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192 Laurent Dumas 7.1 Introducing Automotive Aerodynamics 7.1.1 A Major Concern for Car Manufacturers In the past, the external shape of cars has evolved particularly for safety reasons, comfort improvement and also aesthetic considerations. Consequences of these guidelines on car aerodynamics were not of major concern for many years. However, this situation changed in the 70’s with the emergence of the oil crisis. To promote energy conservation, studies were carried out and it was discovered that the amount of the aerodynamic drag in the fuel consumption ranges between 30% during an urban cycle and 75% at a 120 km/h cruise speed. Since then, decreasing the drag force acting on road vehicles and thus their fuel consumption, became a major concern for car manufacturers. Growing ecological concerns within the last decade further make this a critically relevant issue in the automotive research centers. The process of drag creation and the way to control it was first discovered experimentally. In particular, it was found that the major amount of drag was due to the emergence of flow separation at the rear surface of cars. Unfortunately, unlike in aeronautics where it can be largely excluded from the body surface, this aerodynamic phenomenon is an inherent problem for ground vehicles and can not be avoided. Moreover, the associated three-dimensional flow in the wake behind a car exhibits a complex 3D behavior and is very difficult to control because of its unsteadiness and its sensitivity to the car geometry. The pioneering experiments of Morel and Ahmed done in the late 70’s on simplified geometries also called bluff bodies, are now described in Sects. 7.1.2 to 7.1.4. 7.1.2 Experiments on Bluff Bodies Two major experiments have been done on bluff bodies, the first one by Morel in 1978 [18] and the second by Ahmed in 1984 [1]. The objective was to study the flow behavior around cars with a particular type of rear shape called hatchback or fastback. These experiments are even now used as a reference in many numerical studies [8, 10, 12, 13, 16]. The bluff body used by Ahmed, similar to the one used by Morel, is illustrated in Fig. 7.1. It has the same proportions as a realistic car but with sharp edges. More precisely, the ratio of length/width/height is equal to 3.33/1.5/1. In both cases, the rear base is interchangeable by modifying the slant angle denoted here as α. The Reynolds numbers are taken equal to 1.4 × 10 6 and 4.29 × 10 6 in the Morel and Ahmed experiments, respectively.
7 CFD-based Optimization for Automotive Aerodynamics 193 1044 470 Fig. 7.1 The Ahmed bluff body 7.1.3 Wake Flow Behind a Bluff Body α The most difficult flow region to predict is located at the wake of the car where recirculation and separation occur. It is also the region which is responsible for most of the car drag (see Sect. 7.1.4). In a time-averaged sense, two distinct regimes depending on the slant angle α, called Regime I and II, have been observed in the experiments done by Morel and Ahmed. The value of the critical angle αc between both regimes is approximately equal to 30 degrees in each experiment but can slightly change depending on the Reynolds number and the exact geometry. • Regime I (αc
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Optimization and Computational Flui
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Editors: Prof. Dr.-Ing. Dominique T
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vi Preface Our first research proje
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viii Contents 2.4.1 GoverningEquati
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x Contents 6.2.3 Parameterization..
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xii Contents 9.4.1 Multi-objectiveO
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xiv List of Contributors Gábor JAN
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Part I Generalities and methods
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4 Dominique Thévenin 12 10 8 6 4 2
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6 Dominique Thévenin Objective 10
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8 Dominique Thévenin Objective 10
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10 Dominique Thévenin Parameter 2
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12 Dominique Thévenin three-dimens
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14 Dominique Thévenin Let us come
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16 Dominique Thévenin References 1
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18 Gábor Janiga 2.1 Introduction D
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20 Gábor Janiga y Tinlet = 293 K 0
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22 Gábor Janiga y [mm] 25 20 15 10
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24 Gábor Janiga Table 2.1 Number o
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26 Gábor Janiga A dominates the in
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28 Gábor Janiga be shown later, th
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30 Gábor Janiga INPUT FILE Gambit
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34 Gábor Janiga ∆T ∆P Position
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36 Gábor Janiga ∆P [mPa] 2.2 2.0
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38 Gábor Janiga Table 2.3 Speed-up
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40 Gábor Janiga For all computatio
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42 Gábor Janiga y [mm] 4 2 0 -1 0
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44 Gábor Janiga Air mass flow-rate
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46 Gábor Janiga Temperature variat
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50 Gábor Janiga The modified k-ω
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52 Gábor Janiga Error for Re∗ =
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54 Gábor Janiga Error for Re∗ 20
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56 Gábor Janiga References 1. Ali,
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58 Gábor Janiga 43. Janiga, G., Th
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Chapter 3 Mathematical Aspects of C
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3 Mathematical Aspects of CFD-based
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Chapter 4 Adjoint Methods for Shape
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4 Adjoint Methods for Shape Optimiz
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Part II Specific Applications of CF
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112 Nicolas R. Gauger Nomenclature
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114 Nicolas R. Gauger Fig. 5.1 Cost
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116 Nicolas R. Gauger and the four
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118 Nicolas R. Gauger CL := 1 � C
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120 Nicolas R. Gauger the cost func
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122 Nicolas R. Gauger Table 5.1 An
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124 Nicolas R. Gauger The main adva
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126 Nicolas R. Gauger Spalart-Allma
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128 Nicolas R. Gauger (a) (b) Fig.
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134 Nicolas R. Gauger Fig. 5.10 Plo
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136 Nicolas R. Gauger drag, lift, s
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138 Nicolas R. Gauger solution of t
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140 Nicolas R. Gauger the presence
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8 Multi-objective Optimization in C
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Chapter 9 CFD-based Optimization fo
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9 CFD-based optimization for paperm
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292 Index heat exchanger, 222, 224,
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