icing experiments performed in the icing wind tunnel of the von Karman Institute show several ice shedding mechanisms. A one-dimensional phase change solver developed for ice melting simulations highlights the water layer thickness influence over the ice shedding process. Coupled numerical–experimental results are employed to develop an idealized ice shedding model. The model is validated in realistic de-icing experiments in a second experimental campaign in the icing wind tunnel of the LeClerc Icing Research Laboratory.

The aim of this paper is to characterize the sloshing regimes in a cylinder and to statistically study the chaotic transition close to the natural frequency. The study was motivated by the lack of experimental data close to the chaotic transition. Using a dedicated shaking table called SHAKESPEARE, a statistical study was performed to exhibit a specific trend close to the transition. The performed tests were compared to the literature and show a slight difference which could be due to a different position of the probes. Close to the transition, a "plateau" in the amplitude of the free surface was observed and characterized using a phase portrait. It shows an elliptical limit cycle dependent on the test conditions. It is especially dependent on the starting point (still or moving water) which was studied in this paper. A later transition position was then observed when applying a frequency at the beginning of the test to break the "still water" assumption.

The increasing interest in Small Air Transportation (SAT), to enhance global connectivity, is highlighting the need for reducing take-off distance: lift coefficient has to be increased without penalizing the configuration drag, weight and complexity. Within the EU Clean Sky 2 projects, a blown flap configuration has been developed to allow STOL capabilities of a future affordable and green commuter belonging to EASA CS 23. The blowing system design choice is aimed at keeping the inevitable associated increase in pitching moment very low, and not penalizing performance when blowing fails. In collaboration between Piaggio Aerospace and the MOTHIF consortium, a wing model was designed, built and tested in the VKI’s large subsonic L1-A wind tunnel, reproducing bi-dimensional preliminary results obtained during the design phase. In order to reduce and predict three dimensional and blockage effects, CFD has been used extensively to obtain a proper test chamber configuration and to reproduce some wind tunnel test results, so that both the accuracy of wind tunnel and design methodology can be assessed. This work presents the comparison between experimental data and CFD simulations to demonstrate the usefulness of simulations to reduce both the risk for erroneous results in experimental activities and their related cost.

The renewed interest in reusable launch vehicles has fueled the development of many advanced space transportation concepts. An interesting method for recovering rocket stages called ’In-AirCapturing’, has been patented by DLR. The winged stages are captured mid-flight and towed back to the landing site by an aircraft, eliminating the need for an additional propulsion system. A critical procedure in the capturing process involves an aerodynamically controlled capturing device attached by a rope to the towing aircraft, performing an autonomous rendezvous maneuver with the launch vehicle. In this paper, the complex dynamics associated with this phase are modelled and examined. This includes the aerodynamics of the capturing device, external disturbances like the turbulent wake of the aircraft and the flexible dynamics associated with the rope. These effects are combined into a multidisciplinary framework and a preliminary control system is proposed. The final open-loop simulation results provide valuable information about the stability and controllability of the system, which will be used for advanced control design in future work.

The E-SCAPE (European SCAled Pool Experiment) facility at the Belgian nuclear research center SCK center dot CEN is a thermal hydraulic 1/6th-scale model of the MYRRHA reactor with an electrical core simulator and cooled by LBE. The E-SCAPE facility provides experimental feedback to the designers on the forced and natural flow patterns, flow mixing and stratification during operational and accidental conditions. In addition, it provides valuable data for validation of the computational techniques for their use with LBE and in the design of MYRRHA. In terms of momentum field, one of the most important integral quantity to reproduce is the pressure drop in the system which has a direct consequence on the evolution of the mass flows and determines the free-surface levels in transient scenarios. In this paper, a detailed CFD study is performed on the flow in the E-SCAPE core region with the aim on predicting the correct pressure drop. Different numerical representation of the core geometry have been modeled and subjected to validation against experimental results from E-SCAPE. Special attention has been addressed to the choice of geometric simplifications and numerical models for accurate representation of the core of the E-SCAPE pool facility.

The Belgian Nuclear Research Centre (SCK center dot CEN) is at the forefront of heavy liquid-metal (HLM) nuclear technology worldwide with the development of the Multi-purpose hYbrid Research Reactor for High-tech Applications (MYRRHA) accelerator-driven system. MYRRHA is a flexible fast-spectrum pool-type research reactor cooled by lead bismuth eutectic (LBE) and has been identified as the European Technology Pilot Plant for the lead-cooled fast reactor. Given the innovative nature of MYRRHA, the project is currently going through a prelicensing phase. The MYRRHA research and development (R&D) program is driven by this prelicensing process and aims to fill the existing gaps in knowledge with respect to LBE chemistry, material behavior, fuel behavior, instrumentation, and HLM thermal hydraulics. In this critical review we present selected topics from the R&D program on HLM thermal hydraulics that are essential for the design, engineering, and safety analysis of MYRRHA and other HLM-cooled reactors. The topics addressed include turbulent heat transfer in HLM, fuel assembly thermal hydraulics and flow-induced vibrations, control rod hydrodynamics, primary heat exchanger pool and integral system thermal hydraulics, sloshing, and multiphysics modeling.

