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Viewing 1 to 30 of 95
Technical Paper
2014-10-13
Harun Mohamed Ismail, Hoon Kiat Ng, Suyin Gan, Tommaso Lucchini
Modelling the combustion process of a diesel-biodiesel fuel spray in a 3-dimensional (3D) computational fluid dynamics (CFD) domain remains challenging and time-consuming despite the recent advancement in computing technologies. Accurate representation of the in-cylinder processes is key to the success of CFD studies as they are able to provide invaluable insights into these events, which are limited when using conventional experimental approaches. This is especially true for emerging new fuels such as biodiesels as the fundamental understanding of these fuels under combusting environment is still limited. The reported work here is dedicated to evaluating the Adaptive Local Mesh Refinement (ALMR) approach in OpenFOAM® for accurate simulation of reacting biodiesel-diesel fuel spray. An in-house model for thermo-physical and transport properties is integrated to the code, along with a chemical mechanism comprising 113 species and 399 reactions. Simulation results are compared against data from Chalmers High-Pressure-High-Temperature Constant-Volume Combustion Chamber (HPHT-CVCC) experimental test-bed studies in terms of liquid-droplet penetration length, vapour penetration length and spray temporal distribution.
Technical Paper
2014-04-01
Robert Golimbioschi, Giampiero Mastinu, Luca Cordioli, Massimiliano Gobbi, Davide Tagliabue, Giorgio Previati, Francesco Braga
Abstract A new electric powertrain and axle for light/medium trucks is presented. The indoor testing and the simulation of the dynamic behavior are performed. The powertrain and axle has been produced by Streparava and tested at the Laboratory for the Safety of Transport of the Politecnico di Milano. The tests were aimed at defining the multi-physics perfomance of the powertrain and axle (efficiency, acceleration and braking, temperature and NVH). The whole system for indoor tests was composed by the powertrain and axle (electric motor, driveline, suspensions, wheels) and by the test rig (drums, driveline and electric motor). The (driving) axle was positioned on a couple of drums, and the drums provided the proper torques to the wheels to reproduce acceleration and braking. Additionally a cleat fixed on one drum excited the vibration of the suspensions and allowed assessing NVH performance. The simulations were based on a special co-simulation between 1D-AMESIM and VIRTUAL.LAB. The contact between the wheels and the drums of the test rig were simulated by means of VIRTUAL.LAB.
Technical Paper
2014-04-01
Isabel Ramirez Ruiz, F. Cheli
Abstract In the last years the number of electronic controllers of vehicle dynamics applied to chassis components has increased dramatically. They use lookup table of the primary order vehicle global parameters as yaw rate, lateral acceleration, steering angle, car velocity, that define the ideal behavior of the vehicle. They are usually based on PID controllers which compare the actual behavior of every measured real vehicle data to the desired behavior, from look up table. The controller attempts to keep the measured quantities the same as the tabled quantities by using ESP, TC (brakes and throttle), CDC (control shocks absorbers), EDIFF(active differential) and 4WS (rear wheels active toe). The performances of these controls are good but not perfect. The improvement can be achieved by replacement of the lookup tables with a fast vehicle model running in parallel to the real vehicle. This model will allow to anticipate the vehicle reactions to driver maneuvers or the effect of road conditions, and will simplify the regulations of the controller making hopefully them more smoother (feed forward control).
Technical Paper
2014-04-01
Gianluca Montenegro, Augusto Della Torre, Angelo Onorati, Dalia Broggi, Gerd Schlager, Christian Benatzky
Abstract This work proposes a focus on the simulation of a rotative volumetric expander via a CFD code. A customized application of OpenFOAM® has been developed to handle the particular motion of the calculation grid. The model uses a mesh to mesh interpolation technique, switching from a calculation grid to the new one on the basis of mesh quality considerations performed on the fly. This particular approach allows to account for the presence of leakages occurring between the stator and blade tips and also occurring at the top and bottom of the vanes. The fluid considered is the refrigerant R245fa, whose particular properties have been determined resorting to the NIST database. Experimental data, measured at different conditions of mass flow and fluid temperature, are compared to calculation results. Moreover, the CFD analysis has allowed the estimation of the influence of the leakage mass flow occurring at the tip of the vanes on the overall machine performances.
