内燃机排气流动结构与能量耗散机制的高精度大涡模拟研究

In the context of energy saving and emission reduction, detailed study on the exhaust flow of Internal Combustion Engine (ICE) is very important to improve the thermal efficiency and reduce the emission of ICE. The loss of effective work (total pressure) in the exhaust flow of ICE reduces the residual energy utilization rate of the turbocharger. The flow structure affects the efficiency of the turbocharger and the exhaust gas recirculation (EGR) system. .However,the assembly related to ICE exhaust is too complex to be detailed test in lab. The traditional RANS method can not accurately simulate the separation flow in the exhaust port. Due to these reasons, it is still unclear of the flow structure and energy dissipation mechanism in the exhaust flow of ICE. It needs to be studied deeply..In this research, we will develop a high-fidelity large eddy simulation method (which includes new filters and new subgrid-scale stress models based on high order flux reconstruction algorithm) and apply this method to study the exhaust flow of ICE. The main focus is the flow structure and the energy dissipation mechanism in the exhaust flow of ICE. The emphasis is the relation between the separation flow and energy dissipation. This research will lay a theoretical foundation for reducing the effective work loss in the exhaust flow of ICE. This will improve the residual energy utilization of the turbocharger and make the energy saving and emission reduction.

在节能减排大背景下，精细化研究内燃机排气流动对于提高内燃机热效率、减少内燃机排放具有重要意义。内燃机排气流动的有用功（总压）损失降低了涡轮增压器的余能利用率，流动结构影响着涡轮增压器和废气再循环系统的效率。.由于内燃机排气部件复杂且伴随高速运动，精细化实验研究非常困难。内燃机排气过程存在大分离流动，传统数值模拟方法（雷诺平均模拟）精度不够。内燃机排气流动机理暂不清楚，能量耗散机制尚不明确,需要深入研究。.本项目结合通量重构高阶算法与大涡模拟方法，通过改进大涡模拟过滤器和亚格子模型，发展一种新的可用于内燃机排气流动精细化研究的高精度大涡模拟方法。应用该方法对真实内燃机模型的排气流动进行精细化数值模拟研究，弄清内燃机排气流动的复杂机理与能量耗散机制，重点考察大分离流动对总压损失的影响，为减少内燃机排气流动的有用功损失打下理论研究基础，提高余能回收系统的废气余能利用率，最终达到节能减排的目的。

在节能减排大背景下，精细化研究内燃机排气流动对于提高内燃机热效率、减少内燃机排放具有重要意义。内燃机排气流动的有用功（总压）损失降低了涡轮增压器的余能利用率，流动结构影响着涡轮增压器和废气再循环系统的效率。由于内燃机排气部件复杂且伴随高速运动，精细化实验研究非常困难。内燃机排气过程存在大分离流动，传统雷诺平均模拟精度不够。本项目按照基金任务书的计划执行，通过发展高精度大涡模拟的方法，对内燃机排气流动进行了精细化研究。.主要研究内容和结果包括：（1）测试和改进大涡模拟过滤器和亚格子模型，发展了一套高精度大涡模拟方法，并将该方法应用于平板湍流边界层和直管、弯管组合的内燃机排气管的大涡模拟研究。经过与实验数据对比，验证了该方法的可行性与精确性。（2）对内燃机排气管内的总压损失进行分段计量，发现内燃机排气流动的总压损失主要发生在靠近阀门的截面1到截面3区域。（3）通过本征正交分解方法，对恒定质量入流和周期动质量入流的流动结构进行分解，找出了影响SCANIA D12内燃机排气管流动能量耗散的主要流动结构:一是从阀门和气缸壁喷涌而出的高速射流在进入排气管后会形成绕阀门杆的回流；二是两个排气管交汇形成的汇流。从而弄清了内燃机排气流动的能量耗散机制，实现了研究目标。