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This paper presents a methodology for simulating Fluid Structure Interaction (FSI) for a typical vehicle bonnet (hood) under a range of onset flow conditions. The hood was chosen for this study, as it is one of the panels most prone to vibration; particularly given the trend to make vehicle panels lighter. Among the worst-case scenarios for inducing vibration is a panel being subjected to turbulent flow from vehicle wakes, and the sudden peak loads caused by emerging from a vehicle wake. This last case is typical of a passing manoeuvre, with the vehicle suddenly transitioning from being immersed in the wake of the leading vehicle, to being fully exposed to the free-stream flow. The transient flowfield was simulated for a range of onset flow conditions that could potentially be experienced on the open road, which may cause substantial vibration of susceptible vehicle panels.

The focus of evaluating yaw characteristics in automotive aerodynamics has been primarily with regards to the effects of crosswind on vehicle handling. However, changes to drag that the vehicle experiences due to prevalent on-road crosswind can also be significant, even at low yaw angles. Using wind tunnel testing, it is possible to quickly determine the static yaw performance of the vehicle by rotating the vehicle on a turntable to different yaw angles during a single wind tunnel run. However, this kind of testing does not account for dynamic crosswind effects or non-uniform crosswind such as with natural on-road turbulence. Alternatively, numerical simulations using computational fluid dynamics (CFD) can be used to evaluate yaw performance. In this paper, Exa's PowerFLOW is used to examine two alternative methods of simulating aerodynamic performance in the presence of realistic on-road crosswind for the Tesla Model S sedan.

Contamination of vehicle rear surfaces is a significant issue for customers. Along with being unsightly, it can degrade the performance of rear camera systems and lighting, prematurely wear rear screens and wipers, and transfer soil to customers moving goods through the rear tailgate. Countermeasures, such as rear camera wash or automated deployment add expense and complexity for OEMs. This paper presents a rear surface contamination model for a fully detailed SUV based on the use of a highly-resolved time-accurate aerodynamic simulation realised through the use of a commercial Lattice-Boltzmann solver, combined with Lagrangian Particle Tracking to simulate droplet advection and surface water dynamics via a thin film model. Droplet break-up due to aerodynamic shear is included, along with splash and stripping from the surface film. The effect of two-way momentum coupling is included in a sub-set of simulations.

Historically vehicle aerodynamic development has focused on testing under idealised conditions; maintaining measurement repeatability and precision in the assessment of design changes. However, the on-road environment is far from ideal: natural wind is unsteady, roadside obstacles provide additional flow disturbance, as does the presence of other vehicles. On-road measurements indicate that turbulence with amplitudes up to 10% of vehicle speed and dominant length scales spanning typical vehicle sizes (1-10 m) occurs frequently. These non-uniform flow conditions may change vehicle aerodynamic behaviour by interfering with separated turbulent flow structures and increasing local turbulence levels. Incremental improvements made to drag and lift during vehicle development may also be affected by this non-ideal flow environment. On-road measurements show that the shape of the observed turbulence spectrum can be generalised, enabling the definition of representative wind conditions.

This paper implements a coupled approach to integrate the internal nozzle flow and the ensuing fuel spray using a Volume-of-Fluid (VOF) method in the CONVERGE CFD software. A VOF method was used to model the internal nozzle two-phase flow with a cavitation description closed by the homogeneous relaxation model of Bilicki and Kestin [1]. An Eulerian single velocity field approach by Vallet et al. [2] was implemented for near-nozzle spray modeling. This Eulerian approach considers the liquid and gas phases as a complex mixture with a highly variable density to describe near nozzle dense sprays. The mean density is obtained from the Favreaveraged liquid mass fraction. The liquid mass fraction is transported with a model for the turbulent liquid diffusion flux into the gas.

The Reynolds stress turbulence model (RSM) has been developed to go beyond the Boussinesq hypothesis and to improve turbulence modeling of flows with significant mean streamline curvature and secondary flow. In this paper the RSM in commercial CFD software CONVERGE is tested for its performance and robustness when applying to complex flows. Several validation cases including flow over flat plate, vortex combustor, diesel engine spray and combustion were selected to test the RSM. The swirling flow in vortex combustor, non-reacting but vaporizing ECN Spray A (free jet) and Sandia small bore diesel engine case are used to demonstrate the benefits of the RSM over the widely used RNG k-epsilon model without model tuning. The vortex combustor case shows the RSM can provide good prediction for strong swirling flow. ECN spray A case was used to demonstrate that the RSM can accurately predict the liquid and vapor penetration lengths of a free jet under diesel engine conditions.