Technical Paper
2014-04-01
Edoardo Sabbioni, Federico Cheli, Matteo Riva, Andrea Zorzutti
Abstract For passenger cars, individual tyre model parameters, used in vehicle models able to simulate vehicle handling behavior, are traditionally derived from expensive component indoor laboratory tests as a result of an identification procedure minimizing the error with respect to force and slip measurements. Indoor experiments on agricultural tyres are instead more challenging and thus generally not performed due to tyre size and applied forces. However, the knowledge of their handling characteristics is becoming more and more important since in the next few years, all agricultural vehicles are expected to run on ordinary asphalt roads at a speed of 80km/h. The present paper presents a methodology to identify agricultural tyres' handling characteristics based only on the measurements carried out on board vehicle (vehicle sideslip angle, yaw rate, lateral acceleration, speed and steer angle) during standard handling maneuvers (step-steers, J-turns, etc.), instead than during indoor tests.
Technical Paper
2014-04-01
Andrea Montorfano, Federico Piscaglia, Angelo Onorati
Abstract The dynamics and evolution of turbulent structures inside an engine-like geometry are investigated by means of Large Eddy Simulation. A simplified configuration consisting of a flat-top cylinder head with a fixed, axis-centered valve and low-speed piston has been simulated by the finite volume CFD code OpenFOAM®; the standard version of the software has been extended to include the compressible WALE subgrid-scale model, models for the generation of synthetic turbulence, some improvements to the mesh motion strategy and algorithms for LES data post-processing. In order to study both the initial transient and the quasi- steady operating conditions, ten complete engine cycles have been simulated. Phase and spatial averages have been performed over cycles three to ten in order to extract first and second moment of velocity; these quantities have then been used to validate the numerical procedure by comparison against experimental data. Complex unsteady features of turbulent fields like laminar-to-turbulent transition and tumble vortexes evolution have been studied either by time-resolved analysis and Proper Orthogonal Decomposition (POD).
Technical Paper
2014-04-01
Donald Selmanaj, Harald Waschl, Michael Schinnerl, Sergio Savaresi, Luigi del Re
Abstract Especially in view of more and more stringent emission legislation in passenger cars it is required to reduce the amount of pollutants. In the case of Diesel engines mainly NOx and PM are emitted during engine operation. The main influence factors for these pollutants are the in-cylinder oxygen concentration and the injected fuel amount. Typically the engine control task can be divided into two separate main parts, the fuel and the air system. Commonly air system control, consisting of a turbocharger and exhaust gas recirculation control, is used to provide the required amount of oxygen and address the emission targets, whereas the fuel is used to provide the desired torque. Especially in transient maneuvers the different time scales of both systems can lead to emission peaks which are not desired. Against this background in this work instead of the common way to address the air system, the fuel system is considered to reduce emission peaks during transients. The idea is to start from a base calibration and adapt the injection parameters, like start and amount of pilot and main injection, to reduce transient emission peaks.
Technical Paper
2014-04-01
Tommaso Lucchini, Marco Fiocco, Roberto Torelli, Gianluca D'Errico
The definition of a robust methodology to perform a full-cycle CFD simulation of IC engines requires as first step the availability of a reliable grid generation tool, which does not only have to guarantee a high quality mesh but also has to prove to be efficient in terms of required time. In this work the authors discuss a novel approach entirely based on the OpenFOAM technology, in which the available 3D grid generator was employed to automatically create meshes containing hexahedra and split-hexahedra from triangulated surface geometries in Stereolithography (STL) format. The possibility to introduce local refinements and boundary layers makes this tool suitable for IC engine simulations. Grids are sequentially generated at target crank angles which are automatically determined depending on user specified settings such as maximum mesh validity interval and quality parameters like non-orthogonality, skewness and aspect ratio. This ensures high quality grids for the entire cycle and requires a very reduced amount of user time.
