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The detailed design process of the diffuser for a Formula one racer is described. It begins with the study of overall aerodynamic performance and follows the basic function of the diffuser. And then forms the strategy for such a diffuser which should perform the maximum downforce. Then is the detailed analysis of diffuser by two different methods of development. The small-scaled wind tunnel data is presented, together with the CFD analysis, describing the major consideration in using these two developing methods and demonstrating the major influence for the diffuser design.

Computational fluid dynamics (CFD) was used to simulate the flow field over a pickup truck. The simulation was based on a transient state formulation and the focus of the simulation was to assess the capabilities of the current RSM (Reynolds Stresses Model) in CFD tools for vehicle aerodynamic development for pickup trucks. Detailed comparisons were made between the CFD simulations and the existing experiments for a generic pickup truck. It was found that the flow structures obtained from the CFD calculations are very similar to the corresponding measured mean flows. Furthermore, the surface pressure distributions are captured reasonably well by the CFD analysis. Comparison for computational results was carried out for both linear Pressure Strain model (Launder, Reece and Rodi, 1978) and Quadratic Pressure Strain model (Speziale, Sarkar and Gatski, 1991). The CFD results of Linear and Quadratic RSM are very close to the test data.

CFD method for the calculation of flow rate and air re-circulation at vehicle idle conditions is described. A small velocity is added to the ambient airflow in order to improve the numerical stability. The flow rate passing through the heat exchangers is insensitive to the ambient velocity, since the flow rate is largely determined by the fan operation. The air re-circulation, however, is quite sensitive to the ambient air velocity. The ambient velocity of U=-1m/s was found to be the more critical case, and is recommended for the air re-circulation analysis. The CFD analysis can also lead to design modifications improving the air re-circulation.

Effects of the wind tunnel blockage in a closed-wall wind tunnel were investigated using computational fluid dynamics (CFD). Flow over three generic vehicle models representing a passenger sedan, a sports utility vehicle (SUV), and a pickup truck was solved. The models were placed in a baseline virtual wind tunnel as well as four additional virtual wind tunnels, each with different size cross-sections, providing different levels of wind tunnel blockage. For each vehicle model, the CFD analysis produced an aerodynamic drag coefficient for the vehicle at the blockage free condition as well as the blockage effect increment for the baseline wind tunnel. A CFD based blockage correction method is proposed. Comparisons of this method to some existing blockage correction methods for closed-wall wind tunnel are also presented.

Effects of the pressure gradient in the wind tunnel test section on vehicle aerodynamic drag were investigated using computational fluid dynamics (CFD). The numerical study was used to obtain the aerodynamic drag of several vehicles in two virtual wind tunnels, one with a zero pressure gradient and another with a nonzero (but small) pressure gradient. A comparison of the vehicle aerodynamic drags in these two virtual wind tunnels, and investigation of the physical mechanisms causing these differences, have led to two correction formulas. These formulas can be used to correct for the pressure gradient effect on vehicle aerodynamic drag measurement in a wind tunnel that has a nonzero pressure gradient. In the first formula, the correction is given explicitly in terms of known variables. The correction is 80% accurate for passenger car, sports car, sports utility vehicle (SUV), and is 70% accurate for pickup truck.

The concept of condenser, fan, and radiator power train cooling module (CFRM) was further evaluated via three-dimensional computational fluid dynamics (CFD) studies in the present paper for vehicle at idle conditions. The analysis shows that the CFRM configuration was more prone to the problem of front-end air re-circulation as compared with the conventional condenser, radiator, and fan power train cooling module (CRFM). The enhanced front-end air re-circulation leads to a higher air temperature passing through the condenser. The higher air temperature, left unimproved, could render the vehicle air conditioning (AC) unit ineffective. The analysis also shows that the front-end air re-circulation can be reduced with an added sealing between the CFRM package and the front of the vehicle, making the CFRM package acceptable at the vehicle idle conditions.

