• Title/Summary/Keyword: Ahmed Body

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Experimental and numerical studies of the flow around the Ahmed body

  • Tunay, Tural;Sahin, Besir;Akilli, Huseyin
    • Wind and Structures
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    • v.17 no.5
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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).

Ahmed body의 Slant angle 변화에 따른 항력계수 분석

  • Gang, Gwon-Yong;Ryu, Sin-Gyu
    • Proceeding of EDISON Challenge
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    • 2015.03a
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    • pp.559-562
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    • 2015
  • 본 연구에서는 EDISON_CFD를 활용하여 승용차 모델을 단순화한 Ahmed Body의 후미 경사각 Slant angle $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$의 항력계수변화를 확인하였다. 결과 분석을 통해 Ahmed Body 후면의 후류와 항력계수의 변화 경향성이 같다는 것을 확인하였다. 항력계수는 자동차의 연비 및 최고속도 등 동력성능에 큰 영향을 미치므로 최저 항력계수를 찾아보았다. 각각의 경우에 EDISON_simulation 결과 값을 비교해보면 $15^{\circ}{\sim}30^{\circ}$ 사이에서 최저 항력계수를 갖는 것을 확인할 수 있었다. 정확한 값을 찾기 위해 Polynomial Curve Fitting을 사용하여 Slant angle 이 $22.91^{\circ}$일 때 최저항력계수 0.1375를 갖는 것을 확인하였다.

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Simulation of Three-Dimensional Turbulent Flows around an Ahmed Body-Evaluation of Turbulence Models- (Ahmed Body 주위의 3차원 난류유동 해석 - 난류모델의 평가)

  • Myong, H.K.;Jin, E.;Park, H.K.
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.7
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    • pp.873-881
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    • 1997
  • A numerical simulation has been carried out for three-dimensional turbulent flows around an Ahmed body. The Reynolds-averaged Navier-Stokes equation is solved with the SIMPLE method in general curvilinear coordinates system. Several k-.epsilon. turbulence models with two convective difference schemes are evaluated for the performance such as drag coefficient, velocity and pressure fields. The drag coefficient, the velocity and pressure fields are found to be changed considerably with the adopted k-.epsilon. turbulence models as well as the finite difference schemes. The results of simulation prove that the RNG k-.epsilon. model with the QUICK scheme predicts fairly well the tendency of velocity and pressure fields and gives more reliable drag coefficient. It is also demonstrated that the large difference between simulations and experiment in the drag coefficient is due to relatively high predicted values of pressure drag from vertical rear end base.

Simulation of Three-Dimensional Turbulent Flows around an Ahmed Body-Evaluation of Finite Differencing Schemes- (Ahmed body 주위의 3차원 난류유동 해석-유한차분도식의 평가-)

  • Myeong, Hyeon-Guk;Park, Hui-Gyeong;Jin, Eun-Ju
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.11
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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.

Analysis of the flow field around an automobile with Chimera grid technique (Chimera 격자기법을 이용한 자동차 주위의 유동장 해석)

  • An, Min-Gi;Park, Won-Gyu
    • Journal of computational fluids engineering
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    • v.3 no.2
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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.

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Aerodynamic Investigation on Platooning Formation For Improvement of Fuel Efficiency (연료 효율 개선을 위한 군집주행 배열 형태 분석)

  • Lee, Seung-Ho;Baek, Jong-Jin;O, Se-Jong
    • Proceeding of EDISON Challenge
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    • 2014.03a
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    • pp.591-596
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    • 2014
  • 본 논문에서는 EDISON_전산열유체 시스템을 활용하여 군집주행 형태 변화에 따른 항력계수 및 연료효율 변화를 분석하였다. 해석 대상은 자동차 형상을 단순화한 모델인 아흐메드 형상(Ahmed body)을 이용하였다. 동종차량 간 거리변화에 따른 항력계수 및 연료효율의 변화, 이종차량의 배열순서변화에 따른 항력계수 및 연료효율을 분석하며 연구를 수행하였다. 연구 결과, 4대의 동종차량 군집주행시 항력계수를 최대 69% 감소할 수 있으며 이에 따라 km 당 0.073L의 연료를 절감할 수 있다.

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An Experimental Study on the Aerodynamic Drag of Model Cars with Cooling Air Passage (냉각유동이 자동차항력에 미치는 영향에 관한 실험적 연구)

  • 안이기;정형호;김광호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.2
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    • pp.405-413
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    • 1994
  • This paper presents the experimental results of aerodynamic drags of model cars. The effects of cooling air on total drag were introduced by using momentum theorem. Vehicle-liked Ahmed body and 1/5 model car were used to evaluate the increments of drags due to the internal flow. The results were compared with momentum theorem and other's experiments and showed good agreements. In the case of Ahmed body, drags were increased by 22% due to the internal flow and decreased linealy by reducing internal air flow rates and inlet areas. The experiments on 1/5 model car with ill-defined air flow passage showed 10% increment of drag. The results of present study showed that cooling drag could be predicted by momentum theorem within small errors.

Incompressible Viscous Flow Analysis Around a Three Dimensional Minivan-Like Body (3차원 미니밴 형상 주위의 비압축성 점성 유동 해석)

  • Jung Y. R.;Park W. G.;Park Y. J.;Kim J. S.;Hong S. H.
    • Journal of computational fluids engineering
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    • v.2 no.1
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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.

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Optimal Design for the Low Drag Tail Shape of the MIRA Model (MIRA Model 후미의 저저항 최적 설계)

  • Hur Nahmkeon;Kim Wook
    • Journal of computational fluids engineering
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    • v.4 no.1
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    • pp.34-40
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    • 1999
  • Drag reduction on vehicles are the main concern for the body shape designers in order to lower the fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can be minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain an optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having the lowest drag coefficient which is about 6% lower than that of the original shape has been successfully obtained within number of iterations of tile optimal design loop.

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Multi-objective Optimal Design for the Low Drag Tail Shape of the MIRA model with the Lift Effect taken into account (양력 효과를 고려한 MIRA model 후미의 저저항 다목적 최적설계)

  • Lee Juhee;Lee Kyunghuhn;Kim Joonbae
    • Proceedings of the KSME Conference
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    • 2002.08a
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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.

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