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This paper presents typical flow structures around a 60%-scale wind-tunnel model of a Formula One (F1) car, using planar particle image velocimetry (PIV). The customized PIV system is permanently installed in a wind tunnel to help aerodynamicists in the development loop. The PIV results enhance the understanding of the mean velocity field in the two-dimensional plane in some important areas of the car, such as the front-wheel wake and the underfloor flow. These real phenomena obtained in the wind tunnel also help maintain the accuracy of simulations using computational fluid dynamics (CFD) by allowing regular checking of the correlation with the real-world counterpart. This paper first surveys recent literature on unique flow structures around the rotating exposed wheel, mostly that on the isolated wheel, and then gives the background to F1 aerodynamics in the late 2000s.

This paper provides an overview of the design and commissioning results for the DaimlerChrysler full-scale vehicle Aeroacoustic Wind Tunnel (AAWT) brought online in 2002. This wind tunnel represents the culmination of the plan for aeroacoustic facilities at the DaimlerChrysler Corporation Technical Center (DCTC) in Auburn Hills, Michigan. The competing requirements of excellent flow quality, low background noise, and constructed cost within budget were optimized using Computational Fluid Dynamics, extensive acoustic modeling, and a variety of scale-model experimental results, including dedicated experiments carried out in the 3/8-scale pilot wind tunnel located at DCTC. The paper describes the project history, user requirements, and design philosophy employed in realizing the facility. The AAWT meets all of DaimlerChrylser's performance targets, and was delivered on schedule. The commissioning results presented in this paper show its performance to be among the best in the world.

The key challenge in designing a high power density fuel cell is to reduce oxygen transport loss due to liquid water. However, liquid water transport from catalyst layers to channels under operating conditions is not completely understood. Toyota developed a high resolution space and time liquid water visualization technique using synchrotron x-ray (Spring-8) radiography. In addition, a simulation method was created based on computational fluid dynamics (CFD) to identify the cell performance relationship to water distribution. The relationship among gas diffusion layer (GDL) parameters, water distribution, and fuel cell performance was clarified by combining the techniques Toyota developed.

Buffeting is a wind noise of high intensity and low frequency in a moving vehicle when a window or sunroof is open and this noise makes people in the passenger compartment very uncomfortable. In this paper, side window buffeting was simulated for a typical SUV using the commercial CFD software Fluent 6.0. Buffeting frequency and intensity were predicted in the simulations and compared with the corresponding experimental wind tunnel measurement. Furthermore, the effects of several parameters on buffeting frequency and intensity were also studied. These parameters include vehicle speed, yaw angle, sensor location and volume of the passenger compartment. Various configurations of side window opening were considered. The effects of mesh size and air compressibility on buffeting were also evaluated. The simulation results for some baseline configurations match the corresponding experimental data fairly well.

Toyota Motor Corporation has developed a new 2.0L Inline 4- Cylinder (I4) Gasoline Direct Injection Engine, the second Naturally Aspirated (NA) engine of the Toyota New Global Architecture (TNGA) engine series, to meet our customers’ expectations for drivability, performance, and fuel economy. The high speed combustion technologies adopted previously in our 2.5 L NA conventional and Hybrid Vehicle (HV) engines for the 2018 Toyota Camry are necessary for high engine power and thermal efficiency. To adopt our high speed combustion technology on engines with different displacements, the turbulence intensity has been defined as the target index of combustion speed. The basic engine structure has been revised by using Computational Fluid Dynamics (CFD) analysis to achieve the combustion target.

Combustion in a lean atmosphere diluted with a large amount of air can greatly improve fuel efficiency by reducing cooling loss [1, 2]. On the other hand, when air-fuel mixture in cylinder becomes lean, the turbulent combustion speed will decrease, resulting in problems such as the generation of unburned hydrocarbon (HC) and combustion instability [3, 4]. In order to solve these problems, it is important to increase the turbulence intensity and combustion speed [5, 6, 7, 8, 9, 10]. When designing combustion in cylinder by using Computational Fluid Dynamics (CFD), K-epsilon model is widely used for a turbulence model, and the calculated turbulence energy k or turbulence intensity u’ have been used as important indices of combustion velocity [11, 12].

