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Transient flow characteristics and dissipation mechanism in pressurized pipeline were investigated based on 1D friction models and 3D turbulence models, where the pressure–density model was combined into the 3D continuity equation allowing for the elasticity of the fluid and the pipes. The applicability of 3D realizable k–ε and 3D SST (shear stress transport) k–ω turbulence models was verified with comparison to 1D traditional water hammer models and the experimental data for fast closing of the valve in the reservoir–pipe–valve system. The valve closure rule was instantaneously carried out using the grid slip CFD (computational fluid dynamics) technique. The SST k–ω turbulence model has the highest accuracy in predicting the pressure attenuation of transient flows. The 3D detailed flow field confirms that the asymmetric flows induced by the change of valve opening within approximately three-fourths of the pipe inner diameter before the valve are captured. In the pressure wave cycles, the unsteady inertia, axial pressure gradient, viscous shear stress and turbulent shear stress mainly influence the velocity variations. During the pressure wave propagation, the viscous and turbulent dissipation are critical in the pressure attenuation in the wall region; the viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation increases to the maximum values at y+ = 13–23. HIGHLIGHTS The 3D weakly compressible and dissipation mechanism models are introduced to investigate transient flow characteristics.; The asymmetric flows induced by the change of valve opening are captured well within approximately three-fourths of the pipe inner diameter before the valve.; The viscous dissipation is mainly concentrated in the viscous sublayer, while the turbulent dissipation has maximum influence at y+ = 13–23.

This study investigates using tailor-developed combustion and air-handling system concepts to achieve high-efficiency, clean gasoline compression ignition (GCI) combustion, aimed at addressing a future heavy-duty ultralow NOx standard of 0.027 g/kWh at the vehicle tailpipe and the tightening CO2 limits around the world by combining GCI with a cost-effective engine aftertreatment system. The development activities were conducted based on a 15 L heavy-duty diesel engine. By taking an analysis-led design approach, a first-generation (Gen1) GCI engine concept was developed and tested, encompassing tailor-designed piston bowl geometry, fuel spray pattern, and swirl motion paired with a customized, fixed-geometry, two-stage turbocharging system and a high-pressure EGR loop with two-stage cooling. Across four key steady-state operating points, the Gen1 GCI concept demonstrated 85–95% lower smoke and 2–3% better diesel-equivalent gross indicated fuel consumption compared to the diesel baseline at 1 g/kWh engine-out NOx. By upgrading to a Gen2 air-handling concept that was composed of a prototype, single-stage, variable-geometry turbocharger and a less restrictive EGR loop, 1D system-level analysis predicted that the pumping mean effective pressure was reduced by 43–54% and the diesel-equivalent brake-specific fuel consumption was improved by 2–4%, thereby demonstrating the performance enhancement potential of refining the air-handling system.

Unlined pressure tunnels in sound rock, combined with pressurized sand traps at the downstream end, allow for low-cost construction of hydropower tunnel systems. This design concept is utilized in hydropower plants across the world. Currently, many such power plants are being upgraded with higher installed capacity, which may result in challenges with the sand trap efficiency. A physical scale model test, accompanied by 3D CFD simulations of a case study pressurized sand trap, has been studied for economic retrofitting. The geometric model scale is 1:36.67 while the velocity scale and sediment scale are 1:1 (same average flow velocity and sediment size in model and prototype). This is currently an uncommon scaling approach but with several advantages, as presented in this paper. Various options for retrofitting were investigated. A combined structure of ramp and ribs was found to significantly improve the sediment trap efficiency. The main novelties from this work are the proposed design of the combined ramp and rib structure. Secondary results include an efficient setup for physical scale models of pressurized sand traps and a methodology that combines the benefits of 3D CFD simulations with physical scale models testing for sand trap engineering and design.