Technical Paper
2014-04-01
Federico Brusiani, Gian Marco Bianchi, Stefania Falfari, Angelo Onorati, Tommaso Lucchini, Rita Di Gioia
Abstract Today, multi-hole Diesel injectors can be mainly characterized by three different nozzle hole shapes: cylindrical, k-hole, and ks-hole. The nozzle hole layout plays a direct influence on the injector internal flow field characteristics and, in particular, on the cavitation and turbulence evolution over the hole length. In turn, the changes on the injector internal flow correlated to the nozzle shape produce immediate effects on the emerging spray. In the present paper, the fluid dynamic performance of three different Diesel nozzle hole shapes are evaluated: cylindrical, k-hole, and ks-hole. The ks-hole geometry was experimentally characterized in order to find out its real internal shape. First, the three nozzle shapes were studied by a fully transient CFD multiphase simulation to understand their differences in the internal flow field evolutions. In detail, the attention was focused on the turbulence and cavitation levels at hole exit. The adopted simulation strategy was previously validated against experimental data.
Technical Paper
2014-04-01
Tommaso Lucchini, Gianluca D'Errico, Francesco Contino, Mehdi Jangi
Detailed chemistry and turbulence-chemistry interaction need to be properly taken into account for a realistic combustion simulation of IC engines where advanced combustion modes, multiple injections and stratified combustion involve a wide range of combustion regimes and require a proper description of several phenomena such as auto-ignition, flame stabilization, diffusive combustion and lean premixed flame propagation. To this end, different approaches are applied and the most used ones rely on the well-stirred reactor or flamelet assumption. However, well-mixed models do not describe correctly flame structure, while unsteady flamelet models cannot easily predict premixed flame propagation and triple flames. A possible alternative for them is represented by transported probability density functions (PDF) methods, which have been applied widely and effectively for modeling turbulent reacting flows under a wide range of combustion regimes. For IC engine simulations, the most promising ones are the Eulerian field PDF methods (SEF) whose formulation was originally proposed by Valiño and Sabel'nikov.
Technical Paper
2014-04-01
Edoardo Sabbioni, Federico Cheli, Michele Vignati, Stefano Melzi
In recent years, concerns for environmental pollution and oil price stimulated the demand for vehicles based on technologies alternative to traditional IC engines. Nowadays several carmakers include hybrid vehicles among their offer and first full electric vehicles appear on the market. Among the different layout of the electric power-train, four in-wheel motors appear to be one of the most attractive. Besides increasing the inner room, this architecture offers the interesting opportunity of easily and efficiently distribute the driving/braking torque on the four wheels. This characteristic can be exploited to generate a yaw moment (torque vectoring) able to increase lateral stability and to improve the handling of a vehicle. The present paper presents and compares two different torque vectoring control strategies for an electric vehicle with four in-wheel motors. Performances of the control strategies are evaluated by means of numerical simulations of open and closed loop maneuvers. Energy demands of the two control strategies are also estimated.
Technical Paper
2014-04-01
Thuong Nguyen, Peter Janas, Tommaso Lucchini, Gianluca D'Errico, Sebastian Kaiser, Andreas Kempf
Abstract In this study two different simulation approaches to large eddy simulation of spark-ignition engines are compared. Additionally, some of the simulation results are compared to experimentally obtained in-cylinder velocity measurements. The first approach applies unstructured grids with an automated meshing procedure, using OpenFoam and Lib-ICE with a mapping approach. The second approach applies the efficient in-house code PsiPhi on equidistant, Cartesian grids, representing walls by immersed boundaries, where the moving piston and valves are described as topologically connected groups of Lagrangian particles. In the experiments, two-dimensional two-component particle image velocimetry is applied in the central tumble plane of the cylinder of an optically accessible engine. Good agreement between numerical results and experiment are obtained by both approaches.
Technical Paper
2013-09-08
Stephanie Stockar, Marcello Canova, Yann Guezennec, Augusto Della Torre, Gianluca Montenegro, Angelo Onorati
The automotive industry is striving to adopt model-based engine design and optimization procedures to reduce development time and costs. In this scenario, first-principles gas dynamic models predicting the mass, energy and momentum transport in the engine air path system with high accuracy and low computation effort are extremely important today for performance prediction, optimization and cylinder charge estimation and control. This paper presents a comparative study of two different modeling approaches to predict the one-dimensional unsteady compressible flow in the engine air path system. The first approach is based on a quasi-3D finite volume method, which relies on a geometrical reconstruction of the calculation domain using networks of zero-dimensional elements. The second approach is based on a model-order reduction procedure that projects the nonlinear hyperbolic partial differential equations describing the 1D unsteady flow in engine manifolds onto a predefined basis. The two models are compared against experimental data obtained from a single cylinder engine for motorcycle applications.