The objective of this project was to model and study the interior noise in an Off-Highway Truck cab using Statistical Energy Analysis (SEA). The analysis was performed using two different modeling techniques. In the first method, the structural members of the cab were modeled along with the panels and the interior cavity. In the second method, the structural members were not modeled and only the acoustic cavity and panels were modeled. Comparison was done between the model with structural members and without structural members to evaluate the necessity of modeling the structure. Correlation between model prediction of interior sound pressure and test data was performed for eight different load conditions. Power contribution analysis was performed to find dominant paths and 1/3rd octave band frequencies.

This paper describes the design, development and validation of a muffler for reducing exhaust noise from a commercial tele-handler. It also describes the procedure for modeling and optimizing the exhaust muffler along with experimental measurement for correlating the sound transmission loss (STL). The design and tuning of the tele-handler muffler was based on several factors including overall performance, cost, weight, available space, and ease of manufacturing. The analysis for predicting the STL was conducted using the commercial software LMS Virtual Lab (LMS-VL), while the experimental validation was carried out in the laboratory using the two load setup. First, in order to gain confidence in the applicability of LMS-VL, the STL of some simple expansion mufflers with and without extended inlet/outlet and perforations was considered. The STL of these mufflers were predicted using the traditional plane wave transfer matrix approach.

Previous work by the authors showed the development of an aerodynamic CFD model using the Lattice Boltzmann Method for simulating vehicles inside the IVK Model-Scale Wind-Tunnel test-section. In both experiment and simulation, alternate configurations of the wind-tunnel geometry were studied to change the pressure distribution in the wind-tunnel test section, inducing a reduction in aerodynamic drag due to interference between the wind-tunnel geometry and the pressure on the surface of the vehicle. The wind-tunnel pressure distribution was modified by adding so-called “stagnation bodies” inside the collector to create blockage and to increase the pressure in the rear portion of the test section. The primary purpose of previous work was to provide a validated CFD approach for modeling wind-tunnel interference effects, so that these effects can be understood and accounted for when designing vehicles.

For most car manufacturers, aerodynamic noise is becoming the dominant high frequency noise source (≻500 Hz) at highway speeds. Design optimization and early detection of issues related to aeroacoustics remain an experimental art implying high cost prototypes, expensive wind tunnel sessions, and potentially late design changes. To reduce the associated costs as well as development times, there is strong motivation for the development of a reliable numerical prediction capability. This paper presents a computational approach that can be used to predict the vehicle interior noise from the greenhouse wind noise sources, during the early stages of the vehicle developmental process so that design changes can be made to improve the wind noise performance of the vehicle.

New tire model is under development in European Commission research project called VERT (Vehicle Road Tire Interaction, BRPR-CT97-0461). The objective of the project is to create a physical model for tire/surface contact simulation. One of the subtasks has been to develop a method for snow surface characterization. The aim is simulate winter tire on snow surface with FEM software. This kind of simulation has been earlier done with snow model parameters from laboratory experiments. A snow shear box device has been developed in Helsinki University of Technology to measure mechanical properties of snow in field conditions. Both shear and compression properties can be measured with the device. With the device, a large number of snow measurements have been done at the same time with VERT winter tire testing in Nokian Tyres'' test track in Ivalo Finland. Measurement data have been postprocessed afterwards and parameters for material models have been evaluated.

A modified version of the Laminar and Turbulent Characteristic Time combustion model and the Hiroyasu-Magnussen soot model have been implemented in the flow solver Star-CD. Combustion simulations of three DI diesel engines, utilizing the standard k-ε turbulence model and a modified version of the RNG k-ε turbulence model, have been performed and evaluated with respect to combustion performance and emissions. Adjustments of the turbulent characteristic combustion time coefficient, which were necessary to match the experimental cylinder peak pressures of the different engines, have been justified in terms of non-equilibrium turbulence considerations. The results confirm the existence of a correlation between the integral length scale and the turbulent time scale. This correlation can be used to predict the combustion time scale in different engines.

The one-equation subgrid scale model for the Large Eddy Simulation (LES) turbulence model has been compared to the popular k-ε RNG turbulence model in very different sized direct injection diesel engines. The cylinder diameters of these engines range between 111 and 200 mm. This has been an initial attempt to study the effect of LES in diesel engines without any modification to the combustion model being used in its Reynolds-averaged Navier-Stokes (RANS) form. Despite some deficiencies in the current LES model being used, it already gave much more structured flow field with approximately the same kind of accuracy in the cylinder pressure predictions than the k-ε RNG turbulence model.

A numerical study has been carried out to assess the effects of needle movement and internal nozzle flow on spray formation for a multi-hole Gasoline Direct Injection system. The coupling of nozzle flow and spray formation is dynamic in nature and simulations with pragmatic choice of spatial and temporal resolutions are needed to analyze the sprays in a GDI system. The dynamic coupling of nozzle flow and spray formation will be performed using an Eulerian-Lagrangian Spray Atomization (ELSA) approach. In this approach, the liquid fuel will remain in the Eulerian framework while exiting the nozzle, while, depending on local instantaneous liquid concentration in a given cell and amount of liquid in the neighboring cells, part of the liquid mass will be transferred to the Lagrangian framework in the form of Lagrangian parcels.