Increasing power densities of electric machines in e-vehicles in addition to the resulting quest for enhanced cooling concepts are bringing forward the importance of defining adequate heat transfer correlations in air gaps. This is a highly challenging topic, as there exist no generally applicable flow and heat transfer phenomena descriptions for air gaps due to their highly variable geometrical properties and operating conditions. As an answer to this challenge, this paper presents a workflow that defines an adequate 3D CFD model for an arbitrary air-gap design that includes its system-dependent boundary conditions. The workflow is built on the recognition of underlying air-gap flow phenomena, which are used to steer the subsequent design of the 3D CFD model in a systematic step-by-step manner. Consequently, the complexity of the 3D CFD model gradually increases to the point where it provides an adequate flow and heat transfer description. Validation of the workflow is presented for a wide range of air-gap designs and flow conditions. It is demonstrated that the 3D CFD models obtained with the workflow match the experimentally obtained data from various flow cases that have been documented in the literature. Considerable optimization of computational costs, offering potentially an order-of-magnitude reduction in computational time, is achieved as a result of computational domain span optimization and transient simulations being applied only when required. The validation confirms that this workflow facilitates construction of valid 3D CFD models without the prior knowledge of flow and heat transfer phenomena in a specific air gap. This workflow thus provides a reliable and computationally efficient tool for valorization of convective heat transfer, and opens up prospects for time- and cost-efficient optimizations of electric machines’ cooling system designs.

PhD (Nuclear Engineering), North-West University, Potchefstroom Campus The fourth-generation nuclear reactors have many safety features, including the reactor cavity cooling system (RCCS). This system is intended to remove decay heat from the reactor cavity. Designs exist for both air-cooled and water-cooled configurations. It operates completely passively and is designed to operate without external inputs. The accurate simulation of the phenomena in a reactor cavity cooling system is important for design calculations, to ensure reactor designs that are passively safe. The codes that are used to simulate the phenomena must therefore be verified and validated. One method to validate both a particular design and simulation code is to build an experimental facility based on a prototype. In many cases scale models are constructed of prototype designs. The facility constructed at the University of Wisconsin (Madison) is an example of a scale model of an RCCS. The facility represents a 5° radial slice of the RCCS of the modular high temperature gas-cooled reactor (MHTGR) design. The prime focus of the study is the heated section/heater box of the facility. A study was done by Lisowski (2013) which encompassed single and two-phase experiments as well as a simplified version that was numerically simulated. This study aims to expand on the single-phase simulations done by Lisowski, by making fewer geometry simplifications. The study focussed on simulating the heated section of the UW RCCS facility by using 3D computational fluid dynamics (CFD) and simulating the full loop by using 1D system CFD. The 3D simulations explored different geometric configurations, namely circular riser tubes with and without fins, square tubes with and without fins and rectangular tubes with and without fins. The heat fluxes and temperatures on the surfaces were examined and compared between the different geometry configurations. The 3D CFD code was also coupled with a 1D systems CFD code. The systems were coupled such that the 1D and 3D code would transfer boundary conditions. The codes were linked such that each respective code’s strength could be exploited for the best combination of accuracy and effective use of the computational resources. Two variations were simulated and similarly to the 3D cases, the heat fluxes and temperatures on the various surfaces were examined for comparison. The limitations of the study mean that the results can’t be used as a direct comparison with the experiments but can nonetheless be used to philosophically understand the phenomena that occur within the facility. The finned configurations shielded the back wall from direct radiation heat transfer from the heater wall, which is preferable in terms of preserving the structural integrity of the reactor cavity wall. The cases without fins resulted in higher temperatures on the back walls, but more uniform temperature distributions around the circumference of the riser tubes. This in turn resulted in lower stresses due to uniform thermal expansion. Radiation heat transfer was the dominating mechanism, but the convection heat transfer nonetheless contributed a non-negligible fraction of the heat transfer. The convection heat transfer coefficients were calculated on the surfaces in the air-filled cavity and for the inner surfaces of the water-cooled riser tubes. Two variations of the coupled methodology were tested, and the wall temperatures compared well between the coupled methods as well as with the 3D method. The convection heat transfer coefficients were also compared for the inner surfaces of the middle riser tube for the three approaches. The coefficients compared reasonably well in terms of the trends that were exhibited by the different approaches on the four inside surfaces. Doctoral