An impinging-flow based methodology of enhancing the heat transfer in the grooves of a lockup clutch is proposed and studied. In order to evaluate its efficacy and reveal the mechanism, the three-dimensional flow within the groove was solved as a conjugate heat transfer problem in a rotating reference frame using the commercial CFD code FLUENT. The turbulence characteristics were predicted using k-ε model. The comparison of cooling effect was made between a simple baseline groove pattern and a typical flow-impingement based groove pattern of the same groove-to-total area ratio in terms of heat rejection ratio, maximum surface temperature, and heat transfer coefficient. It is found that more heat can be rejected with the impinging-flow based groove from the friction surface than with the baseline while the maximum surface temperature is lower in the former case.

Experimental and computational simulation techniques were concurrently employed throughout the aerodynamic development of the NASCAR Dodge Intrepid R/T in order to achieve a greater understanding of the complex flow fields involved. With less than 500 days to design, understand, and build a competitive vehicle, the development team utilized a closed loop approach to testing. Scale wind tunnel models and Computational Fluid Dynamics (CFD) were used to identify program direction and to speed the development cycle versus the traditional process of full scale testing. This paper will detail the process and application of both the experimental and computational techniques used in the aerodynamic development of the Intrepid R/T race vehicle, primarily focusing on the earlier stages that led to its competition introduction at the start of the 2001 season.

This paper describes a water-level prediction method for the air intake duct using multivariate analysis. When a vehicle runs on a submerged proving ground, in some cases the water level around the air intake duct rises. Although the rise in water level can be measured experimentally in actual vehicles, the design factors that determine the water level are not yet fully understood. The first step in understanding the factors for determining the water level on front-engine and front-drive (FF) -type vehicles is to establish a water level prediction technique. This is accomplished by the development of an original Computational Fluid Dynamics (CFD) analysis method capable of accurately simulating a free surface. The next step is to conduct multivariate analysis based on the results of parametric studies using this CFD analysis method that leads to the factors determining the water level at the air intake duct.

Computational fluid dynamic (CFD) is widely used to develop engine combustion. Especially the in-cylinder spray calculation is important in order to resolve the issues of direct injection gasoline engines (e.g., particulate matter (PM) and oil dilution caused by fuel wetting on the cylinder walls). Conventional spray calculation methods require fitting based on measurements of spray characteristics such as penetration and droplet diameter (i.e., the Sauter mean diameter (SMD)). Particularly in the case of slit nozzle shapes that widen from the inlet to the outlet to form a fan-shaped spray, fitting the shape of spray is a complex procedure because the flow inside the nozzle is not uniform. In response, a new calculation method has been developed that eliminates the need for spray shape fitting by combining calculations of the Eulerian multiphase and the Lagrangian multiphase.

Conventional CFD-based shape optimization technology that uses parametric shape modification and optimal solutions searching algorithms has the two problems: (1) outcome of optimized shapes depend on the selection of design parameters made by the designer, and (2) high computational costs. To resolve those problems, two innovative inverse analysis technologies based on the Adjoint Method were developed in previous study: surface geometry deformation sensitivity analysis to identify the locations to be modified, and topology optimization to generate an optimal shape for maximizing the cost function in the constrained design space. However, these technologies are only applicable to steady flows. Since most flows in a vehicle (such as engine in-cylinder flow) are transient, a practical technology for surface geometry sensitivity analysis has been developed based on the Transient Adjoint Method.

To resolve two major problems of conventional CFD-based shape optimization technology: (1) dependence of the outcome on the selection of design parameters, and (2) high computational costs, two types of innovative inverse analysis technologies based on a mathematical theory called the Adjoint Method were developed in previous studies for maximizing an arbitrary hydrodynamic performance aspect as the cost function: surface geometry deformation sensitivity analysis to identify the locations to be modified, and topology optimization to generate an optimal shape. Furthermore, these technologies were extended to transient flows by the application of the transient Adjoint Method theory. However, there are many cases around flow path shapes in vehicles where performance with respect to heat or concentration, such as the total amount of heat transfer or the flow rate of a specific gas component, is very important.

This paper describes the analyses to improve both stratified and homogeneous charge combustion of a gasoline direct injection engine. In this study, computational fluid dynamics (CFD) and high-speed hydrocarbon (HC) measurement were employed to observe the mixture formation process. The analysis of the combustion flame propagation was conducted by in-cylinder visualization and ion current measurement. As a result of the analyses, the following conclusions were made: 1 An oval shaped wall cavity can direct the mixture gas to the vicinity of the spark plug better than a conventional shell-shaped wall cavity. The oval shaped wall cavity can improve fuel consumption and HC emission at stratified charge combustion. 2 A shallow cavity improves the homogenization of mixture gases and wide open throttle (WOT) performance.