Technical Paper
2013-09-08
Gianluca Montenegro, Augusto Della Torre, Tarcisio Cerri, Giulio Lenzi, Andrea Fioravanti, Paolo Badalassi, Francesco Maiani
In this work a multilevel CFD analysis have been applied for the design of an intake air-box with improved characteristics of noise reduction and fluid dynamic response. The approaches developed and applied for the optimization process range from the 1D to fully 3D CFD simulation, exploring hybrid approaches based on the integration of a 1D model with quasi-3D and 3D tools. In particular, the quasi-3D strategy is exploited to investigate several configurations, tailoring the best trade-off between noise abatement at frequencies below 1000 Hz and optimization of engine performances. Once the best configuration has been defined, the 1D-3D approach has been adopted to confirm the prediction carried out by means of the simplified approach, studying also the impact of the new configuration on the engine performances. The calculations have been further validated by an extensive experimental campaign carried out not only on the test bench for engine performance analysis but also on an acoustic test bench developed by the University of Florence.
Technical Paper
2013-09-08
Federico Piscaglia, Andrea Montorfano, Angelo Onorati
The current development to set up an automatic procedure for automatic mesh generation and automatic mesh motion for internal combustion engine simulation in OpenFOAM®-2.2.x is here described. In order to automatically generate high-quality meshes of cylinder geometries, some technical issues need to be addressed: 1) automatic mesh generation should be able to control anisotropy and directionality of the grid; 2) during piston and valve motion, cells and faces must be introduced and removed without varying the overall area and volume of the cells, to avoid conservation errors. In particular, interpolation between discrete fields is frequent in computational physics: the use of adaptive and non-conformal meshes necessitates the interpolation of fields between different mesh regions. Interpolation problems also arise in areas such as model coupling, model initialization and visualisation. This paper discusses the efficient implementation of the sliding interface, an algorithm to handle motion and topological changes in a moving-mesh Finite Volume Method (FVM) framework, that has been implemented to work with the newest mesh handling strategy of OpenFOAM®-2.2.x in a massively parallel environment.
Technical Paper
2013-09-08
Mattia Bissoli, Alberto Cuoci, Alessio Frassoldati, Tiziano Faravelli, Eliseo Ranzi, Tommaso Lucchini, Gianluca D'Errico, Francesco Contino
A new multi-zone model for the simulation of HCCI engine is here presented. The model includes laminar and turbulent diffusion and conduction exchange between the zones and the last improvements on the numerical aspects. Furthermore, a new strategy for the zone discretization is presented, which allows a better description of the near-wall zones. The aim of the work is to provide a fast and reliable model for carrying out chemical analysis with detailed kinetic schemes. A preliminary sensitivity analysis allows to verify that 10 zones are a convenient number for a good compromise between the computational effort and the description accuracy. The multi-zone predictions are then compared with the CFD ones to find the effective turbulence parameters, with the aim to describe the near-wall phenomena, both in a reactive and non-reactive cases. Finally, the model is validated against experimental data of HCCI combustion of fossil and bio-fuels (n-heptane, methyl-hexanoate, and methyl-decanote).
Technical Paper
2013-09-08
Tommaso Lucchini, Marco Fiocco, Angelo Onorati, Alessandro Montanaro, Luigi Allocca, Paolo Sementa, Bianca Maria Vaglieco, Francesco Catapano
This paper is focused on the development and application of a CFD methodology that can be applied to predict the fuel-air mixing process in stratified charge, sparkignition engines. The Eulerian-Lagrangian approach was used to model the spray evolution together with a liquid film model that properly takes into account its effects on the fuel-air mixing process into account. However, numerical simulation of stratified combustion in SI engines is a very challenging task for CFD modeling, due to the complex interaction of different physical phenomena involving turbulent, reacting and multiphase flows evolving inside a moving geometry. Hence, for a proper assessment of the different sub-models involved a detailed set of experimental optical data is required. To this end, a large experimental database was built by the authors. In particular, the spray morphology was characterized in detail inside a constant volume vessel, where images were acquired by a CCD camera and then post-processed to evaluate the spray penetration and cone-angles.
