宽速域RANS-LES混合方法的发展及应用

摘要

The growing demands of aerospace industry require accurate prediction of unsteady flow details.Current Reynolds averaged Navier-Stokes (RANS) methods are unable to provide dynamic loads for unsteady turbulent flows at high Reynolds numbers, such as massively separated flows past complex geometries.Large eddy simulation (LES) and direct numerical simulation (DNS) are still too expensive for engineering applications.Hybrid RANS-LES methods, combining near-wall RANS regions and outer LES regions, are the most promising techniques for unsteady turbulent flows in engineering.First of all, a general introduction to several categories of hybrid RANS-LES methods was given to discuss their basic ideas and characteristics.Then, the development history of detached-eddy simulation (DES) type methods was presented together with the influences of high-accuracy time-marching methods, spatial discretization schemes and proper numerical dissipation.For both mechanism studies and engineering applications, multiple cases at Mach numbers varying from 0.1 to 20 show that hybrid RANS-LES methods are an ideal choice for the prediction of turbulent flow in engineering.Hybrid RANS-LES methods are capable of predicting complex features involved in massive separation.Future improvement includes the promotion in computation efficiency and embedded RANS/LES strategy for detailed flow past small local component.Big potential also exists for hybrid RANS-LES methods in areas closely related to unsteady flow, such as dynamic stall, combustion and aero-elastics/acoustics/optics.%传统的雷诺平均方法(RANS)已经不能满足大范围分离、激波振荡、压力脉动、动载荷等极端工况下的流动预测需求;大涡模拟(LES)、直接数值模拟(DNS)等方法资源耗费多、效率低,离工程湍流问题仍较为遥远.RANS-LES混合方法结合了RANS高效率和LES高精度的特点,近期有望大规模应用到工程湍流问题中.首先对现有的RANS-LES混合方法进行了归类,对各自的构造思想、特点进行了分析.然后报告了脱体涡模拟(DES)类方法的发展历程和现状,讨论了使用DES类方法计算分离流动时,对流项离散格式对分离特性、小尺度结构及频谱特性等的影响,并构造了自适应耗散函数.最后介绍了近年来国内外RANS-LES混合方法在宽马赫数范围(马赫数从0.1到20)内的机理研究和工程应用.现有的以DES类方法为代表的RANS-LES混合方法能够较为精细地模拟非定常大分离流动中的复杂现象,但在计算效率等方面还有较大的改进空间;植入式DES方法在模拟全机带部件流动上具有较高的效率和模拟精度,是重要的发展方向.RANS-LES混合方法在动态失速、燃烧、气动弹性、气动噪声、气动光学等与非定常流动密切相关的方面也有广阔的应用前景.