While striving for a circular economy of metals, the Flash Smelting Furnace (FSF) is the most common and “green” aggregate for primary smelting of copper concentrates, because of already today low CO2-emissions compared to other smelting technologies. High dust carry-over often leads to problems with flue dust accretions in its subsequent cooling aggregate, the Waste Heat Boiler (WHB). Removing these accretions causes mechanical stress for the boiler tubes and can lead to extended downtime and maintenance. The WHB has a limited accessibility towards experimental studies because of its harsh process conditions. Hence, Computational Fluid Dynamics (CFD) models appear as convenient option for WHB studies and design, but are not used for the evaluation of flue dust accretions yet. For the inclusion of this feature into a three-dimensional CFD model of the entire WHB, a new sticking function is developed. It is based on the industrial experience that flue dust is only sticky above a certain softening temperature. Since the WHB has a varying dust input due to the flexible operation of the FSF, a parameter study is conducted for standard flue dust, pure copper oxide dust and pure iron oxide dust, finding minor sensitivity towards the flue dust density and no sensitivity towards the dust heat capacity. From these findings, recommendations for the minimization of flue dust accretion formation in the WHB are derived.

Alteration of the flow characteristics in coronary vessels is correlated with coronary heart disease (CHD). In particular, wall shear stress (WSS) appears to be a hemody-namic key factor in the genesis of CHD. Since computational fluid dynamics (CFD) is a well-known method for the inves-tigation of WSS, it may be a valuable tool for the prediction of CHD. Latest imaging techniques, such as optical coher-ence tomography (OCT) in conjunction with angiography deliver precise 2D data sets of patient-specific vessel geome-try, which can be used for CFD analysis. Current CFD stud-ies utilize patient-specific geometries, but are lacking well defined physiologic inflow conditions. In this study, we present an inflow mapping method for patient-specific arterial vessels, which is capable of consider-ing the influence of bifurcations located proximal of the OCT-data set. At first, the patient-specific vessel was recon-structed. For this purpose the OCT-based vessel cross sec-tions were arranged along an angiographic based vessel pathway. Secondly, we simulated the flow field in a generic bifurcation model by means of CFD. Thereafter the flow field of a side branch was extracted and transferred (mapped) to the inlet of the patient-specific vessel. To evaluate the influence of the physiological inlet the WSS distribution of the same patient-specific vessel was calculated using an axial-symmetric inflow condition. Analy-sis of the simulation data yielded deviations of the WSS distribution in the proximal vessel segment. A bifurcation, located upstream of the relevant vessel segment strongly affects the flow in the OCT-based vessel reconstruction and has a strong influence on the results of the numerical analy-sis. Therefore, it is important to implement not only the pa-tient-specific geometry, but also an inlet boundary condition adapted to the upstream velocity distribution reflecting the actual proximal flow situation of the vessel.

The aerodynamic design of turbomachinery is an exciting engineering problem that involves a vast design space and requires proficiency in multiple engineering disciplines. For multi-stage compressors, the large dimension of the design space arises from the geometric freedom to shape each blade row individually. Although the basis of most designs is formed by throughflow computations, the state-of-the art for aerodynamic evaluation is steady-state RANS. The computational expense for a single evaluation of a multi-stage machine with RANS is affordable, shape optimizations with hundreds of evaluations becomes expensive. This paper presents two strategies to tackle these problems: Firstly, a novel airfoil family is employed that helps to reduce the number of design parameters. It was generated based on a parametric study of optimal airfoil shape for varying design requirements. Secondly, an optimizer is used that supports simultaneous evaluations of the objective function on multiple fidelity levels. Here, cheap throughflow calculations are conducted on the low-fidelity side and RANS is used on the high-fidelity side. Inside the optimizer, multi-fidelity support is enabled by a Co-Kriging surrogate model. This approach is expected to speed-up the optimization by guiding expensive evaluations of the 3D CFD setup into promising regions of the design space. These strategies are assessed by testing different optimization setups for a four stage compressor. Both purely low and high-fidelity optimizations are conducted as well as multi-fidelity optimizations. In comparison to the baseline design, the isentropic efficiency predicted by RANS for the working line points on the 95% and the 100% speed line is increased by above 1.2%. The driving mechanism is a load redistribution between the stages that mainly reduces the shock strength of the second rotor.

