大型运输机动力增升喷流效应数值模拟

参照C-17运输机发动机安装位置，考虑内、外涵道分开排气，建立了外吹式襟翼动力增升全机几何分析模型以及相应的巡航构型.采用结构化多块网格技术，基于雷诺平均Navier-Stokes方法，分别对全机增升构型和单独发动机动力喷流进行数值模拟验证，在此基础上对外吹式襟翼动力喷流效应展开研究.对于低速动力增升构型，发动机喷流大部分直接冲刷襟翼下表面而后向下偏转，部分高速气流经襟翼缝道引射并加速后吹向襟翼上表面，两部分气流在襟翼后缘汇合并向下游延伸，喷流冲刷襟翼时存在明显展向横流特征.在动力喷流影响下，不仅襟翼环量大幅增加，缝翼和主翼上的环量也均有所增加，全机可用升力系数和最大升力系数均突破了机械式增升装置的极限，达到4.0以上.同时，全机低头力矩大幅增加，为纵向配平带来额外的压力.对于相应的高速巡航构型，发动机喷流主要影响机翼下表面的压力分布，使得全机升力减小，阻力明显增大.动力增升构型在基本翼设计过程中应充分考虑喷流的影响. 

Numerical simulation of powered high-lift jet effects for large transport

Taking C-17 transport engine installation as reference and considering external mixing of engine jet gas streams, a powered high-lift configuration with externally blowing flap (EBF) and the corresponding cruise model were constructed. Based on the structured multi-block grid techniques and Reynolds-averaged Navier-Stokes methods, numerical validations were carried out on a high-lift model and a fan-jet engine nacelle, and then the EBF effects were investigated. For powered high-lift configuration at low speed, most jet flow impinged directly on the lower flap surfaces and then deflected downward, while the rest was sucked and speeded up by the slots, and then blown upon the upper flap surfaces. The two parts of them converged at the flap trailing edge and extended downward. Spanwise lateral flow characteristics existed when the jet flow affected on the flap. Circulations increased significantly not just around the flaps but also on the slat and main wing. Both the available and maximum lift coefficients were larger than 4.0, breaking through the limit of the traditional mechanical high-lift systems. Longitude trim problems may be severer due to larger nose down pitching moment. For the cruise model at high speed, the engine jet flow will obviously affect the pressure distributions on lower wing surface, making the lift decrease and the drag increase significantly. Thus jet effects should be well considered during the clean wing design for powered high-lift configuration.