CFD analysis in the development of the latest trai

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CFD analysis in body development

1 Preface

in recent years, following the successful application of structural finite element analysis (FEM) in the development of automotive products, CFD analysis is also increasingly applied to the process of body development. The development of the car body is closely related to the analysis of the air flow inside and outside the car. For example, the shape of the car body determines the shape of the external flow field of the car, thus determining the size of the wind resistance of the car. Whether the front air inlet is reasonable determines the heat dissipation effect of the engine. The design of automobile air-conditioning system affects whether the air volume distribution of each outlet is reasonable and the ability to regulate air quality. The flow condition of the engine room directly affects the effect of heat dissipation, and so on. CFD analysis can use the method of computer simulation to give a timely prediction of the above problems in the early stage of the design, and improve and optimize the design. If these problems cannot be found in time in the design stage, and the design can be changed after finalization and production, it will cause a huge waste of cost and cycle, and the loss of the market is irreparable

the principle of CFD analysis is computational fluid dynamics. Most CFD software uses the finite volume method to solve the N-S equations (nonlinear equations) of fluid mechanics, and gives out whether to choose ball screw or trapezoidal screw as the knot of concern in the flow field? Before making a decision. It can be carried out on high-end computers, and the efficiency will be significantly improved on multi CPU machines. CFD analysis does not need a solid sample vehicle, and more detailed results can be obtained than the test. FAW technology center has carried out a lot of CFD analysis on the external and internal flow of the body in the past five years, which provides a scientific basis for the design. This paper briefly introduces several main aspects

2. Aerodynamic characteristics analysis and optimization of the whole vehicle

2.1 aerodynamic characteristics analysis of passenger cars

with the increasingly fierce market competition, the shape design of passenger cars has received more and more attention, and the wind resistance (aerodynamic resistance coefficient) of modern cars is getting smaller and smaller

FAW technology center has successfully completed CFD analysis for many times in body development in recent years, and predicted the resistance coefficient, etc., with an error of about 5% compared with the wind tunnel test. The digital model used in the analysis can come from the measurement of the sludge model. If computer aided modeling (CAS) is used in the shape design, it can also be directly output by the modeling software and linked with CAS. If the existing digital model of finite element analysis of vehicle body is supplemented, it can also be used as the original data of CFD analysis. CFD software adopts fluent, and the hardware is a multi CPU high-performance computer. Figure 1 shows the flow field obtained from CFD analysis of M6 car

figure 1

2.2 analysis of aerodynamic characteristics of commercial vehicles

competition in the commercial vehicle market requires manufacturers to continuously reduce fuel consumption, improve their transportation capacity, and reduce their aerodynamic resistance coefficient is an important way. Commercial vehicles usually do not have a good streamline, so there is greater potential to improve their aerodynamic performance. By means of CFD analysis, FAW technology center has carried out a series of studies on the aerodynamic optimization of the cab shape of flat head vehicles, decomposed each part, and studied its contribution to drag reduction respectively (see Figure 2)

figure 2

for the product vehicle, the resistance coefficient can be greatly reduced by appropriately installing deflectors, deflectors and other measures. Figure 3 shows the results of CFD analysis of a product vehicle after installing a shroud. The calculation shows that the drag coefficient can be reduced by 15-20% after adding a deflector

figure 3

3 Air conditioning system flow analysis

in order to ensure the reasonable design of the air conditioning system, CFD analysis of the air conditioning system is an economic and effective means. The air flow direction of the air conditioning system is: fan → three box assembly → air duct → all air outlets. If the design of one part is unreasonable, it may lead to excessive air volume difference at each outlet, unreasonable cooling/heating air volume and other problems. CFD analysis of air conditioning system can be divided into two categories: Fan Characteristic Analysis and three box/duct flow analysis. The CFD analysis of the fan can give its characteristic curve, and the shell can be improved by pressing the test piece into a drum shape. The flow analysis of the three boxes/air ducts can give the proportional relationship of the air volume distribution of each outlet, so as to make adjustments to the design in time. Figure 4 and figure 5 respectively show the results of CFD analysis of air conditioning fan and three box/air duct by FAW technology center. Through the analysis, the original design has been improved and the design quality has been improved

4. Engine room flow analysis

the shape of the engine room directly affects the flow in the cabin. We can design different fixture dynamic conditions (related to the body) according to different samples and experimental methods. FAW analyzed the airflow in the cabin using CFD analysis, improved the flow in the cabin, and improved the heat dissipation efficiency of Jinfa's business in 3C, led, pipeline, highway facilities, building materials and other sectors (Figure omitted)

Figure 6 shows Opel's CFD analysis of optimizing the shape of engine room and inlet grille (the bottom right corner is the final result)

figure 6

5 Flow analysis of the passenger compartment

CFD analysis can be used to analyze the airflow and temperature comfort of the passenger compartment, and timely adjust the airflow at the outlet of the air conditioner to ensure the air quality of the passenger compartment and improve the comfort (Figure 7)

Figure 7 Figure 8

6 Aerodynamic noise analysis

besides vibration noise, aerodynamic noise is an important component of vehicle noise, including external airflow noise and internal fan noise. The frequency spectrum of aerodynamic noise can be given by CFD analysis. Through improving the design, the aerodynamic noise can be reduced and the vehicle quality can be improved (see Figure 8 fan and Figure 9 fan noise spectrum)

figure 9


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