International audience; In this paper, reactive unsteady three-dimensional numerical simulations of a chemical looping combustion (CLC) unit are presented. The configuration is a 120-kW pilot plant working with perovskite, CaMn0.9Mg0.1O3d, as the selected oxygen carrier. Numerical simulations were performed using NEPTUNE_CFD code in the frame of an Euler-Euler approach by computing both gas and solid phases in an Eulerian technique, accounting for specific closures in order to model the interphase mass, and momentum and energy transfers. Heterogeneous reduction and oxidation (gas–solid) reactions were modeled by means of a grain model to account for the competing mechanisms of the chemical reaction onto the grain surface, the gaseous diffusion through the product layer around the grain, and the external transfer through the gas mixture surrounding the particle. Results from numerical simulations were assessed against experimental measurements and analyzed in order to acquire insight on the local behavior of reactive gas-particle flow in the CLC system. The theoretical/numerical tool developed in this work can be used for the design upgrade of crucial parts of the system in the stage of scaling-up from pilot to industrial plants.

Coronary diseases are the main reason for death in the western world. Bio-fluid mechanical correlations with arterial diseases are in the focus of our research. To treat occluded vessels, stents are implanted. Stent implantations can be associated with blood flow disruptions leading to restenosis or thrombosis formation. Numerical flow simulation is a promising tool to evaluate the hemodynamic performance of cardiovascular implants, but is resource-intensive in time and computational power. Therefore, a reduction in grid size would be beneficial due to economic exploitation of computational cost. The purpose of this numerical investigation is to substitute the computational domain of a distal stented bifurcation with a stented straight vessel by using the right inlet condition. The deviation of the results of the two different methods to simulate the blood flow situation in a bifurcation is marginal. This inlet can be used for standardised simulations of bifurcations were lesions commonly occur.

Simple design and low power coefficient of Savonius-style wind turbines make them attractive in experimental and computational fluid dynamics (CFD) based optimization studies. Still, after numerous studies the power coefficient is low, and the single optimal Savonius-style wind turbine shape and configuration is not known. This leaves room for improving the power coefficient, and the objective of this paper is to find an improved solution with application of smart numerical optimization. Several Savonius blade improvements proposed by other researchers were initially analyzed. The numerical (3D CFD) analysis has shown that simple modifications of the blades can be better than more complicated shapes such as spline or elliptical curve. This has encouraged the investigation on what is the limit to the optimized design which used only simple circular-arc based blades. Thus, we perform a global optimization of Savonius blade pair where each pair is composed of two circular arc segments. The smart numerical optimization was performed using 2D CFD and the results were verified and compared with the previous designs using the 3D CFD. The selected optimization operating conditions were tip speed ratio 0.9 and wind speed 12 m/s. The novel optimized design achieved 39% improvement of the maximum power coefficient relative to the classical Savonius design.

In the present paper, three-dimensional Fluid structures and wake characteristics are evaluated for a square cylinder with an upstream splitter plate. The splitter plate divides the incoming flow in two streams, the upper and lower one, existing between them a velocity ratio. Two different Reynolds numbers of 56 and 200 and three different velocity ratios are here considered. The effect of the mixing enhancement using a square cylinder located downstream of the splitter plate is evaluated. A Floquet analysis to compute the spanwise wavelengths of three dimensional disturbances appearing in the square cylinder wake with and without a splitter plate is performed. It is observed that the use of the detached splitter plate has a stabilizing effect at low velocity ratios. However, when the velocity ratio increases, the vortex shedding suffers a linear increase and the wake resembles that of a mixing layer. Vortex dislocations appear at ratios larger than 2, which points out the onset of a bifurcation to a more chaotic wake. The wavelength of this secondary instability has been measured by means of Floquet analysis and two-point correlations being in the order of 3.5D.

