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Technical Paper

DIGITAL PHYSICS™ Analysis of the Morel Body in Ground Proximity

1997-02-24
970139
Presented is a study of the air flow over the Morel body [1] in ground proximity which was obtained using a discrete particle method, referred to as DIGITAL PHYSICS. The results were computed at several back-light angles and will be compared to experimental observations. Separation and reattachment along the angled section at a back-light angle of 30 degrees, and complete separation at 35 degrees, were both accurately predicted.
Technical Paper

Aerodynamic Simulation of a Standalone Rotating Treaded Tire

2017-03-28
2017-01-1551
The aerodynamics of a rotating tire can contribute up to a third of the overall aerodynamic force on the vehicle. The flow around a rotating tire is very complex and is often affected by smallest tire features. Accurate prediction of vehicle aerodynamics therefore requires modeling of tire rotation including all geometry details. Increased simulation accuracy is motivated by the needs emanating from stricter new regulations. For example, the upcoming Worldwide harmonized Light vehicles Test Procedures (WLTP) will place more emphasis on vehicle performance at higher speeds. The reason for this is to bring the certified vehicle characteristics closer to the real-world performance. In addition, WLTP will require reporting of CO2 emissions for all vehicle derivatives, including all possible wheel and tire variants. Since the number of possible derivatives can run into the hundreds for most models, their evaluation in wind tunnels might not be practically possible.
Journal Article

Further Analyses on Prediction of Automotive Spinning Wheel Flowfield with Full Width Moving Belt Wind Tunnel Results

2017-03-28
2017-01-1519
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.
Journal Article

Validation of Aerodynamic Simulation and Wind Tunnel Test of the New Buick Excelle GT

2017-03-28
2017-01-1512
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.
Journal Article

Numerical Investigation of Features Affecting Rear and Side Body Soiling

2017-03-28
2017-01-1543
Vehicle rear and side body soiling has been a concern since the earliest cars. Traditionally, soiling has been seen to be less importance than vehicle aerodynamics and acoustics. However, increased reliance on sensors and cameras to assist the driver means that there are more surfaces of the vehicle that must be kept clean. Failure to take this into consideration means risking low customer satisfaction with new features. This is because they are likely to fail under normal operating conditions and require constant cleaning. This paper numerically investigates features known to have an influence on side and rear face soiling with a demonstration vehicle. These changes include rim design, diffuser strakes and diffuser sharpening. While an exhaustive investigation of these features is beyond the scope of this study, examples of each feature will be considered.
Journal Article

Accurate Fuel Economy Prediction via a Realistic Wind Averaged Drag Coefficient

2017-03-28
2017-01-1535
The ultimate goal for vehicle aerodynamicists is to develop vehicles that perform well on the road under real-world conditions. One of the most important metrics to evaluate vehicle performance is the drag coefficient. However, vehicle development today is performed mostly under controlled settings using wind tunnels and computational fluid dynamics (CFD) with artificially uniform upstream conditions, neglecting real-world effects due to road turbulence from wind and other vehicles. Thus, the drag coefficients computed with these methods might not be representative of the real performance of the car on the road. This might ultimately lead engineers to develop design solutions and aerodynamic devices which, while performing well in idealized conditions, do not perform well on the road. For this reason, it is important to assess the vehicle’s drag as seen in real-world environments. An effort in this direction is represented by using the wind-averaged drag.
Technical Paper

Prediction of Charge Air Cooler Performance in a Racing Drive Cycle by 1D-3D Coupling

2018-04-03
2018-01-0781
Charge air temperature needs to be kept low for optimum engine operation. If charge air temperature is too high, engine performance reduction strategies are invoked to protect engines by limiting torque available to drivers. A 1D-3D coupling simulation methodology is developed to accurately predict internal air temperature after charge air cooler (CAC) during a racing drive cycle. The 3D flow simulation is used to characterize external air flow before CAC in steady-state cases. Then, interpolated 3D simulation results between steady operating points are used as transient external air boundary conditions in front of CAC in a 1D system model. 3D flow simulation is also used to predict internal flow rate ratio between CAC tubes. Finally, an 1D system model is used to predict time-trace of charge air temperature at CAC internal outlet during the racing drive cycle. The simulation results show that prediction errors are within 5 degrees for charge air temperature at internal outlets.
Technical Paper