Technical Paper
2013-09-08
Gianluca D'Errico, Tommaso Lucchini, Alessandro Stagni, Alessio Frassoldati, Tiziano Faravelli, Eliseo Ranzi
Detailed chemistry represents a fundamental pre-requisite for a realistic simulation of combustion process in Diesel engines to properly reproduce ignition delay and flame structure (lift-off and soot precursors) in a wide range of operating conditions. In this work, the authors developed reduced mechanisms for n-dodecane starting from the comprehensive kinetic mechanism developed at Politecnico di Milano, well validated and tested in a wide range of operating conditions [1]. An algorithm combining Sensitivity and Flux Analysis was employed for the present skeletal reduction. The size of the mechanisms can be limited to less than 100 species and incorporates the most important details of low-temperature kinetics for a proper prediction of the ignition delay. Furthermore, the high-temperature chemistry is also properly described both in terms of reactivity and species formation, including unsaturated compounds such as acetylene, whose concentration controls soot formation. The consistency between reduced and detailed mechanism was verified in several reference experiments.
Technical Paper
2013-04-08
Edoardo Sabbioni, Federico Cheli, Stefano Melzi
The present paper investigates possible enhancement of ESP performance associated with the use of smart tires. In particular a novel control logic based on a direct feedback on the longitudinal forces developed by the four tires is considered. The control logic was developed using a simulation tool including a 14 dofs vehicle model and a smart tires emulator. Performance of the control strategy was evaluated in a series of handling maneuvers. The same maneuvers were performed on a HiL test bench interfacing the same vehicle model with a production ESP ECU. Results of the two logics were analyzed and compared.
Technical Paper
2013-04-08
Hua Wang, Lucio Araneo, Aldo Coghe
The flow field resulting from injecting a gas jet into a crossflow confined in a narrow square duct has been studied under steady regime using schlieren imaging and laser Doppler velocimetry (LDV). This transparent duct is intended to simulate the intake port of an internal combustion engine fueled by gaseous mixture, and the jet is issued from a round nozzle. The schlieren images show that the relative small size of the duct would confine the development of the transverse jet, and the interaction among jet and sidewalls strongly influences the mixing process between jet and crossflow. The mean velocity and turbulence fields have been studied in detail through LDV measurements, at both center plane and several cross sections. The well-known flow feature formed by a counter rotating vortex pair (CVP) has been observed, which starts to appear at the jet exit section and persists far downstream contributing to enhancing mixing process. In addition, jets of different gases have been investigated with various injection orientations, aiming to fully understand the behaviors of transverse jet and the mixing process in the simulated intake port under wide practical conditions.
Technical Paper
2013-04-08
Volker Schmeisser, Michel Weibel, Laura Sebastian Hernando, Isabella Nova, Enrico Tronconi, Maria Pia Ruggeri
NH₃/urea SCR is a very effective and widely used technology for the abatement of NOx from diesel exhaust. The SCR mechanism is well understood and the catalyst behavior can be predicted by mathematical models - as long as operation above the temperature limit for AdBlue® injection is considered. The behavior below this level is less understood. During the first seconds up to minutes after cold start, complete NOx abatement can be observed over an SCR catalyst in test bench experiments, together with a significant increase in temperature after the converter (ca. 100 K). In this work these effects have been investigated over a monolith Cu-zeolite SCR catalyst. Concentration step experiments varying NO, NO₂ and H₂O have been carried out in lab scale, starting from room temperature. Further, the interaction of C₃H₆ and CO with NOx over the SCR has been investigated. The effects observed during cold start have been reproduced successfully at lab scale, providing insight into the prevailing mechanisms.