A numerical study has been carried out to investigate heat transfer enhancing flow field in 28 geometrically different sinusoidally, spirally corrugated tubes. To vary the corrugation, the height of corrugation e / D and the length between two successive corrugated sections p / D are varied in the ranges 0–0.16 and 0–2.0 respectively. The 3D Unsteady Reynolds-averaged Navier–Stokes (URANS) equations combined with the transition SST turbulence model are solved using the finite volume method to obtain the fully-developed flow field in a repeatable section of the heat exchangers at a constant wall temperature and at Re = 10 , 000 . By studying the wide range of geometrically different tubes, the flow conditions vary significantly. At low corrugation heights, only a weak secondary flow centred in the corrugated section is present. At higher corrugations heights, the tangential velocity component increases and eventually exceeds the axial velocity component causing the highest pressure to be located at the centre of the corrugated section. At these high corrugation heights, a further increase in corrugation height will at best only result in a small increase in Nusselt number but at a significantly higher pressure loss. To assess the performance as a heat exchanger, the ratio of enhanced Nusselt number to enhanced friction factor η = ( Nu / Nu s ) / ( f / f s ) 1 / 3 compared to the non-corrugated tube is used. Using this parameter, the simulations show a decrease in performance at higher corrugation heights. To link the detailed flow fields to the performance as a heat exchanger, non-dimensional correlations for heat transfer, pressure loss, and performance parameter are given.

A simplified model for predicting the overall thermal performance of finned-tube heat exchangers considering water and air as hot and cold fluids, respectively, is investigated. The model is based on the classical epsilon-NTU method and the thermal convective resistance in each fluid is estimated after conventional type (Nusselt number) empirical correlations. The model is calibrated with catalogue data of a heating coil. Calibrations of six families of model versions are performed by using different numbers of operating cases ranging from 2 to 320, some of them taking into account the influence of varying properties. The calibrated versions are tested for operating cases listed in the catalogue and the best performing versions are identified, such as the one calibrated with 24 cases and taking into account the effect of the fluid properties, which provided better accuracy than the versions calibrated in previous works. A test of the method robustness is conducted regarding the influence of the initial guessed values of the thermal resistances on the calibration procedure. The validity of the component model is further investigated by using a set of published experimental data for an automotive radiator covering ranges of practical interest of the mass flow rates of both air and water streams, and some versions providing excellent results are identified. The model based on a suitable version previously calibrated and tested is a promising procedure for the modular component simulation of finned-tube heat exchangers, when used as air conditioning heating coils or in other particular applications. (C) 2016 Elsevier Ltd. All rights reserved.

The off design behavior of a 100kW Turbec T100P micro gas turbine fuelled with methane is analyzed in the paper. The work is focused on the analysis of combustion efficiency, overall performance and gaseous emissions at different loads. A critical comparison between experimental data and results of a 3D CFD analysis of the combustor is discussed. The RANS RSM turbulence model is used in the numerical computations. The Zeldovich mechanism for NO formation evaluation is coupled to a methane-oxygen multistep chemical kinetic mechanism for predicting the concentration of O2, CO2, CO and NO at the exhaust. The experimental campaign showed no sensible variations in NOxemissions by varying MGT load; otherwise a great CO increasing is highlighted by load decreasing. The results of numerical analysis are in good agreement with experimental data as concerns CO emissions, while overestimate NO production in the diffusive flame region at 50% load.

[EN] The aim of this paper is to identify and investigate the potential and limitations of diesel-gas combustion concepts for high speed large engines operated in gas mode with very small amounts of pilot fuel (, The authors would like to acknowledge the financial support of the COMET Competence Centres for Excellent Technologies Programme of the Austrian Federal Ministry for Transport, Innovation and Technology (BMVIT); the Austrian Federal Ministry of Science, Research and Economy (BMWFW); and the Provinces of Styria, Tyrol, and Vienna for the K1-Centre LEC EvoLET. The COMET Programme is managed by the Austrian Research Promotion Agency (FFG). Austrian Research Promotion Agency (FFG) (844604).