Beamforming techniques are widely used today in aeroacoustic wind tunnels to identify wind noise sources generated by interaction between incoming flow and the test object. In this study, a planar spiral microphone array with 120 channels was set out-of-flow at 1:1 aeroacoustic wind tunnel of Shanghai Automotive Wind Tunnel Center (SAWTC) to test exterior wind noise sources of a production car. Simultaneously, 2 reference microphones were set in vehicle interior to record potential sound source signal near the left side view mirror triangle and the signal of driver’s ear position synchronously. In addition, a spherical array with 48 channels was set inside the vehicle to identify interior noise sources synchronously as well. With different correlation methods and an advanced algorithm CLEAN-SC, the ranking of contributions of vehicle exterior wind noise sources to interested interior noise locations was accomplished.

By means of particle image velocimetry(PIV) measurements, this paper uses vortex identification algorithms to find and analyze the coherent structures in the shear layer region of a 1:15 scaled 3/4 open jet automotive wind tunnel with a high Reynolds number(about 106), referring to SAWTC’s AAWT. The proper orthogonal decomposition(POD) is used to process the PIV experimental data to reconstruct the velocity fields. Based on the vortex identification functions, the locations of the center, the rotation direction and the radius of vortex can be computed. Furthermore, this paper uses the statistical method to study the regularities of distribution of these vortexes in a two-dimensional plane, and identify the vortex pairing process in the shear layer region. This paper also chooses different vortex identification algorithms to find the most accurate and suitable algorithms.

Wheel Aerodynamics is an important part of vehicle aerodynamics. The wheels can notably influence the total aerodynamic drag, lift and ventilation drag of vehicles. In order to simulate the real on-road condition of driving cars, the moving ground and wheel rotation is of major importance in CFD. However, the wheel rotation condition is difficult to be represented exactly, so this is still a critical topic which needs to be worked on. In this paper, a study, which focuses on two types of cars: a fastback sedan and a notchback DrivAer, is conducted. Comparing three different wheel rotating simulation methods: steady Moving wall, MRF and unsteady Sliding Mesh, the effects of different methods for the numerical simulation of vehicle aerodynamics are revealed. Discrepancies of aerodynamic forces between the methods are discussed as well as the flow field, and the simulation results are also compared with published experimental data for validation.

The air passages of a plenum are investigated with Computational Fluid Dynamics (CFD) simulations. The objectives of the simulations are to examine the pressure drop between inlet (windshield base) and outlet (blower inlet), the water intrusion quantity into the HVAC module, and the velocity profile and flow rate at the outlet. An initial analysis relies on a two dimensional mesh around the chimney area. The velocity distribution at the outlet and the pressure drop (between inlet and outlet) are compared between a baseline design and a design with guide vanes. A more detailed analysis is conducted with a three dimensional mesh, to examine designs with different baffle/vane locations and inlet openings. Designs with baffles were found to reduce the water quantity entering the HVAC module. However, the pressure drop increased because the flow paths were choked.

Component operating temperatures affect both the reliability and performance of automotive alternators. It is desirable to keep the rectifier bridge and regulator temperatures below 175 C because of the semiconductors contained in this area. At temperatures greater than this, expected lifespans have been observed to decay exponentially [1]. The air flow field surrounding an alternator and component temperature fields were investigated with Computational Fluid Dynamics (CFD) simulations. The objectives of the simulations were to examine the velocity field for the flow passage and the temperature fields for the components. Design proposals have been made to improve the air flow and to reduce the operating temperature. An initial investigation was performed by setting an alternator in a test configuration and applying the appropriate heat generation for each component. The high temperatures in the alternator components occurred in the stator and the rectifier.

Air flow around the front brake assembly was computed using STAR-CD version 2.300, a commercial Computational Fluid Dynamics (CFD) code in order to explore the possibility of using this technique as a design tool. The primary objective in a brake corner assembly design is to maximize air cooling of the brake rotor. It is a very challenging task that requires experiments that are both expensive and time consuming in order to evaluate and optimize the various design possibilities. In this study, it is demonstrated that the design procedure can be shortened and made less expensive and be accurate using flow simulations. Accordingly, the air flow around the front brake assembly was computed for three different designs and for three different car speeds. A computational mesh was built using PROSTAR, the STAR-CD pre and post-processor. The three-dimensional mesh had almost 900,000 cells. All geometrical components were modelled.

