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One of the remaining challenges in the simulation of the aerodynamics of ground vehicles is the modeling of the airflows around the spinning tires and wheels of the vehicle. As in most advances in the development of simulation capabilities, it is the lack of appropriately detailed and accurate experimental data with which to correlate that holds back the advance of the technology. The flow around the wheels and tires and their interfaces with the vehicle body and the ground is a critical area for the development of automobiles and trucks, not just for aerodynamic forces and moments, and their result on fuel economy and vehicle handling and performance, but also for the airflows and pressures that affect brake cooling, engine cooling airflows, water spray management etc.

Numerical simulation of aerodynamics for vehicle development is used to meet a wide range of performance targets, including aerodynamic drag for fuel efficiency, cooling flow rates, and aerodynamic lift for vehicle handling. The aerodynamic flow field can also be used to compute the advection of small particles such as water droplets, dust, dirt, sand, etc., released into the flow domain, including the effects of mass, gravity, and the forces acting on the particles by the airflow. Previous efforts in this topic have considered the water sprays ejected by rotating wheels when driving on a wet road. The road spray carries dirt particles and can obscure the side and rear glazing. In this study, road sprays are considered in which the effects of additional water droplets resulting from splashing and dripping of particles from the wheel house and rear under body are added to help understand the patterns of dirt film accumulation on the side glass and rear glass.

An important metric in the vehicle brake design process, the cool-down time for a brake disk, strongly influences the durability and reliability of brakes. However, the brake cool-down time is a function of many vehicle and chassis factors, making it time consuming and expensive to evaluate and optimize in hardware testing. In this study, we investigate an alternative approach to hardware testing for evaluating brake design cool-down time by implementing a CFD (Computational Fluid Dynamics) simulation based methodology. The simulation cases were all compared with test data and good agreement was observed between test data and simulation over a wide range of design parameters. It is therefore demonstrated that accurate simulation is a promising new approach to the brake design process.

Brake disc materials are being utilised that have low noise/dust properties, but are sensitive to contamination by surface water. This drives large dust shields, making brake cooling increasingly difficult. However, brake cooling must be delivered without compromising aerodynamic drag and hence CO2 emissions targets. Given that front brake discs sit in a region of geometric, packaging and flow complexity optimization of their performance requires the analysis of thermal, aerodynamic and multi-phase flows. Some of the difficulties inherent in this task would be alleviated if the complete analysis could be performed in the same CAE environment: utilizing common models and the same solver technology. Hence the project described in this paper has sought to develop a CFD method that predicts the amount of contamination (water) that reaches the front brake discs, using a standard commercial code already exploited for both brake disc thermal and aerodynamics analysis.

Many critical thermal issues that occur in vehicles are uncovered only under more “thermally stressed” driving conditions that are transient in nature such as abruptly changing vehicle speed or turning off fan and engine. Therefore, for flow simulations to be useful in the vehicle design process, it is imperative that these simulations have the ability to accurately model long term transient thermal convection on full vehicles. Presented are simulations for a passenger vehicle driving at 60 kilometers per hour followed by a complete stop. The simulations were performed using a coupling between the flow and thermal solver and in the process, taking into account convection, conduction and radiation effects. Temperature predictions were made both under steady state conditions and during the key-off. Good agreement with the measurements was observed.

Thermal performance of a brake system is one of the key attributes in a new vehicle development process. Adequate brake cooling characteristics are part of the vehicle performance and safety requirements. The design of a new brake system, however, can be a complex task from a thermal engineering perspective, particularly because of complex interactions between the brake component and the rest of the vehicle. Frequently, the vehicle integration issues are the most serious challenges for brake engineers. There are considerations on how much heat should be dissipated from a single and/or consecutive braking events vs. how much cooling can be provided to the brake corner. Design issues such as where to direct the cooling air to how much flexibility is allowed while complying with other requirements from the studio and aero teams. For a brake engineer, the priority is to maximize cooling to the brake corner and prevent system failure.