Update on A-Pillar Overflow Simulation

2018-04-03
2018-01-0717
The management of surface water flows driven from the wind screen by the action of wipers and aerodynamic shear is a growing challenge for automotive manufacturers. Pressure to remove traditional vehicle features, such as A-Pillar steps for aesthetic, aeroacoustic and aerodynamic reasons increases the likelihood that surface water may be convected over the A-Pillar and onto the front side glass where it can compromise drivers’ vision. The ability to predict where and under which conditions the A-Pillar will be breached is important for making correct design decisions. The use of numerical simulation in this context is desirable, as experimental testing relies on the use of aerodynamics test properties which will not be fully representative, or late-stage prototypes, making it difficult and costly to correct issues. This paper provides an update on the ability of simulation to predict A-Pillar overflow, comparing physical and numerical results for a test vehicle.
Technical Paper

Evaluation and Improvement of Greenhouse Wind Noise of a SGMW SUV using Simulation Driven Design

2018-04-03
2018-01-0737
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.
Technical Paper

Long Term Transient Cooling of Heavy Vehicle Cabin Compartments

2010-10-05
2010-01-2018
A newly developed simulation methodology for a long term, transient tractor cabin cool-down is presented in this paper. The air flow was simulated using a Lattice-Boltzmann Equation (LBE) based 3-dimensional flow solver. The conduction and radiation effects on the solid parts as well as the average cabin air temperature evolution were solved by the thermal solver, which also includes a human comfort model. The simulation results were compared with the measured experimental test data and good agreement was observed validating the developed simulation approach. The developed methodology can be applied to all other ground vehicles cabin comfort applications.
Technical Paper

Aerodynamic Study of a Production Tractor Trailer Combination using Simulation and Wind Tunnel Methods

2010-10-05
2010-01-2040
The importance of fuel economy and emission standards has increased rapidly with high fuel costs and new environmental regulations. This requires analysis techniques capable of designing the next generation long-haul truck to improve both fuel efficiency and cooling. In particular, it is important to have a predictive design tool to assess how exterior design changes impact aerodynamic performance. This study evaluates the use of a Lattice Boltzmann based numerical simulation and the National Research Council (NRC) Canada's wind tunnel to assess aerodynamic drag on a production Volvo VNL tractor-trailer combination. Comparisons are made between the wind tunnel and simulation to understand the influence of wind tunnel conditions on truck aerodynamic performance. The production VNL testing includes a full range of yaw angles to demonstrate the influence of cross wind on aerodynamic drag.
Technical Paper

Optimization of Aerodynamics and Engine Cooling Performance of a JMC Mid-Size Truck using Simulation

2010-10-05
2010-01-2032
The engineering process in the development of commercial vehicles is facing more and more stringent emission regulations while at the same time the market demands for better performance but with lower fuel consumption and higher reliability. Respective targets require better utilization of existing or even higher engine cooling capacity and optimization of aerodynamic performance for reduced drag. In order to aid on achieving both goals, special attention should be paid on understanding both external and under hood flow structures. This paper describes an optimization study for reducing aerodynamic drag and increasing engine cooling performance conducted on a Light Truck at Jiangling Motors Corporation (JMC). The approach is using simulation based on a LBM solver coupled with a heat exchanger model. Such methodology was used to predict both aerodynamic and cooling characteristics and help highlighting potential areas for improvement.
Technical Paper

Hybrid Technique for Underbody Noise Transmission of Wind Noise

2011-05-17
2011-01-1700
Wind noise has become an important indicator for passenger automobile quality. Several transmission paths can be related to different parts of the vehicle exterior. While the greenhouse (side glasses, windshield, seals & others) often dominates the interior noise level above 500 Hz, the contribution coming from the underbody area usually dominates the interior noise spectrum at lower frequencies. This paper describes a framework of numerical tools which is capable of determining realistic underbody turbulent and acoustic loads being generated for typical driving conditions, as well as performing the noise transmission through underbody panels and the propagation of sound to the drivers ear location.
Technical Paper

A Computational Approach to Evaluate the Vehicle Interior Noise from Greenhouse Wind Noise Sources - Part II

2011-05-17
2011-01-1620
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 mainly 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.
Technical Paper

