摘 要

进气系统是发动机十分重要的组成部分，它的布置形式和结构参数对发动机的充气效率、进气阻力、进气均匀性、缸内混合气运动和燃烧过程有着重要的影响，从而影响发动机的动力性、经济性和排放特性。而发动机进气系统内气体流动非常复杂,瞬变性强,分布也不均匀而且其内流系统的运动对发动机充气性能的影响很大。但通过数值模拟方法可以获得流道内气体流动的具体情况,并且大大缩减实验周期,是现在研究进气过程气体流动的重要手段。本文通过仿真软件对发动机进气系统的流场情况进行了研究。

本文用CATIA建立了进气系统及进气歧管的三维模型。在HyperMesh中对三维模型进行了面的前处理工作，并划分了模型的面网格，在STAR-CCM 中对模型的面网格进行质量检查，对有质量问题的面网格进行修改，确保模型的面网格质量达到计算要求之后，划分模型的体网格，最后进行边界条件的设置,进行流场分析。根据流场分析结果，计算了进气歧管的质量流量和进气均匀性；对进气系统提出优化方案，并对优化方案进行仿真分析并与原方案进行对比。

通过对进气歧管的压力场、速度场进行了分析，可发现当不同的进气歧管出口开启时，进气管内的气体压力变化规律基本是相同的，在进气入口处压力较高，在出口处压力较低，并且压力从进气入口到进气出口呈现压力逐渐降低趋势，稳压腔内气体压力没有明显变化且压力分布较为均匀。并计算了进气歧管的质量流量和进气均匀性，通过计算发现该进气歧管的进气均匀性比较好，满足工业设计要求。通过对进气系统的速度场压力场及湍动能场的分析，可以看到进气入口处压力较大，产生的原因为入口处管道为弯管，速度方向发生改变，所以进口处压力较大；压力在引气管中没有明显变化，速度在引气管中也没有明显变化，发现滤清器下部有明显的涡流存在，并且涡流存在处湍动能较高，对进气性能影响较大。所以对进气系统的滤清器部分进行了优化。优化后的进气系统进气规律与优化前的大体相同，但优化后的滤清器涡流减弱，湍动能减小，压力损失降低，提高了进气效率。

本文通过对发动机进气系统的CFD数值模拟计算，分析了进气系统流场的分布情况并进行优化，对以后发动机进气系统的设计和改进具有重要的理论指导意义。

关键词：进气系统；CFD；流场分析；结构优化

Abstract

The air intake system is a very important part of the engine, its layout and structural parameters of the engine's inflation efficiency, intake resistance, intake uniformity, in-cylinder mixture movement and combustion process has an important impact, thus affecting the engine Power, economy and emission characteristics. The gas flow in the engine intake system is very complex, the transient is strong, the distribution is not uniform and the movement of the internal flow system has a great influence on the engine inflatable and performance. However, the numerical simulation method can obtain the specific situation of gas flow in the flow channel by calculation, and can greatly reduce the experimental period, which is an important method to study the gas flow in the intake process. In this paper, the flow field of the engine intake system is studied by simulation software.

In this paper, three-dimensional model of intake system and intake manifold is established by CATIA. In the HyperMesh, the three-dimensional model is pre-processed, and the surface mesh of the model is divided. The surface mesh of the model is checked in STAR-CCM , and the surface mesh with quality problem is modified to ensure that After the grid quality of the model reaches the calculation requirement, the body grid of the model is divided, and the boundary condition is set up and the flow field is analyzed. According to the results of flow field analysis, the mass flow and intake uniformity of the intake manifold are calculated. The optimization scheme is put forward for the intake system, and the optimization scheme is simulated and compared with the original scheme.

Through the analysis of the pressure field and velocity field of the intake manifold, it can be found that the gas pressure change in the intake pipe is basically the same when the inlet of the intake manifold is opened, and the pressure is higher at the inlet entrance , The pressure at the outlet is low, and the pressure from the inlet to the intake port shows a gradual downward trend in pressure, gas pressure within the regulator cavity did not change significantly and the pressure distribution is more uniform. And the mass flow and intake uniformity of the intake manifold are calculated. It is found that the intake manifold uniformity of the intake manifold is better and the industrial design requirements are met. Through the analysis of the velocity field and the turbulent energy field of the intake system, it can be seen that the pressure at the inlet of the inlet is large. The reason is that the pipe at the inlet is bent and the velocity direction is changed. Therefore, the pressure at the inlet ; The pressure did not change significantly in the airway, and the speed did not change obviously in the airway. It was found that there was obvious eddy current in the lower part of the filter, and there was a high turbulence energy in the eddy current, which had a great influence on the air intake performance. So the filter part of the intake system was optimized. The optimized law of the intake is the same as that before the optimization, but the eddy current of the optimized filter is weakened, the turbulence energy is reduced, the pressure loss is reduced, and the inlet efficiency is improved.

