基于瞬态模拟的厢式货车底部附加装置减阻机理研究

Aerodynamics drag reduction is one of the key issues of saving energy for van. The external flow around truck body has the characteristics such as fully three-dimensional, unsteady, large separation zone and complex vortex structures etc.Investigation of the structures of such flow is the key to digital design of low aerodynamics drag body. This project studies the drag reducing mechanism of van underbody based on unsteady large eddy simulation (LES). First based on energy transfer theory, the Truncated Navier-Stokes (TNS) model is modified and improved to suitable for external flow around truck body through analysis of energy spectrum, characteristics length scales and vortex ructures etc. Then the TNS model is applied to transient flow of Ahmed model and a real truck model. The evolution mechanism of flow vortex sturctures is studied. And The model is verified by experiment data. At last, the underhood flow of van with small drag reduction appendix is studied by LES. The influence of the structure parameters of truck body and appendix on flowfield and aerodynamic drag is analyzed. And the detail small flow structures around drag reduction device is discussed and is optimized. This project combines LES with unsteady flow around van. The details of flow around the small scale drag appendix is studied using the advantage of LES. It will help to understand the aerodynamic characteristics of truck in-depth. It provides the basis for the new design of truck body shape and underhood drag reduction device, which has important theoretical significance and engineering application value.

降低气动阻力是厢式货车节能的关键问题之一。货车外流场具有三维效应强、非定常、分离区多和涡结构复杂的特点，对其流动结构进行详细研究是高效低阻车身数字化设计的关键。本项目在基于瞬态大涡模拟的基础上对货车车身底部减阻机理进行研究。首先基于湍流能量传递理论，通过分析湍流能谱、特征尺度、涡结构等，发展和完善适合车身外流场的大涡TNS模型；然后将TNS模型应用于Ahmed车模和一款真实货车车身瞬态流场流场研究，揭示车身非定常流场结构演变机理，并结合实验数据进行完善；最后对加装了小尺度的货车底部新型附加装置流场进行大涡模拟，分析车身、附加装置结构参数对流场及阻力的影响机理，探讨减阻装置局部流动细节并优化。本项目将TNS模型和车身瞬态流场结合起来，利用大涡模拟优势对小尺度减阻装置局部流场进行研究，将有助深入了解货车空气动力学特性，为车身造型及减阻设计提供依据，具有重要的理论研究意义和工程实际价值。

汽车节能减排得到越来越多的关注，货车能耗占了约一半的汽车石油消耗，降低货车气动阻力是未来货车发展趋势，符合国家绿色发展的重大需求。本项目采用非定常瞬态模拟技术对货车车身尾部和底部加装被动减阻装置的减阻机理进行了详细的研究。首先对不同湍流模型在货车减阻装置方面的应用进行了深入研究，对比了RANS，非定常RANS，DES，IDDES，LES等多种湍流模型，并根据货车尾涡流场进行了修正和改进；然后对Ahmed车模进行了瞬态模拟，研究了多种仿生减阻装置的减阻和降噪机理；发展了一种新型的增强湍流减阻方法；接着对车模原型和加装减阻装置的模型进行了系列风洞实验，验证了减阻结果和仿真模型；最后对底部减阻进行了系列研究，揭示了诱导减阻的机理和区别，最后结合数字化优化设计对减阻装置进行了优化。本项目通过数字仿真和优化方法，发展了适合小尺度减阻装置局部流场的仿真技术，对货车尾部、底部减阻进行了系列深入的研究，将有助深入了解货车局部小尺度空气动力学特性，为车身造型及减阻设数字化设计提供依据，具有一定的理论研究意义和较好的工程实际价值，其结果可推广到工业界。