Technical Paper
2013-04-08
Tommaso Lucchini, Luca Cornolti, Gianluca Montenegro, Gianluca D'Errico, Marco Fiocco, Atsushi Teraji, Taisuke Shiraishi
A correct prediction of the initial stages of the combustion process in SI engines is of great importance to understand how local flow conditions, fuel properties, mixture stratification and ignition affect the in-cylinder pressure development and pollutant formation. However, flame kernel growth is governed by many interacting processes including energy transfer from the electrical circuit to the gas phase, interaction between the plasma channel and the flow field, transition between different combustion regimes and gas expansion at very high temperatures. In this work, the authors intend to present a comprehensive, multi-dimensional model that can be used to predict the initial combustion stages in SI engines. In particular, the spark channel is represented by a set of Lagrangian particles where each one of them acts as a single flame kernel. Each particle is convected by the gas flow and its growth is governed by flame speed and thermal expansion due to the energy transfer from the electrical circuit.
Technical Paper
2013-04-08
Federico Piscaglia, Andrea Montorfano, Angelo Onorati
The implementation and the combination of advanced boundary conditions and subgrid scale models for Large Eddy Simulation (LES) in the multi-dimensional open-source CFD code OpenFOAM® are presented. The goal is to perform reliable cold flow LES simulations in complex geometries, such as in the cylinders of internal combustion engines. The implementation of a boundary condition for synthetic turbulence generation upstream of the valve port and of the compressible formulation of the Wall-Adapting Local Eddy-viscosity sgs model (WALE) is described. The WALE model is based on the square of the velocity gradient tensor and it accounts for the effects of both the strain and the rotation rate of the smallest resolved turbulent fluctuations and it recovers the proper y₃ near-wall scaling for the eddy viscosity without requiring dynamic procedure; hence, it is supposed to be a very reliable model for ICE simulation. Validation of the implemented models has been performed separately on two steady state flow benches, where experimental data were available: a backward facing step geometry and a simple IC engine geometry with one axed central valve.
Technical Paper
2013-04-08
Stefano Bottelli, Harald Waschl, Sergio Savaresi, Luigi del Re, Simone Formentin
Although the application of cylinder pressure sensors to gain insight into the combustion process is not a novel topic itself, the recent availability of inexpensive in-cylinder pressure sensors has again prompted an upcoming interest for the utilization of the cylinder pressure signal within engine control and monitoring. Besides the use of the in-cylinder pressure signal for combustion analysis and control the information can also be used to determine related quantities in the exhaust or intake manifold. Within this work two different methods to estimate the pressure inside the exhaust manifold are proposed and compared. In contrary to first principle based approaches, which may require time extensive parameterization, alternative data driven approaches were pursued. In the first method a Principle Component Analysis (PCA) is applied to extract the cylinder pressure information and combined with a polynomial model approach. In the second method an approach which uses the full pressure trace over the crank angle, also in combination with a polynomial model, is applied.
Technical Paper
2012-09-10
Mehdi Jangi, Gianluca D'Errico, Xue-Song Bai, Tommaso Lucchini
A three dimensional numerical simulation of the ECN “Spray A” is presented. Both primary and secondary breakup of the spray are included. The fuel is n-Dodecane. The n-Dodecane kinetic mechanism is modeled using a skeletal mechanism that consists of 103 species and 370 reactions [9]. The kinetic mechanism is computationally heavy when coupled with three dimensional numerical simulations. Multidimensional chemistry coordinate mapping (CCM) approach is used to speedup the simulation. CCM involves two-way mapping between CFD cells and a discretized multidimensional thermodynamic space, the so called multidimensional chemistry coordinate space. In the text, the cells in the discretized multidimensional thermodynamic space are called zone to discriminate them from the CFD cells. In this way, the CFD cells which are at the similar thermodynamic state are identified and grouped into a unique zone. The stiff ODEs operates only on the zones containing at least one CFD cell. This zones are called “active zones”.