In this paper, the CFD numerical simulation of the engine intake system is analyzed and the distribution of the flow field of the intake system is analyzed and optimized. It is of great theoretical significance for the design and improvement of the engine intake system

Key words: intake system; CFD; flow field analysis; structural optimization

目录

摘要 I

Abstract II

第1章 绪论 1

1.1课题背景及研究意义 1

1.2国内外的研究现状 1

1.2.1国内研究现状 1

1.2.2国外研究现状 2

1.3本文研究主要内容 3

第2章 计算流体动力学的数学模型 4

2.1流体动力学的控制方程 4

2.1.1质量守恒方程 4

2.1.2能量守恒方程 5

2.1.3动量守恒方程 5

2.2 控制方程的离散方法 5

2.2.1有限差分法 6

2.2.2有限元法 6

2.2.3有限体积法 6

2.3流场的求解方法 6

2.4湍流模型简介及分类 7

2.5本章小结 7

第3章 发动机进气系统建模及流动特性仿真分析 8

3.1发动机进气系统物理模型分析 8

3.2网格划分 8

3.2.1进气系统的网格划分 8

3.2.2进气歧管的网格划分 9

3.3发动机进气系统边界条件的确定 10

3.3.1进气系统边界条件的设置 10

3.3.2进气歧管边界条件的设置 11

3.4发动机进气系统流场仿真结果分析 12

3.4.1进气系统流场仿真结果分析 13

3.4.2进气歧管流场仿真结果分析 15

3.5 本章小结 18

第4章 发动机进气系统优化设计与分析 19

4.1发动机进气系统的结构优化 19

4.2优化后发动机进气系统的流场分析与结果对比 20

4.3 本章小结 22

第5章 结论 23

5.1工作总结 23

5.2研究展望 23

参考文献 25

致谢 27

第1章 绪论

1.1课题背景及研究意义

自发动机被发明以来，就在人类社会的发展过程中起到了不可替代的作用。而作为发动机十分重要的组成部分进气系统，它的结构参数和布置形式对发动机的充气效率、进气均匀性、进气阻力等有着十分重要的影响，进而影响发动机的经济性、动力性和排放特性等。因此，进气系统的设计情况对发动机来说就十分重要了。发动机进气系统内气体流动情况十分复杂,且瞬变性强，但气体在进气系统内的运动情况对发动机性能有很大影响。所以必须了解发动机内气体流动的情况,才能根据流动情况设计出比较合理的进气系统结构。因此对发动机进气系统进行流动特性仿真分析及优化就显得十分重要。

1.2国内外的研究现状

1.2.1国内研究现状

国内的很多大学都有进气系统方面的研究，如武汉理工大学的王卫华用三维计算流体动力学软件对进气道模型进行了不同气门升程情况下稳态流动的三维数值模拟计算,获得其内部的压力场、速度场等的详细分布情况,计算出各升程下的气体流量系数和涡流比,分析了双进气道在截面上的气流干涉情况,为气道设计和改进提供重要的理论依据^[1]。太原理工大学的靳红玲分析了上置进气系统的流场特性，对不同气门升程的速度场、压力场、和湍动能场进行分析，为气道的进一步优化提供了必要保障^[2]。

湖南大学的李志丰研究了进气管中气流运动的波动效应和能量损失以及进气过程中一维非定常流动的数值解法，并用GT-Power软件建立发动机模型，分析进气管长度变化和稳压腔容积変化对发动机性能的影响^[3]。天津大学的石皓天利用三维流体计算软件 AVL_FIRE对GDI汽油机的进气歧管进行模拟仿真探讨不同喷油器安装位置及角度对管内油气混合状态的影响，确定最佳方案^[4]。