• Wind and Structures
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• 제17권5호
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• pp.515-535
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• 2013

The present study aims to investigate characteristics of the flow structures around the Ahmed body by using both experimental and numerical methods. Therefore, 1/4 scale Ahmed body having $25^{\circ}$ slant angle was employed. The Reynolds number based on the body height, H and the free stream velocity, U was $Re_H=1.48{\times}10^4$. Investigations were conducted in two parts. In the first part of the study, Large Eddy Simulation (LES) method was used to resolve the flow structures around the Ahmed body, numerically. In the second part of the study the particle image velocimetry (PIV) technique was used to measure instantaneous velocity fields around the Ahmed body. Time-averaged and instantaneous velocity vectors maps, streamline topology and vorticity contours of the flow fields were presented and discussed in details. Comparison of the mean and turbulent quantities of the LES results and the PIV results with the results of Lienhart et al. (2000) at different locations over the slanted surface and in the wake region of the Ahmed body were also given. Flow features such as critical points and recirculation zones in the wake region downstream of the Ahmed body were well captured. The spectra of numerically and experimentally obtained stream-wise and vertical velocity fluctuations were presented and they show good consistency with the numerical result of Minguez et al. (2008).

• 한국전산유체공학회지
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• 제3권2호
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• pp.39-51
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• 1998

This paper describes the analysis of flow field around an automobile. The governing equations of the 3-D unsteady incompressible Navier-Stokes equations are solved by the iterative time marching scheme. The Chimera grid technique has been applied to efficiently simulate the flow around the side-view mirror. To validate the capability of simulating the flow around a ground vehicle, the flows around the Ahmed body with 12.5$^{\circ}$ and 30$^{\circ}$ of slant angles are simulated and good agreements with experiment and other numerical results are achieved. To validate Chimera grid technique, the flow field around a cylinder was also calculated. The computed results are also well agreed with other numerical results and experiment. After code validations, the flow phenomena around the ground vehicle are evidently shown. The flow around the side-view mirror is also well simulated using the Chimera grid technique.

• 한국전산유체공학회지
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• 제2권1호
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• pp.46-53
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• 1997

The flow field around a three dimensional minivan-like body has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations on a non-orthogonal curvilinear coordinate system using second-order accurate schemes for the time derivatives, and third/second-order scheme for the spatial derivatives. The Marker-and-Cell concept is applied to efficiently solve continuity equation. A H-H type of multi-block grid system is generated around a three dimensional minivan-like body. Turbulent flows have been modeled by the Baldwin-Lomax turbulent model. To validate present procedure, the flows around the Ahmed body with 12.5° of slant angle are simulated. A good agreement with other numerical results is achived. After code validation, the flows around a mimivan-like body are simulated. The simulation shows three dimensional vortex-pair just behind body. The flow separation is also observed on the rear of the body. It has concluded that the results of present study properly agreed with physical flow phenomena.

• 대한기계학회논문집B
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• 제20권11호
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• pp.3589-3597
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• 1996

The Reynolds-averaged Navier-Stokes equations with the equations of the k-.epsilon. turbulence model are solved numerically in a general curvilinear system for a three-dimensional turbulent flow around an Ahmed body. The simulation is especially aimed at the evaluation of three finite differencing schemes for the convection term, which include the upwind differencing scheme(UDS), the second order upwind differencing scheme(SOU scheme) and the QUICK scheme. The drag coefficient, the velocity and pressure fields are found to be changed considerably with the adopted finite differencing schemes. It is clearly demonstrated that the large difference between computation and experiment in the drag coefficient is due to relatively high predicted values of pressure drag from both front part and vertical rear end base. The results also show that the simulation with the QUICK or SOU scheme predicts fairly well the flow field and gives more accurate drag coefficient than other finite differencing scheme.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.565-568
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• 2002

In the flow analysis around a bluffbody such as road vehicles, drag reduction has been of the primary concern mainly due to the effect on fuel economy. To reduce the drag, which is mostly due to the pressure difference caused by the flow separation, the location of the separation and eddy sizes are controlled. However, less attention has been given to the effect of the lift. The effect of lift may cause the driving stability problem of the vehicle at high speed white heavy downward effect of lift together with the vehicle weight may require more power to drive the vehicle forward. It is considered worthwhile to pursue the optimal design of the low drag tail shape of the MIRA model while taking the lift effect into account, even though it is considered as a reference. To this end, a commercial multi-objective optimization code, FRONTIER, Is used together with the CFD code, STAR-CD. It is hoped that the results will provide more insight into the flow field around the bluffbody as transportation means.

• 한국자동차공학회논문집
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• 제21권3호
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• pp.30-42
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• 2013

This study investigates the effects of OSRVM mounting location and its configurations such as stalk height and housing height on the aerodynamic performance of the passenger car. In order to validate the flow solver, FLUENT which is very well known commercial code, the flow field around an Ahmed Body was analyzed numerically and compared with the experimental data. The predicted aerodynamic performance and flow patterns around a car show good agreements with the experimental data. Mounting location and stalk height should be designed while OSRVM is mounted on the car to evaluate the aerodynamic performance precisely. Housing height, however, may be designed independent of the car because the aerodynamic interference between housing height and car configuration is negligible.