Technical Paper
2012-04-16
Stephan Stadlbauer, Daniel Alberer, Markus Hirsch, Simone Formentin, Christian Benatzky, Luigi del Re
NOx and PM are the critical emissions to meet the legislation limits for diesel engines. Often a value for these emissions is needed online for on-board diagnostics, engine control, exhaust aftertreatment control, model-based controller design or model-in-the-loop simulations. Besides the obvious method of measuring these emissions, a sensible alternative is to estimate them with virtual sensors. A lot of literature can be found presenting different modeling approaches for NOx emissions. Some are very close to the physics and the chemical reactions taking place inside the combustion chamber, others are only given by adapting general functions to measurement data. Hence, generally speaking, there is not a certain method which is seen as the solution for modeling emissions. Finding the best model approach is not straightforward and depends on the model application, the available measurement channels and the available data set for calibration. This paper evaluates three different already published virtual sensor approaches for NOx engine raw emissions of a heavy-duty diesel engine in off-road applications.
Technical Paper
2012-04-16
Gianluca Montenegro, Angelo Onorati, Tarcisio Cerri, Augusto Della Torre
Increasing demands on the capabilities of engine simulation and the ability to accurately predict both performance and acoustics has lead to the development of several numerical tools to help engine manufacturers during the prototyping stage. The aid of CFD tools (3D and 1D) can remarkably reduce the duration and the costs of this stage. The need of achieving good accuracy, along with acceptable computational runtime, has given the spur to the development of a geometry based quasi-3D approach. This is designed to model the acoustics and the fluid dynamics of both intake and exhaust system components used in internal combustion engines. Models of components are built using a network of quasi-3D cells based primarily on the geometry of the system. The solution procedure is based on an explicitly time marching staggered grid approach making use of a flux limiter to prevent numerical instabilities. The equations of mass and energy are solved at cell centers whereas the momentum equation at cell connections (ports).
Technical Paper
2012-04-16
Edoardo Sabbioni, Marco Sbrosi, Daniele Rocchi, Riccardo Galeotti
In the paper, a procedure to assess the quality of the shielding effect of wind barriers to protect large sided vehicles crossing the wake of a bridge pylon under cross wind conditions is proposed. The methodology is based on Multi-Body simulations of the response of the vehicle-driver system when it is subjected to the sudden change of the aerodynamic forces due to the wind-tower interaction. The aerodynamic forces that are instantaneously acting on the vehicle are computed according to a force distribution approach that relies on wind tunnel tests that may be performed on still scaled models. From the knowledge of the aerodynamic force distribution along the vehicle at different yaw angles and of the mean wind profile across the tower wake, the aerodynamic force, acting on the moving vehicle, is reconstructed at each time step taking into consideration the actual vehicle-driver dynamics. The numerical procedure is applied to compare the different responses that the vehicle-driver system exhibits in presence or absence of wind barriers close to the tower.
Technical Paper
2012-04-16
Federico Piscaglia, Andrea Montorfano, Angelo Onorati
In this paper a three-dimensional time-domain CFD approach has been employed to predict and analyze the acoustic attenuation performance of complex perforated muffler geometries, where strong 3D effects limit the validity of the use of one-dimensional models. A pressure pulse has been imposed at the inlet to excite the wave motion, while unsteady flow computation have been performed to acquire the time histories of the pressures upstream and downstream of the silencer. Pressures in the time domain have been then transformed to acoustic pressures in the frequency domain, to predict the transmission loss. In order to achieve reliable predictions of the acoustic attenuation, especially above the plane wave cut-off frequency, an advanced non-reflecting boundary condition to model the anechoic termination, based on the NSCBC characteristic theory, has been implemented in a multidimensional open-source CFD code and it has been used together with a time dependent compressible Navier Stokes equation solver.
Technical Paper
2012-04-16
Stefano Melzi, Marco Sbrosi, Edoardo Sabbioni, Vincenzo d'alessandro
Hydroplaning represents a threat for riding safety since a wedge of water generated at the tire-road interface can lift tires from the ground thus preventing the development of tangential contact forces. Under this condition directionality and stability of the vehicle can be seriously compromised. The paper aims at characterizing the tire lateral response while approaching the hydroplaning speed: several experimental tests were carried out on a special test track covered with a 8-mm high water layer using a vehicle equipped with a dynamometric hub on the front left wheel. A series of swept sine steer maneuvers were performed increasing the vehicle speed in order to reach a full hydroplaning condition. Variations of tire cornering stiffness and relaxation length were investigated while the vehicle approaches the hydroplaning speed. Experimental tests stated that a residual capability of generating lateral forces is still present also close to the full hydroplaning condition.
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