Although ice shedding generates safety hazards in multiple industries, the phenomenon remains the main de-icing mechanism employed by the popular electro-thermal ice protection systems (ETIPS). To improve the technique's ice removal capability and minimize its energy consumption, an experimental and numerical investigation of ice shedding produced by ETIPS in de-icing configuration is presented in this paper. An experimental campaign conducted in the von Karman Institute's (VKI) icing wind tunnel (IWT) shows several ice detachment mechanisms. A one-dimensional phase change solver is developed and used to conduct complementary ice melting simulations. Coupled numerical and experimental results are used to determine the most important ice shedding parameters. Particularly, an ice shedding threshold value of the melted layer thickness produced at the heated surface-ice interface is observed.

Turbulent heat transfer is an extremely complex phe nomenon that has challenged turbulence modellers over various decades. In the recent past, several attempts have been made for the assessment and further development/calibration of t he available turbulent heat flux modelling approaches. One of the main hampering factors with respect to the further assessment of these modelling approaches is the lack of reference data, i.e. experimental or numerical via the use of Direct Numerical Simulations (DNS). Within the fram ework of the EU SESAME and MYRTE projects, an extensive and collaborative effort has been put forward to generate a wide range of reference data, both experimental and numerical, to fill this gap. In parallel, this data has been used to validate and/or improve the classical and s ophi ticated turbulent heat flux modelling approaches. This article reports the experimental and DNS datab ase that has been generated within these projects for various low-Prandtl flow configuration s in different flow regimes. This includes three experiments: confined and unconfined backward facing steps with low-Prandtl fluids, and a forced convection planar jet case with two differen t Prandtl fluids. In terms of numerical data, seven different flow configurations are considered: a wall-bounded mixed convection flow at low-Prandtl number with varying Richardson number ( Ri) values; a wall-bounded mixed convection flow in a bare rod bundle configuration f r two different Reynolds numbers; a forced convection in a confined backward facing step (BFS) for two different Prandtl fluids; a forced convection impinging jet for three different Prandt l fluids corresponding to two different Reynolds numbers of the fully developed planar turb ulent jet; a mixed-convection cold-hot-cold The 18 International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) Log Number: 000 Portland, Oregon, USA, August 18 22, 2019 triple jet configuration corresponding to Ri=0.25; an unconfined free shear layer for three different Prandtl fluids; and a forced convection i nfinite wire-wrapped fuel assembly. This wide range of reference data is used to evalua te, v lidate and/or further develop different turbulent heat flux modelling approaches, namely si mple gradient diffusion hypothesis based on constant and variable turbulent Prandtl number; exp licit and implicit algebraic heat flux models; and a second order turbulent heat flux model. Lastl y, this article will highlight the current challenges and perspectives of the available turbul ence models, in different codes, for the accurate prediction of flow and heat transfer in lo w-Prandtl fluids.

•Development of a modeling approach for simulating the thermal hydraulics of heavy liquid metal nuclear reactors.•Detailed description of the modeling of each component through the MYRRHA reactor.•Detailed analysis of the flow field of the MYRRHA reactor under operating condition.•Assessment of the thermal load on the structures as well as the thermal stratification in the upper and the lower plenum.

Liquid metal cooled reactors are envisaged to play an important role in the future of nuclear energy production because of their possibility to use natural resources efficiently and to reduce the volume and lifetime of nuclear waste. Sodium and Liquid lead (-alloys) are considered the short and long term solution respectively, as coolant in GEN-IV reactor. Thermal-hydraulics of liquid metals plays a key role in the design and safety assessments of these reactors. Therefore, this is the main topic of a large European collaborative program (the Horizon 2020 SESAME) sponsored by the European Commission. This paper will present the progress in the project with respect to liquid metal cooled reactor thermal-hydraulics (liquid metal heat transfer, fuel assembly thermal-hydraulics, pool thermal-hydraulics, and system thermal-hydraulics). New reference data, both experimental and high-fidelity numerical data is being generated. And finally, when considering the system scale, the purpose is to validate and improve system thermal-hydraulics models and codes, but also to further develop and validate multi-scale approaches under development.

The development of Gen IV nuclear reactors entails research oh heavy liquid metals, which are considered as appropriate coolant agents due to their high thermal conductivity and favorable nuclear safety characteristics. These fluids are characterized by a very low Prandtl number (between 0.006 and 0.025). During the design of such reactors, the scenarios of maintenance or loss-of-flow accidents consider a pure natural convection loop inside the reactor. The CFD modeling of the momentum and heat transfer must contemplate natural convection in low Prandtl number fluids, however in literature these flow configurations are not usual. This is why in the present article, Large Eddy Simulations over a natural convection boundary layer at Pr = 0.025 are presented and described. Turbulence is triggered by adding a perturbation in the boundary layer. The adopted numerical approach is validated through a Large Eddy Simulation at Pr = 0.71, where heat transfer, friction coefficient and mean and turbulent flow fields are compared with measurements in literature. Once turbulence is reached in the Pr = 0.025 boundary layer, flow characteristics as Nusselt number, skin friction coefficient and turbulent profiles are calculated and compared with the Pr = 0.71 simulation to assess the effect of Prandtl number on heat and momentum transfer.

The thermal-hydraulic challenges of a nuclear reactor are numerous and mastering them is crucial for the design and safety of new reactors. Numerical simulation through computational fluid dynamics (CFD) codes or system thermal-hydraulic 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 center dot CEN. It is a full plexiglass 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 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 nominal operating condition and a natural convection case simulating decay heat removal. 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.