International audience; The aim of this article is to study a hydrodynamic separator equipped with a separation screen. The main purpose of this separator is to capture macro-wastes in order to prevent their release into the environment. The methodology consists in visualizing how the separator hydraulically works using laboratory experiments based on a physical model, 3D numerical modeling and the study of an operating hydraulic separator. The 3D numerical modeling enabled to predict the flow within an operating separator (Trouville-sur-Mer). The hydrodynamic behaviour has been studied following different cases : flow range varying between 100 and 300 L/s, operating of the security overflow, etc. The instrumentation of the operating separator confirmed the results predicted by the numerical modeling. Finally, maintenance and operating costs have also been approached.; Dans cet article, nous relatons l’étude d’un séparateur hydrodynamique muni d’une grille séparative. L’objectif principal du séparateur est de capturer les macrodéchets afin d’éviter leurs rejets dans le milieu naturel. La méthodologie employée consiste à déterminer le fonctionnement hydraulique de l’ouvrage en utilisant l’expérimentation en laboratoire sur un modèle physique, la modélisation numérique 3D puis l’étude d’un ouvrage en fonctionnement. La simulation numérique 3D a permis de prédire l’écoulement au sein d’un ouvrage de terrain (Trouville-sur-Mer). Le comportement hydrodynamique a pu être étudié suivant différents cas : plage de débit variant de 100 à 300 L/s, fonctionnement de la surverse de sécurité… L’instrumentation du site a permis de conforter les résultats prédits par la modélisation. Enfin, la maintenance et les coûts d’exploitation de tels ouvrages sont également abordés.

The performance of a micro gas turbine in terms of global efficiency and exhaust emissions at different loads and methane-hydrogen blends has been experimentally studied. The load was varied from full load down to half load. A critical comparison between experimental data and results of the 3D CFD analysis of the combustor is discussed in order to study the effects of part load operation. Additional objective of the present study is to extend the numerical analysis of the combustor in order to describe the influence of a wider range of hydrogen concentrations in the fuel gas mixture. Numerical simulations were performed through the commercial code ANSYS CFX 14.5. Turbulence model adopted was the RSM RANS model, which ensures a good evaluation of effects of swirled turbulent flows in the combustion chamber. The oxidation of methane is simulated by using multistep kinetics models. They assure a better reproduction of CO emissions with load. Boundary and initial conditions were defined by using experimental data, when available, and results of numerical matching analysis, which assumes importance in case of absence of specific measurements at combustor inlet. Discussion of results is mainly focused on the variation in terms of exhaust gaseous emissions and temperature distributions in the combustor by varying load and fuel. A numerical evaluation of the MGT combustor behavior in critical conditions is also presented.Copyright © 2014 by ASME

The main target of nowadays engine designers is to focus on exhaust emissions, fuel consumption and engine performance, so during the design phase of a new internal combustion engine, all the aspects related to friction and mechanical power loss must be deeply considered. And then, also the friction related to engine lubrication system must be analyzed and studied. In this paper a tridimensional CFD analysis of the lubrication circuit oil pump of a modern high-performance engine manufactured by Aprilia will be shown. The model was build up with PumpLinx®, a commercial CFD 3D code by Simerics Inc.®, taking into account all the phenomena associated to the fluid cavitation. The model was validated by data of an experimental campaign performed on a hydraulic test bench, at the Industrial Engineering Department of the University of Naples, Federico II.

