三维跨音速边界层的稳定性分析及转捩预测研究

Drag reduction by laminar flow is one of the most promising technologies in aircraft design. Due to its significant impact to the reductions of aircraft fuel consumption, environmental pollution, and operating cost, this technology is a key direction in the aircraft technology development worldwide. Here, the primary difficulty is the accurate prediction of the laminar-turbulent transition on main aircraft components and the deep understanding of the complex instability mechanisms in three-dimensional (3D) transonic boundary layers. The linear stability theory (LST) has proven to be very fruitful in this area and has resulted eN method for simple cases. However, today's engineering practices need more reliable transition prediction methods that can handle more complex situations. . Targeting the transition prediction problems in civil aircraft aerodynamic design, this project intends to extend the traditional linear stability theory to 3D compressible cases and analyze the TS and cross-flow instabilities in the transonic boundary-layer on typical swept wings. The goal of this research is to construct a transition prediction method incorporating multi-instability mechanisms. The result will be compared with that of Reynolds-averaged Navie-Stokes (RANS) computations based on turbulence transition models and calibrated with existing experimental data. Furthermore, through the application of the method developed to the aerodynamic designs of laminar-flow wings and nacelles, we intend to develop a new CFD methodology which couples 3D LST and RANS computations.

层流减阻是民机设计中最具吸引力的减阻技术之一，它对于降低飞机油耗，减少环境污染，降低运营成本作用显著，是我国民机技术发展需要深入研究的重点方向。其技术难点在于准确预测飞机主要部件上的层流湍流转捩行为，重点是对三维跨音速边界层的复杂失稳机制的把握。基于线性稳定性理论的eN方法，只提供了适用简单情形的思路，而工程应用中亟需处理真实复杂情况的可靠转捩预测手段。. 本项目拟围绕民用飞机气动设计中的转捩预测问题，将传统的线性稳定性理论扩展到三维可压缩情形，重点针对机翼上跨音速边界层的TS波不稳定性和横流不稳定性展开分析；构建能合理反映多重流动失稳机理的转捩预测方法，同时与基于湍流/转捩模型的RANS方法进行数值比较，并利用已有试验数据进行校正；进一步结合层流机翼和层流短舱设计中的转捩预测应用，发展三维LST与RANS结合的气动计算方法。

项目背景：层流减阻是民机设计中最具吸引力的减阻技术之一，它对于降低飞机油耗，减少环境污染，降低运营成本作用显著，其技术难点在于准确预测飞机主要部件上的层流湍流转捩行为，而工程应用中亟需处理真实复杂情况的可靠转捩预测手段。.研究内容：围绕民用飞机气动设计中的转捩预测问题，将传统的线性稳定性理论扩展到三维可压缩情形；构建能合理反映多重流动失稳机理的转捩预测方法；进一步结合转捩预测应用，发展三维LST与RANS结合的气动计算方法。.主要结果：一是构建了基于LST 的三维跨音速边界层的稳定性分析方法，完成了三维和二维线性稳定性方程的理论推导，实现了二维不可压边界层和三维可压缩边界层稳定性分析计算方法；二是利用LST稳定性方程开展了三维跨音速边界层分析，分析了二维槽道Poiseuille流、二维平板边界层Blasius流、二维翼型可压缩边界层、三维机翼可压缩边界层的稳定性；三是研究了CF不稳定性引起转捩的三维eN预测方法，改进了基于eN的三维横流转捩预测方法，完成层流机翼转捩风洞试验及数据分析研究；四是初步搭建了三维LST 转捩预测与RANS 结合的气动计算方法，形成了基本流程，利用某自然层流短舱方案，结合风洞试验数据进行了对比预测研究。.科学意义：本项研究为基于三维LST的转捩预测方法融入工程气动设计的计算流程奠定了初步基础。.