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This study was initiated to evaluate the thermal characteristics of a vehicle underbody using math-based computational fluid dynamics (CFD) simulation based on 3-D configuration. Simulations without heat shields were carried out for different vehicle operating conditions which placed several areas at risk of exceeding their thermal design limits. Subsequently, simulations with several heat shield designs were performed. Results show that areas at risk without shields are well within thermal design limits when shielded. Part of the CFD simulation results were compared with experimental data, with reasonable correlation. The CFD approach can provide useful design information in a very short time frame.

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.

In the present work computational fluid dynamics (CFD) simulations of the flow field around a generic tractor-trailer truck are presented and compared with corresponding experimental measurements. A generic truck model was considered which is a detailed 1/8th scale replica of a Class-8 tractor-trailer truck. It contained a number of details such as bumpers, underbody, tractor chassis, wheels, and axles. CFD simulations were conducted with wind incident on the vehicle at 0 and 6 degree yaw. Two different meshing strategies (tet-dominant and hex-dominant) and three different turbulence models (Realizable k-ε, RNG k-ε, and DES) are considered. In the first meshing strategy an unstructured tetrahedral mesh was created over a large region surrounding the vehicle and in its wake. In the second strategy the mesh was predominantly hexahedral except for a few narrow regions around the front end and the underbody which were meshed with tetrahedral cells owing to complex topology.

Swirl/tumble are rotational flow inside the combustion chamber. Fluent Computational Fluid Dynamics (CFD) software has been successfully used to simulate engine swirl and tumble flow. Two mesh approaches are possible within Fluent software to calculate transient engine swirl and tumble. One approach uses hybrid mesh with remeshing, while the other approach uses hex/wedge mesh with layering. The hybrid method employs tetrahedral remeshing, and is easier to set up compared to hex/wedge method for which only layering is used. Being easier to use, the hybrid method raises some concerns about result accuracy due to higher numerical diffusion associated with tet elements compared to the corresponding hex/wedge elements used for layering approach. This paper examines the two mesh approaches in terms of result accuracy for two engines, one SI and one diesel. The results are compared with PIV data for the SI engine.

In order to evaluate the impact of emission of pollutants on the environment, it has become increasingly important that the dispersion of pollutants be predicted accurately. Recently, USEPA has proposed stringent guidelines for regulating the diesel exhaust emissions, specifically, NOx, COx, SOx, and particulate matter (PM) due to green house effect, and ozone depletion. Modeling pollutant transport in the atmospheric environment is complicated by the fact that there are many turbulent mixing time scales and spatial scales present which directly influence the dispersion of the plume. The traditional approach to predicting pollutant dispersion in the atmosphere is the use of Gaussian plume models. The Gaussian models are based on a steady state assumption, and they require the flow to be in a homogeneous and stationary turbulence state.

A gasoline direct injection fuel spray was observed using a fired, optical access, square cross-section single cylinder research engine and high-speed video imaging. Spray interaction with the piston is described qualitatively, and the results are compared with Computational Fluid Dynamics (CFD) simulation results using KIVA-3V version 2. CFD simulations predicted that within the operating window for stratified charge operation, between 1% and 4% of the injected fuel would remain on the piston as a liquid film, dependent primarily on piston temperature. The experimental results support the CFD simulations qualitatively, but the amount of fuel film remaining on the piston appears to be under-predicted. High-speed video footage shows a vigorous spray impingement on the piston crown, resulting in vapor production.

A numerical method of predicting aeroacoustic performance of HVAC ducts is presented here. The method comprises of two steps. First, the steady state flow structure inside a duct is simulated using computational fluid dynamics (CFD). A k-epsilon based turbulence model is used. In the second step broadband noise source models are used to estimate the sound power generation within the duct. In particular, models estimating dipole and quadrupole sound source strengths are studied. A baseline generic duct geometry was studied with 3 additional design variations. The loudness rankings of these three designs were determined numerically. Simultaneously, the sound generated by these three designs was measured on a flow bench with a microphone kept downstream of the duct outlet. The numerically predicted loudness rankings were compared with experimentally determined rankings and the two are found to be in agreement, thus validating the numerical method.

The recent development of a new vane-type pump for power steering applications involved paying special attention to the fluid flow dynamics within the pump casing, especially in the flow control or supercharge region, where excess pump fluid flow is diverted to the intake region. Durability testing of initial designs revealed the presence of cavitation damage to the pump casing in the supercharging region. Subsequent Computational Fluid Dynamics (CFD) analyses as well as experimental Flow Visualization studies aided in resolving the cavitation-damage problem. The purpose of this paper is to describe the processes used in the CFD analyses and flow visualization studies. A two-dimensional (2D) convergence study was conducted to determine the CFD meshing requirements across the small orifice at the intersection of the flow-control valve and the supercharge port. An iterative procedure was employed to determine the operating position of the flow-control valve.

