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Technical Paper

The Immersed Boundary CFD Approach for Complex Aerodynamics Flow Predictions

Standard CFD methods require a mesh that fits the boundaries of the computational domain. For a complex geometry the generation of such a grid is time-consuming and often requires modifications to the model geometry. This paper evaluates the Immersed Boundary (IB) approach which does not require a boundary-conforming mesh and thus would speed up the process of the grid generation. In the IB approach the CAD surfaces (in Stereo Lithography -STL- format) are used directly and this eliminates the surface meshing phase and also mitigates the process of the CAD cleanup. A volume mesh, consisting of regular, locally refined, hexahedrals is generated in the computational domain, including inside the body. The cells are then classified as fluid, solid and interface cells using a simple ray-tracing scheme. Interface cells, correspond to regions that are partially fluid and are intersected by the boundary surfaces.
Technical Paper

Numerical Investigation of Road Vehicle Aerodynamics Using the Immersed Boundary RANS Approach

This paper describes the computational results of the flow field around two vehicle geometries using the Immersed Boundary (IB) technique in conjunction with a steady RANS CFD solver. The IB approach allows the computation of the flow around objects without requiring the grid lines to be aligned with the body surfaces. In the IB approach instead of specifying body boundary conditions, a body force is introduced in the governing equations to model the effect of the presence of an object on the flow. This approach reduces the time necessary for meshing and allows utilization of more efficient and fast CFD solvers. The simulations are carried out for an SUV and a pickup truck models at a Reynolds number of 8×105. Cartesian meshes (non-uniform) with local grid refinement are used to increase the resolution close to the boundaries. The simulation results are compared with the existing measurements in terms of surface pressures, velocity profiles, and drag coefficients.
Technical Paper

Multidimensional Port-and-in-Cylinder Flow Calculations and Flow Visualization Study in an Internal Combustion Engine with Different Intake Configurations

Multidimensional simulations of coupled intake port/valve and in-cylinder flow structures in a pancake-shape combustion chamber engine are reported. The engine calculations include moving piston, moving intake valve, and valve stem. Direct comparisons of three intake configurations for the same cylinder geometry are presented: (1) standard intake valve; (2) intake valve with high-swirl shroud orientation; and (3) intake valve with across-head shroud orientation. In order to verify the calculated results, qualitative flow visualization experiments were carried out for the same intake geometries during the induction process using a transient water analog. During the intake process the results of the multidimensional simulation agreed very well with the qualitative flow visualization experiments.
Technical Paper

International Congress and Exposition Detroit, Michigan February 24-28, 1986Measured Steady Flow Velocity Distributions Around a Valve/Seat Annulus

Measurements were made of the three velocity components at the exit plane of the intake valve from an internal combustion engine. The velocities were measured using hot-wire anemometry in a steady-flow rig, and an assessment was made of the effects of flow rate, valve lift, cylinder bore diameter, and inlet configuration on the velocity distribution around the intake valve. The results showed that over the range of flow rates tested, the normalized velocity profiles are independent of flow rate. At a fixed flow rate, the velocity profiles around the valve periphery are found to be strongly dependent on proximity to the cylinder head. Close to the cylinder head, the profiles are skewed but become more uniform as the distance from the cylinder head increases. In addition, the results indicate that the profiles are sensitive to the valve lift and to the proximity of the cylinder wall to the valve axis.
Technical Paper

Intake-Generated Swirl and Tumble Motions in a 4-Valve Engine with Various Intake Configurations-Flow Visualization and Particle Tracking Velocimetry

Flow visualization and particle tracking velocimetry (PTV) were used to study the in-cylinder flow field produced by a 4-valve engine head during the intake process. Several intake configurations were considered, and their effects on the in-cylinder flow structures were assessed. The engine head was mounted on a special single cylinder water analog for the in-cylinder flow visualization and PTV experiments. The results for this study indicate that the in-cylinder flow field during the induction process is comprised of several large scale vortical motions on different planes within the engine cylinder. These large scale fluid motions are, in most cases, stable and highly repeatable from cycle to cycle. No significant in-cylinder tumbling motion was observed in the engine with both intake valves operating. The only well-defined tumbling flow structure was observed with shrouded intake valve configurations.
Technical Paper

Experimental and Computational Study of Unsteady Wake Flow Behind a Bluff Body with a Drag Reduction Device

Simple devices have been shown to be capable of tailoring the flow field around a vehicle and reducing aerodynamic drag. An experimental and computational investigation of a drag reduction device for bluff bodies in ground proximity has been conducted. The main goal of the research is to gain a better understanding of the drag reduction mechanisms in bluff-body square-back geometries. In principle, the device modifies the flow field behind the test model by disturbing the shear layer. As a consequence, the closure of the wake is altered and reductions in aerodynamic drag of more than 20 percent are observed. We report unsteady base pressure, hot-wire velocity fluctuations and Particle Image Velocimetry (PIV) measurements of the near wake of the two models (baseline and the modified models). In addition, the flows around the two configurations are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with the V2F turbulence model.
Technical Paper

Experimental Investigation of the Flow Around a Generic SUV

The results of an experimental investigation of the flow in the near wake of a generic Sport Utility Vehicle (SUV) model are presented. The main goals of the study are to gain a better understanding of the external aerodynamics of SUVs, and to obtain a comprehensive experimental database that can be used as a benchmark to validate math-based CFD simulations for external aerodynamics. Data obtained in this study include the instantaneous and mean pressures, as well as mean velocities and turbulent quantities at various locations in the near wake. Mean pressure coefficients on the base of the SUV model vary from −0.23 to −0.1. The spectrum of the pressure coefficient fluctuation at the base of the model has a weak peak at a Strouhal number of 0.07. PIV measurements show a complex three-dimensional recirculation region behind the model of length approximately 1.2 times the width of the model.
Technical Paper

CFD Simulations for Flow Over Pickup Trucks

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.
Technical Paper

A Transient Water Analog of a Dual-Intake-Valve Engine for Intake Flow Visualization and Full-Field Velocity Measurements

It has been recognized that the fluid motion during the engine induction process has a significant effect on combustion in terms of efficiency and emissions. To understand the intake process, a transient water analog visualization engine has been developed. This model, which simulates a single cylinder engine, has a transparent dual-intake-valve cylinder head and a transparent cylinder and is used to study the in-cylinder and port flows both qualitatively and quantitatively during the induction process. A special illumination coding procedure and recording technique along with an image analysis method were also developed to obtain full-field cycle-resolved velocity information from the visualization images. Results obtained for this engine indicated that the flow field during the induction stroke is totally dominated by the generation of two jet flows which produce several vertical motions on different planes along the engine cylinder.
Technical Paper

A CFD Study of Drag Reduction Devices for a Full Size Production Pickup Truck

Various drag reduction strategies have been applied to a full size production pickup truck to evaluate their effectiveness by using Computational Fluid Dynamics (CFD). The drag reduction devices evaluated in this study were placed at the rear end of the truck bed and the tailgate. Three types of devices were evaluated: (1) boat tail-like extended plates attached to the tailgate; (2) mid-plate attached to the mid-section of the tailgate and; (3) flat plates partially covering the truck bed. The effect of drag reduction by various combinations of these three devices are presented in this paper. Twenty-four configurations were evaluated in the study with the best achievable drag reduction of around 21 counts (ΔCd = 0.021). A detailed breakdown of the pressure differentials at the base of the truck is provided in order to understand the flow mechanism for the drag reductions.