The air passages in tailpipe end geometries are investigated with Computational Fluid Dynamics (CFD) simulations. The overall objective of the simulations is to select an optimum design which has a mimimum capacity for noise generation. This is accomplished by comparing pressure drops between inlet and outlet and by examining the turbulent kinetic energy levels in the flow domain. Two designs for the tailpipe end geometries were evaluated. It was found that turbulent kinetic energy levels and pressure drops were lowest in a single pipe design which had relatively smooth internal contours. We conclude that the present CFD approach can provide useful design information in a short time frame (a few weeks) for exhaust pipe tip geometries for reduced pressure drop and noise generation.

The computational fluid dynamics (CFD) based wind tunnel blockage correction method proposed in [1] was extended in the present study to production vehicles with detailed underhood and underbody components, fascia and grills. Three different types of vehicles (sedan, SUV, and pickup truck) were considered in the study. While the previous CFD based wind tunnel blockage correction method was for vehicle aerodynamic drag, the blockage effect on vehicle cooling airflow is also included in the present study, and a CFD based blockage correction method for vehicle cooling airflow is proposed. Comparisons were made between the blockage effects for the production vehicles and the blockage effects for the generic vehicles.

Computational fluid dynamics (CFD) was used to simulate the flow field over a pickup truck. The simulation was based on a steady state formulation and the focus of the simulation was to assess the capabilities of the currently used CFD tools for vehicle aerodynamic development for pickup trucks. Detailed comparisons were made between the CFD simulations and the existing experiments for a generic pickup truck. It was found that the flow structures obtained from the CFD calculations are very similar to the corresponding measured mean flows. Furthermore, the surface pressure distributions are captured reasonably well by the CFD analysis. Comparison for aerodynamic drags was carried out for both the generic pickup truck and a production pickup truck. Both the simulations and the measurements show the same trends for the drag as the vehicle geometry changes, This suggests that the steady state CFD simulation can be used to aid the aerodynamic development of pickup trucks.

The effect of jet geometry on flow, heat transfer and defrosting characteristics was numerically investigated for elliptic and rectangular impinging jets on an automobile windshield. Initially, various turbulence models within the commercial computational fluid dynamics (CFD) package FLUENT were employed and validated for a single jet, and the results indicated that the impinging jet heat transfer was more accurately predicted by the SST k -ω turbulence model, which was then utilized for this study. The aspect ratios (AR) of elliptic and rectangular jets were respectively 0.5, 1.0, and 2.0, with jet-to-target spacing h/d=2, 4 and jet-to-jet spacing c/d=4, and all those situations were numerically analyzed with the same air mass flow and jet open area. It was observed that the heat transfer coefficient and defrosting performance of the inclined windshield were significantly affected by the shape of the jet, and the best results were obtained with the elliptic jet arrangements.

CFD (Computational Fluid Dynamics) has been used to analyze vehicle air flow. In cross wind conditions an asymmetrical flow field around the vehicle is present. Under these circumstances, in addition to the forces present with symmetric air flow (drag and lift forces and pitching moment), side forces and moments (rolling and yawing) occur. Issues related to fuel economy, driveability, sealing effects (caused by suction exerted on the door), structural integrity (sun roof, spoiler), water management (rain deposit), and dirt deposit (shear stress) have been investigated. Due to the software developments and computer hardware improvements, results can be obtained within a reasonable time frame with excellent accuracy (both geometry and analytical solution). The flow velocity, streamlines, pressure field, and component forces can be extracted from the analysis results through visualization to identify potential improvement areas.

Based on a 1:15 scaled 3/4 open jet automotive wind tunnel, this paper studies the effect of vortex generator on the buffeting phenomenon. The mean velocity, static pressure gradient, turbulent intensity as well as frequencies of fluctuant velocities have been explored experimentally with and without vortex generator. It shows that the less protruding vortex generator could control the buffeting phenomenon and improve the flow quality. Furthermore, the unsteady coherent structures in the jet shear layer have been visualized and analyzed by Detached-eddy simulation (DES). The vortex-ring pairing process is identified in the shear layer along with obvious frequency characteristics and velocity fluctuations. The vortex generator can postpone and restrain this vortex-ring pairing process, then reducing the velocity fluctuations.