The automotive manufacturers are nowadays more and more interested in crosswind aerodynamics. Indeed, the driver is subjected every day to strong side air flows, for example when overtaking another vehicle or when passing through a lateral wind wall, generated by terrain topography (as in the case of the passage near the empty space between two buildings).The aerodynamic efforts generated in these situations can lead to undesired lateral deviations,which can be dramatic if the driver is surprised. Different experimental studies, reproducing the effects of a dynamic yaw angle, pointed out the issues of the steady methods, commonly used to qualify the vehicle crosswind behaviour. Little is still known about the physics behind these unsteady phenomena. This is the main topic of this work, by studying the aerodynamics of a fixed vehicle subjected to both a longitudinal flow and a side wind gust. The goal is the identification of the near-vehicle vortex structures, by means of PIV measurements and CFD calculations, and their correlation with the evolution of the efforts. An agreement between the ISAT, a department of the University of Burgundy, and the ISAE of Toulouse, permitted to carry out this research with the resources of the latter laboratory. The work focuses on the use of the “rafale latérale” (side gust) test bench, made up with a main wind tunnel connected with an auxiliary one by means of a shutter system,whose opening is held by a “Mexican Wave” law. This approach is inspired by the work of Dominy and Ryan (2000). The experimental analysis was carried out by means of Time-Resolved and stereoscopic PIV, and by a five components unsteady balance as well. Anidentical test bench was numerically reproduced with the 3D CFD software FLUENT©.Moreover, an additional 2D CFD model, based on the meshless method, has been developed for future studies. This kind of approximation method has been chosen for its robustness innon-continuous problems and because of its adaptability when moving boundaries are needed.The first phase of this work consisted on wind tunnels set-up, both for the real test bench and for the CFD model. The yaw angle field is homogeneous, 21° in the measurement region. The yaw angle evolution, at given point, respects the step wise behaviour, imposed by the gust passage. As far as the efforts are concerned, two versions of the Windsor body car model were studied, that is a squareback geometry, generating, for longitudinal flows, 2D wakestructures, and a fastback geometry (rear window inclined by 25°), producing cone-liketrailing vortices. Force overshoots were seen after the gust arrival, as seen in literature. In particular, the yaw moment coefficient overshoots are 29% and 19% higher than the steady yaw angle tests, for the squareback and the fastback geometries, respectively. If the side forceis concerned, the entities of these overshoots are 10% and 14%, respectively. Our testspointed out that efforts establish after the vehicle has driven 5.5 times its length in thecrosswind. In order to explain the different behaviour of the two geometries, it is discussed about the unsteady evolution of the vortices called, in this report, ΓA, ΓB, ΓC et Γ1. A strong correlation between the side efforts and the circulation of the most energetic vortex, ΓA,having its origin in the front leeward side of the vehicle. The ΓA vortex is so the best index for the study of the crosswind unsteady phenomena. The coupled analysis between vortex structures and efforts confirmed the presence of a higher side force for the squareback geometry. The inverted effect has been observed for the yaw moment, L’aérodynamique latérale des véhicules automobiles suscite de nos jours de plus en plus d’intérêt de la part des constructeurs. L’automobiliste est en effet soumis quotidiennement à de forts courants d’air latéraux, que ce soit lors du dépassement d’un autre véhicule, ou alorsen passant dans un couloir de vent du à la topographie du terrain (passage devant un espace entre deux immeubles par exemple). Les efforts aérodynamiques mis en jeu dans ces situations peuvent provoquer des mouvements non désirés du véhicule, pouvant avoir des conséquences dramatiques si le conducteur se laisse surprendre. Des études expérimentales reproduisant les effets d’un dérapage dynamique ont mis en évidence des phénomènes transitoires importants mettant à défaut les modèles stationnaires généralement pratiqués par les constructeurs pour qualifier le comportement de leurs véhicules en présence de dérapage. Les mécanismes responsables de ces phénomènes transitoires sont encore mal connus de la communauté scientifique. Ce travail propose d’approfondir ce sujet au travers de l’étude de l’aérodynamique d’un véhicule terrestre fixe soumis à un vent longitudinal et à une rafale de vent latéral. Le but principal est d’identifier les structures tourbillonnaires au moyen de mesures PIV et de calculs numériques des champs de vitesse autour d’une maquette automobile et de les corréler aux efforts aérodynamiques. Un accord entre l’ISAT, composante de l’Université de Bourgogne, et l’Institut Supérieurde l’Aéronautique et de l’Espace (ISAE) de Toulouse a permis de mener l’étude avec les ressources de cet établissement. Le moyen d’essai principal, créé par l’ISAE, est le banc« rafale latérale », constitué d’une soufflerie principale et d’une soufflerie secondaire, dont la sortie à volet déferlants (« Mexican Wave ») est inspirée de l’approche proposée par Ryan et Dominy (2000). L’analyse expérimentale a été effectuée à l’aide de la PIV résolue en temps et stéréoscopique, et d’une balance dard instationnaire à cinq composantes. Un banc« numérique » identique a été constitué à l’aide du logiciel FLUENT©, pour des calculs 3D. De plus, un modèle 2D annexe, basé sur la méthode « meshless », a été développé pour de futures investigations, en raison de sa robustesse pour des problèmes à fortes discontinuités et sa bonne adaptabilité aux problèmes avec frontières mobiles.Une première phase de ce travail a consisté en la mise au point des bancs expérimental et numérique, avec génération d’un champ de dérapage homogène, de 21° dans la zone de mesure. L’évolution du dérapage en chaque point respecte bien la forme d’un créneau imposé par la rafale. Pour l’analyse des efforts, deux géométries de maquette ont été étudiées, à savoir un corps de Windsor à culot droit générant, pour un écoulement longitudinal, des structures de sillage bidimensionnelles, et son homologue à culot incliné de 25°, générant des tourbillons « cigare ». Des pics d’efforts ont été observés à l’arrivée de la rafale, tout comme la littérature le prédit. Pour ce qui est du coefficient du moment de lacet, les sursauts sont de 29 % et 19 % respectivement pour la maquette à culot droit et celle à culot incliné, par rapport aux valeurs stationnaires. Concernant le coefficient de force de dérive, ils sont de 10 % et 14 %, respectivement. Lors de nos essais, ces efforts se sont établis après 5.5 longueurs de maquette. Afin d’expliquer la différence de comportement entre les deux maquettes en termes d’efforts, l’évolution temporelle des tourbillons nommés, dans ce mémoire, ΓA, ΓB, ΓC et Γ1 à été discutée. Il en est ressorti une forte corrélation entre la circulation du tourbillon ΓA, le plusénergétique, naissant à l’avant du flanc sous le vent de la maquette, et les efforts latéraux, de sorte que ce tourbillon serait le meilleur témoin des phénomènes instationnaires mis en jeu dans l’étude de l’effet du vent latéral. [...]