Technologies that provide potential for significant improvements in engine efficiency include, engine downsizing/downspeeding (enabled by advanced boosting systems such as an electrically driven compressor), waste heat recovery through turbocompounding or organic Rankine cycle and 48 V mild hybridization. FEV’s Integrated Turbocompounding/Waste Heat Recovery (WHR), Electrification and Supercharging (FEV-ITES) is a novel approach for integration of these technologies in a single unit. This approach provides a reduced cost, reduced space claim and an increase in engine efficiency, when compared to the independent integration of each of these technologies. This approach is enabled through the application of a planetary gear system. Specifically, a secondary compressor is connected to the ring gear, a turbocompounding turbine or organic Rankine cycle (ORC) expander is connected to the sun gear, and an electric motor/generator is connected to the carrier gear.

A set of reduced chemical mechanisms was developed for use in multi-dimensional engine simulations of premixed gasoline combustion. The detailed Primary Reference Fuel (PRF) mechanism (1034 species, 4236 reactions) from Lawrence Livermore National Laboratory (LLNL) was employed as the starting mechanism. The detailed mechanism, referred to here as LLNL-PRF, was reduced using a technique known as Parallel Direct Relation Graph with Error Propagation and Sensitivity Analysis. This technique allows for efficient mechanism reduction by parallelizing the ignition delay calculations used in the reduction process. The reduction was performed for a temperature range of 800 to 1500 K and equivalence ratios of 0.5 to 1.5. The pressure range of interest was 0.75 bar to 40 bar, as dictated by the wide range in spark timing cylinder pressures for the various cases. In order to keep the mechanisms relatively small, two reductions were performed.

To address the need of increasing fuel economy requirements, automotive Original Equipment Manufacturers (OEMs) are increasing the number of turbocharged engines in their powertrain line-ups. The turbine-driven technology uses a forced induction device, which increases engine performance by increasing the density of the air charge being drawn into the cylinder. Denser air allows more fuel to be introduced into the combustion chamber, thus increasing engine performance. During the inlet air compression process, the air is heated to temperatures that can result in pre-ignition resulting and reduced engine functionality. The introduction of the charge air cooler (CAC) is therefore, necessary to extract heat created during the compression process. The present research describes the physics and develops the optimized simulation method that defines the process and gives insight into the development of CACs.

Combustion is governed by only two phenomena: chemical reactions and mixing (i.e., transport of energy, species, and momentum). A Reynolds Averaged Navier-Stokes (RANS) turbulence model is commonly employed to account for the enhanced mixing due to the presence of turbulence in fluid flow. A RANS turbulence model enhances mixing by introducing a turbulent viscosity. The addition of a turbulent viscosity not only enhances mixing but it also eliminates smaller scales in the CFD simulation. Even though the turbulent viscosity eliminates smaller scales, it is common for RANS engine combustion simulations to be under-resolved. The lack of sufficient mesh resolution to resolve the remaining scales in a RANS combustion simulation may result in a significant sub-grid term that needs to be modeled. In the context of combustion simulation, it is shown that frequently this sub-grid term is significantly more important than Turbulent Chemistry Interaction terms (TCI).

This paper reports an experimental and numerical investigation on the spatial and temporal liquid- and vapor-phase distributions of diesel fuel spray under engine-like conditions. The high pressure diesel spray was investigated in an optically-accessible constant volume combustion vessel for studying the influence of the k-factor (0 and 1.5) of a single-hole axial-disposed injector (0.100 mm diameter and 10 L/d ratio). Measurements were carried out by a high-speed imaging system capable of acquiring Mie-scattering and schlieren in a nearly simultaneous fashion mode using a high-speed camera and a pulsed-wave LED system. The time resolved pair of schlieren and Mie-scattering images identifies the instantaneous position of both the vapor and liquid phases of the fuel spray, respectively. The studies were performed at three injection pressures (70, 120, and 180 MPa), 23.9 kg/m3 ambient gas density, and 900 K gas temperature in the vessel.

The climate inside a vehicle cabin is affected by the performance of the vehicle HVAC system, the thermal characteristics of the vehicle structure and the components, as well as the external environmental conditions. Due to the complex interactions among these various factors, the flow field and the temperature distribution can be very complicated. The need for a fully three-dimensional transient analysis is increasing in order to provide sufficiently detailed information that can be used to improve the vehicle design. In this study, a numerical simulation methodology to predict the local climate conditions in a passenger vehicle cabin is presented. The convective heat transfer from both the exterior and the interior of the cabin were calculated by three dimensional CFD simulations using a Lattice-Boltzmann method based flow solver. The conduction and the radiation effects including the solar loading were solved using a finite-difference based radiation-conduction thermal solver.