There is an increasing interest in transient thermal simulations of automotive brake systems. This paper presents a high-fidelity CFD tool for modeling complete braking cycles including both the deceleration and acceleration phases. During braking, this model applies the frictional heat at the interface on the contacting rotor and pad surfaces. Based on the conductive heat fluxes within the surrounding parts, the solver divides the frictional heat into energy fluxes entering the solid volumes of the rotor and the pad. The convective heat transfer between the surfaces of solid parts and the cooling airflow is simulated through conjugate heat transfer, and the discrete ordinates model captures the radiative heat exchange between solid surfaces. It is found that modeling the rotor rotation using the sliding mesh approach provides more realistic results than those obtained with the Multiple Reference Frames method.

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.

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.

A multiple reference frame (MRF) model was developed by Gosman [1] for the prediction of flow fields induced by impellers in mixing vessels. The simulation results using this approach agree with the test data reasonably well if certain conditions exist. Many CFD engineers have adopted this approach to simulate the fan performance for automotive powertrain cooling simulations [4]. This paper describes the authors' experience using the MRF model in truck fan simulations. For the fan performance studies with a plate shroud, CFD simulation results with different sizes of rotating zones were compared with the test data. Very good agreement between the CFD simulation and the test data with plate shroud can be achieved if a properly sized rotating zone is selected. For the fan performance studies with a real shroud, a simple piece of plywood was used to mimic the engine blockage and the MRF model with one fixed-size rotation zone was used for the CFD simulation.

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.

Computational fluid dynamics (CFD) simulations of the transient flow-field around a generic side view mirror shape are presented that provide insight into the wind noise generated by the mirror. The generic mirror shape consists of half a cylinder, 0.2 m in diameter and length, topped with a quarter of a sphere of the same diameter. The transient flow past the generic side view mirror is simulated using the commercial CFD code Fluent with the LES turbulence model. A flow velocity of 200 km/hr is considered which correspond to a Reynolds number of 7 × 105. Detailed velocity vectors and contour plots of the time-varying velocity and pressure fields are presented along cut-planes in the flow-field. Mean and transient pressure are also monitored at several points in the flow field and compared to corresponding experimentally data published in literature. The results are also compared with predictions made using the Ffowcs-Williams-Hawkins acoustic analogy.

Minor geometric features in the intake manifold airflow path with side-branch cavities are often responsible for unusual noise due to the complex air flow structure and its interaction with the internal acoustic field. Although airflow bench tests are faster to evaluate various alternate design geometries, understanding the mechanism of such noise generation is necessary for developing an effective design. A 2D computational fluid dynamics (CFD) simulation was performed on a baseline geometry, which produced a distinct whistle, and on a modified geometry, which suppressed the whistle. These 2D models were able to simulate the flow-acoustic coupling responsible for the whistle generation and hence clearly predicted the presence or the absence of a distinct whistle peak as observed in the experimental measurements.

Computational Fluid Dynamics (CFD) is frequently used to predict complex flow phenomena and assist in engine design and optimization. The scavenge process within a 2-stroke engine is key to engine performance especially in high performance racing applications. In this paper, FLUENT CFD code is used to simulate the scavenging process within a 125cc single cylinder racing engine. A variety of different port designs are simulated and scavenge characteristics compared and contrasted. The predicted CFD results are compared with measured scavenge data obtained from the QUB single-cycle scavenge rig. These results show good agreement and provide valuable insight into the effect of port design features on the scavenging process.

This paper presents a 3-D CFD modelling of flow and heterogeneous reactions in catalytic converters. The pressure and velocity fields in the catalytic converters are calculated by the state of the art modelling technique for the flow resistance of catalyst substrate. A surface reaction model is applied to predict the performance of a three-way Pt/Rh catalyst. A reaction mechanism with detailed catalytic surface reactions for the 3-way catalyst is applied. The novelty of this approach is the use of a surface chemistry solver coupled with a 3-D CFD code in the entire computational domain of the catalyst substrate that allows flow distribution for complex configurations to be accounted for. The concentrations of the gas species and the site species are obtained. A comparison between the simulation results and the experimental data of a three-way catalyst was made.

The front-end design process in the automotive industry today is time consuming and expensive. Although CFD (Computational Fluid Dynamics) modeling is helpful, many vehicle development tests in different wind tunnels are still required to balance the competing requirements of power train cooling, vehicle aerodynamics, climate control, styling, body structure, and product cost. For example, engine cooling and climate control heat exchangers require adequate airflow to achieve their performance. But, this airflow increases cooling drag and can compromise vehicle handling. Internal air deflectors (ducting) are often used to make the frontal opening more efficient and help prevent heat recirculation from the hot engine compartment to the A/C condenser at idle. But this increases product cost and can compromise underhood temperature. A more efficient and faster process is needed to support these trade-off discussions.

Multidimensional modeling of in-cylinder processes has traditionally relied upon comparison with experimentally determined gross quantities, such as swirl ratio or valve discharge coefficient. Recent experimental studies have focused on accurate in-cylinder measurement of quantities such as velocity fields, species concentration distributions and distributions or turbulent kinetic energy. Since the most important engine design parameters, including filling efficiency, flame stability and pollutant formation depend on the local flow field, the ability to accurately predict these details is a key requirement for successful application of computational fluid dynamics techniques to engine design.