A mathematical modeling approach for the study of a directional valve is proposed in this paper. The analyzed valve is a High flow 6-way directional valve, with nominal flow-rate of 2500 l/min and maximum inlet pressure of 26 bar that is used for safety shut down for Power Plants. The final goal is to obtain the best energy efficiency of the valve, request by this specific application. The study is addressed to the design optimization of hydraulic components using a simulation methodology. The analysis has been performed through a three-dimensional CFD modeling technique by using the commercial code PumpLinx®, developed by Simerics®. This approach allows the study also of particular applications, like the valve analyzed, where the experimentation is complex and expensive with a high reduction of the component’s development phase. This paper is the first part of a research focused on the core design optimization by using a 3D CFD simulation methodology. With the modeling technique, the flow behavior has been deeply studied by visualizing the pressure, the velocity and the kinetic energy on several valve’s sections. A model for the turbulence has been implemented in the simulation. Several new designs of the valve core have been modeled and the final geometry has achieved the goal of this first part of the study.

The aim if this paper is the analysis of a lubrication circuit adopting two simulation models to study the influence of three different lubrication oils. First, the oils pump performance were analyzed with a tri-dimensional simulation model, realized with the commercial code PumpLinx ® , which allowed to obtain the performance curves of the oil pump, varying the oils. Then the lubrication circuit was studied with a 1D model, realized with the commercial code LMS AMESim ® , and the behaviour of the lubrication circuit was analyzed in terms of pressure drops and components oil consumption. The adopted oils were: 0W30; 5W40 and10W60. In previous activities, both models showed good correlation with experimental data. Analyzing the models results, it was noted that the pressure behavior in the lubrication circuit is highly influenced by the oil, especially for low engine speed and high temperatures. The adopted methodology, that couples mono-dimensional and tri-dimensional models, allowed to analyze the oil influence in a lubrication circuit, avoiding excessive computational cost, but with an acceptable accuracy