细长体大攻角绕流非对称性形成机理的尺度自适应模拟研究

The flow around slender body at high incidence usually shows remarkable asymmetry, which brings immense difficulty in the flight control of aerocraft with slender forebody and then weakens the flight maneuverability and agility of aerocraft. This aerodynamic puzzle is going to be studied in the current work with the rising Scale-Adaptive Simulation (SAS) method that gives considerations to both precision and efficiency of the computation. According to the Menter-SAS model, a fire-new SAS model is to be constructed by both modifying the formation of von Karman length scale and upgrading the basic turbulence model. The fresh SAS model can be employed to more advantageously predict the flow, especially the small-scale vortices and unsteady characteristics, around slender body at high incidence. Based on the computational results, the origin of the flow asymmetry is analyzed combined with the flow stability theory. The fresh SAS model not only gets over the reliance of interface between RANS and LES on grid, but also considers the Wall-Adaptive Local Eddy-viscosity (WALE) and the nonlinear effect of Reynolds stress, which provides a new option for the precise prediction of unsteady turbulent flow with massive separation. The achievements obtained here with numerical method are significant for cognizing the exact flow structure and aerodynamic characteristics around slender body at high incidence, comprehending the origin of the flow asymmetry, and developing the effective active methods for flow asymmetry control at high incidence.

细长体大攻角绕流表现出明显的非对称性，这给前体具备细长形状特征的飞行器的飞行控制带来了极大困难，显著降低了飞行器飞行的机动性和敏捷性。本项目拟运用新兴的兼顾计算精度与效率的尺度自适应模拟（Scale-Adaptive Simulation，SAS）方法来研究这一气动难题。在Menter-SAS模型基础上，通过修改von Karman长度尺度构造和升级基准湍流模型来构造一全新SAS模型，能较好预测细长体大攻角绕流，尤其是小尺度涡结构和非定常特性，并结合流动稳定性理论来探讨绕流非对称性形成机理。全新SAS模型除能克服RANS/LES分界面的网格依赖性外，还将计及物面自适应当地涡粘性和雷诺应力非线性效应，从而为非定常大尺度分离湍流的准确预测提供一个新选择。本项目数值研究成果对掌握细长体大攻角绕流确切的流场结构和气动力特性、理解非对称性形成机理、发展大攻角非对称主动控制措施具有重要意义。

为减小波阻，超音速飞机、导弹等常具有细长体外形，细长体大攻角绕流背涡轴向演化表现出明显的非对称性，显著降低了飞行器的飞行机动性与敏捷性，并给飞行控制带来了极大的困难。由于流动复杂性，细长体大攻角绕流非对称性形成机理至今仍颇具争议。本项目运用新兴的兼顾计算精度与效率的尺度自适应湍流模型来研究细长体大攻角非对称绕流这一气动难题，开展了如下工作。. (1) 基于SST-SAS湍流模型及LES类壁面涡粘性自适应（Wall-Adaptive Local Eddy-viscosity，WALE）模型，通过修改von Karman长度尺度Lvk和升级基准EARSM湍流模型构造了全新SAS模型，新型SAS模型除能克服RANS/LES分界面的网格依赖性外，还计及了耗散阻尼效应及雷诺应力的非线性效应，计算结果表明全新模型能较好地预测细长体大攻角绕流的流场结构及气动力特性，尤其是小尺度涡结构和细长体尾部的非定常特性。. (2) 在选择适合细长体大攻角绕流涡识别方法的基础上，系统分析了攻角大小、来流马赫数、头部微小扰动条件等主控参数对绕流非对称性形成过程的影响情况，结果表明：攻角大小、自由来流马赫数对细长旋成体有攻角绕流非对称性的影响主要是通过改变不稳定对称流型的轴向起始位置来实现的；头部扰动条件对绕流非对称性的影响则主要是通过改变扰动初始能级和扰动速度方向来实现的。. (3) 结合流动稳定性理论探讨了细长体大攻角绕流非对称性的形成过程。流场中存在不稳定单再附点流型且流场中存在一定能级的适当扰动是细长体大攻角绕流非对称性产生必须具备两个条件。. (4) 基于主动控制思想验证了应用微型射流涡流器对细长体大攻角绕流非对称性进行控制的有效性，它主要通过与绕流相互作用所形成的射流集中涡改变绕流头涡在头部尖顶附近的非对称程度来实现对绕流非对称性的主动控制。. 本项目提出的全新SAS模型为大尺度分离湍流的准确预测提供了新的选择，数值模拟结果对进一步认识细长体大攻角绕流的流场结构和气动力特性、理解和掌握非对称性形成机理、发展行之有效的大攻角主动控制措施具有重要意义。