The flow within the disengaged wet clutch packs of an automatic transmission has been simulated as a three-dimensional, steady-state, two-phase flow using the commercial computational fluid dynamics (CFD) code FLUENT. The flow within a clutch with ungrooved friction plates was first solved for validating the CFD model, followed by a simulation of the flow within a clutch with grooved friction plates. A group of dimensionless variables have been established for mathematically modeling the drag torque and power loss in clutch packs. The effects of rotating speed of friction plate, pack clearance, and flow rate on drag torque and power loss have been studied.

This paper summarizes the major activities of CFD study on rear window buffeting of production vehicles during the past two years at DaimlerChrysler. The focus of the paper is the attempt to find suitable solutions for buffeting suppression using a developed procedure of CFD simulation with commercial software plus FFT acoustic post-processing. The analysis procedure has been validated using three representative production vehicles and good correlation with wind tunnel tests has been attained which has gained the confidence in solving the buffeting problem. Several attempts have been proposed and tried to find solution for buffeting reduction. Some of them are promising, but feasibility and manufacturability still need discussion. In order to find suitable solution for buffeting reduction, more basic research is necessary, more ideas should be collected, and more joint efforts of CFD and testing are imperative.

Combustion of a lean air-fuel mixture diluted with a large amount of air or Exhaust Gas Recirculation (EGR) gas is one of the important technologies that can reduce thermal NOx and improve gasoline engine fuel economy by reducing cooling loss. On the other hand, lean combustion increases unburned Hydro Carbon (HC) and unburned loss compared to stoichiometric combustion. This is because lean combustion reduces the burning rate of the air-fuel mixture and forms a thick quenching layer near the wall surface. In this study, the relationship between the thickness of the unburned HC and the excess air ratio is analyzed using Laser Induced Fluorescence (LIF) method and Computational Fluid Dynamic (CFD) of combustion. The HC distribution near the engine liner when the excess air ratio is increased is investigated by LIF. As a result, it is found that the quenching distance of the flame in the cylinder is larger for lean conditions than the general single-wall quenching relationship.

NO2 sources of roadside atmosphere at Matsubarabashi monitoring station in Tokyo were investigated analytically. The result showed that contribution of urban background is dominant from November to February and NO oxidation with O3 has large contribution from April to September. NO2 air quality standard will be achieved by reducing vehicle NOx emission to post-new long-term regulation level. The analytical method was verified by using our developed simulation system, which consists of micro traffic flow analyzer and CFD-based, unsteady-state diffusion with chemical reaction solver.

Vehicle thermal protection is an important aspect of the overall vehicle development process. It involves optimizing the exhaust system routing and designing heat shields to protect various components that are in near proximity to the exhaust system. Reduced time to market necessitates an efficient process for thermal protection development. A robust procedure that utilizes state of the art CFD simulation techniques proactively during the design phase is described. Simulation allows for early detection of thermal issues and development of countermeasures several months before prototype vehicles are built. Physical testing is only used to verify the thermal protection package rather than to develop heat shields. The new procedure reduces the number of physical tests and results in a robust, efficient methodology.

Knock in spark-ignition (SI) engines has been a subject of many research efforts and its relationship with high efficiency operating conditions keeps it a contemporary issue as engine technologies push classical limits. Despite this long history of research, literature is lacking coherent and generalized descriptions of how knock is affected by changes in the full cylinder temperature field, residence time (engine speed), and air/fuel ratio. In this work, two dimensionless numbers are applied to fully 3D SI conditions. First, the characteristic time of autoignition (ignition delay) is compared against the characteristic time of end-gas deflagration, which was used to predict knocking propensity. Second, the temperature gradient of the end-gas is compared against a critical detonation-based temperature gradient, which predicts the knock intensity.

High frequency wind noise caused by turbulent flow around the front pillars of a vehicle is an important factor for customer perception of ride comfort. In order to reduce undesirable interior wind noise during vehicle development process, a calculation and visualization method for exterior wind noise with an acceptable computational cost and adequate accuracy is required. In this paper an index for prediction of the strength of exterior wind noise, referred to as Exterior Noise Power (ENP), is developed based on an assumption that the acoustic power of exterior wind noise can be approximated by the far field acoustic power radiated from vehicle surface. Using the well-known Curle’s equation, ENP can be represented as a surface integral of an acoustic intensity distribution, referred to as Exterior Noise Power Distribution (ENPD). ENPD is estimated from turbulent surface pressure fluctuation and mean convective velocity in the vicinity of the vehicle surface.