Lattice Boltzmann Simulations of the Unsteady Flow Behind the Ahmed Body

2008-04-14
2008-01-0740
The Ahmed body is a simplified vehicle geometry that results in flow features representative of those found at the rear of most passenger vehicles. By adjusting the rear slant angle, separation can take place at the sharp corner, on the rear slant panel, or not at all. Accurate prediction of the separation and reattachment of the flow is essential in predicting the correct drag trends. This separation and reattachment is known to be a highly unsteady phenomenon. The objective of this study is to evaluate the ability of a lattice Boltzmann based CFD code to predict the correct drag trends and flow structures for the Ahmed body at varying rear slant angles. Component and total drag values show excellent agreement with the original experiments of Ahmed over a wide range of rear slant angles (5 to 35 degrees).
Journal Article

The Effects of Detailed Tire Geometry on Automobile Aerodynamics - a CFD Correlation Study in Static Conditions

2009-04-20
2009-01-0777
A correlation study was performed between static wind tunnel testing and computational fluid dynamics (CFD) for a small hatchback vehicle, with the intent of evaluating a variety of different wheel and tire designs for aerodynamic forces. This was the first step of a broader study to develop a tool for assessing wheel and tire designs with real world (rolling road) conditions. It was discovered that better correlation could be achieved when actual tire scan data was used versus traditional smooth (CAD) tire geometry. This paper details the process involved in achieving the best correlation of the CFD prediction with experimental results, and describes the steps taken to include the most accurate geometry possible, including photogrammetry scans of an actual tire that was tested, and the level of meshing detail utilized to capture the fluid effects of the tire detail.
Journal Article

Response of a Prototype Truck Hood to Transient Aerodynamic Loading

2009-04-20
2009-01-1156
A study was performed to determine the fluid structure interaction (FSI) for a prototype truck hood for transient aerodynamic loads. The growing need to make vehicle panels lighter to enhance the fuel economy of vehicles has made hood panels more prone to deformation and vibration from aerodynamic loads. Moreover, as global pedestrian crash standards become more stringent to provide safer front end designs to minimize injuries to head and leg, automotive manufacturers are being required to design flexible hoods that crush significantly more than the present designs to absorb the crash energy better. These flexible designs lead to potentially undesirable deformations and/or vibration behavior of the hood at typical highway speeds.
Journal Article

Simulation of Cooling Airflow and Surface Temperature of a Midsize Truck

2009-10-06
2009-01-2894
This paper presents a simulation of the cooling airflow and surface temperatures of a midsize truck. The simulation uses full detailed geometry of the truck. Performance of the under-hood cooling airflow is analyzed and potential design changes leading to better cooling airflow are highlighted. Surface temperature over certain under-hood part is studied. Possible optimizations using various material and configurations are proposed. It is shown that the presented simulation approach provides valuable information to evaluate cooling system and thermal protection performance. Fast design iterations can be achieved using this approach.
Technical Paper

HVAC Blower Aeroacoustic Predictions

2013-04-08
2013-01-1001
In recent years, vehicle cabin quietness takes a growing importance particularly related to the emergence of hybrid and electric vehicles and “Idle Stop system” vehicles. Demand for quieter car air-conditioner systems is increasingly important also, especially the reduction of the flow-induced noise from the HVAC. In HVAC systems, the rotating blower is one of the main noise sources and the digital solution for predicting and analyzing the blower aeroacoustic noise in the early stage of design is needed for developing a quieter blower. The target of this study is to develop and to validate a flow-induced noise predictive tool for a HVAC blower and to analyze the noise source. In this paper, a low-dissipation, transient, compressible CFD/CAA approach based on the Lattice Boltzmann Method (LBM) is used to predict simultaneously the flow and aeroacoustic radiation of two production blowers.
Journal Article

Simulation of Rear and Body Side Vehicle Soiling by Road Sprays Using Transient Particle Tracking

2013-04-08
2013-01-1256
Numerical simulations have proven to be effective tools for the aerodynamic design of vehicles, helping to reduce drag, improve cooling flows, and balance aerodynamic lift. Aeroacoustic simulations can also be performed; these can give guidance on how design changes may affect the noise level within the cabin. However, later in the development process it may be discovered that soiling management issues, for example, necessitate design changes. These may have adverse consequences for noise or require extra expense in the form of technological counter-measures (i.e. hydrophobic glass). Performing soiling simulations can allow these potential issues to be addressed earlier in the design process. One of the areas where simulation can be particularly useful is in the prediction of soiling due to wheel spray.
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