Aerodynamic performance assessment of automotive shapes is typically performed in wind tunnels. However, with the rapid progress in computer hardware technology and the maturity and accuracy of Computational Fluid Dynamics (CFD) software packages, evaluation of the production-level automotive shapes using a digital process has become a reality. As the time to market shrinks, automakers are adopting a digital design process for vehicle development. This has elevated the accuracy requirements on the flow simulation software, so that it can be used effectively in the production environment. Evaluation of aerodynamic performance covers prediction of the aerodynamic coefficients such as drag, lift, side force and also lift balance between the front and rear axle. Drag prediction accuracy is important for meeting fuel efficiency targets, prediction of front and rear lifts as well as side force and yawing moment are crucial for high speed handling.

At SAIC-GM-Wuling (SGMW) the greenhouse wind noise performance of their vehicles has gained a lot of attention in the development process. In order to evaluate and improve the noise quality of a newly developed SUV a digital simulation based process has been employed during the early stage of the design. CFD simulation was used for obtaining the flow induced exterior noise sources. Performance metrics for the quality were based on interior noise levels which were calculated from the exterior sources using a SEA approach for the noise transmission through the glass panels and propagation to the driver’s or passenger’s head space. Detailed analysis of the CFD results allowed to identify noise sources and related flow structures. Based on this analysis, design modifications were then applied and tested in a sequential iterative process. As a result an improvement of more than 2 dB in overall sound pressure level could be achieved.

Design and evaluation of construction equipments and vehicles in the construction industry constitute a very important but expensive and time consuming part of the engineering process on account of large number of variants of prototypes and low production volumes associated with each variant. In this article, we investigate an alternative approach to the hardware testing based design process by implementing a Computational Fluid Dynamics (CFD) simulation based methodology that has the potential to reduce the cost and time of the entire design process. The simulation results were compared with test data and good agreement was observed between test data and simulation.

Trucks can carry heavy load and when applying the brakes during for example a mountain downhill or for an abrupt stop, the brake temperatures can rise significantly. Elevated temperatures in the drum brake region can reduce the braking efficiency or can even cause the brake system to fail, catch fire or even break. It therefore needs to be designed such to be able to transfer the heat out of its system by convection, conduction and/or radiation. All three heat transfer modes play an important role since the drum brakes of trucks are not much exposed to external airflow, a significant difference from disk brakes of passenger cars analyzed in previous studies. This makes it a complex heat transfer problem which is not easy to understand. Numerical methods provide insight by visualization of the different heat transfer modes. Presented is a numerical method that simulates the transient heat transfer of a truck drum brake system cooldown at constant driving speed.

The validation of vehicle aerodynamic simulation results to wind tunnel test results and simulation accuracy improvement attract considerable attention of many automotive manufacturers. In order to improve the simulation accuracy, a simulation model of the ground effects simulation system of the aerodynamic wind tunnel of the Shanghai Automotive Wind Tunnel Center was built. The model includes the scoop, the distributed suction, the tangential blowing, the moving belt and the wheel belts. The simulated boundary layer profile and the pressure distribution agree well with test results. The baseline model and multiple design changes of the new Buick Excelle GT are simulated. The simulation results agree very well with test results.

Pickup trucks are designed with a taller ride height and a larger tire envelope compared to other vehicle types given the duty cycle and environment they operate in. These differences play an important role in the flow field around spinning wheels and tires and their interactions with the vehicle body. From an aerodynamics perspective, understanding and managing this flow field are critical for drag reduction, wheel design, and brake cooling. Furthermore, the validation of numerical simulation methodology is essential for a systematic approach to aerodynamically efficient wheel design as a standard practice of vehicle design. This paper presents a correlation the near-wheel flow field for both front and rear spinning wheels with two different wheel designs for a Ram Quad Cab pick-up truck with moving ground. Twelve-hole probe experimental data obtained in a wind tunnel with a full width belt system are compared to the predictions of numerical simulations.

Aerodynamic efficiency plays an increasingly important role in the automotive industry, as the push for increased fuel economy becomes a larger factor in the engineering and design process. Longitudinal drag is used as the primary measure of aerodynamic performance, usually cited as the coefficient of drag (CD). This drag is created mostly by the body shape of the vehicle, but the wheel and tire system also contributes a significant portion. In addition to the longitudinal drag created by the body and wheels, rotational drag can add an appreciable amount of aerodynamic resistance to the vehicle as well. Reducing power consumption is an especially vital aspect in electric vehicle (EV) design. As the world's first luxury electric sedan, the Tesla Model S combines a premium driving experience with an electric drivetrain package that allows for unique solutions to many vehicle subsystems.