二维涡融合特性分析

Analysis of 2D Vortices Merging Characteristics of an Aircraft

数值模拟二维涡融合现象,确定涡融合判据,分析涡融合基本过程,得到了融合过程的空间、时间特征。根据融合速率将融合过程分成4个阶段:①准稳态阶段;②涡量传输阶段;③涡量耗散阶段;④融合稳定阶段,给出各阶段的持续特征时间尺度,指出第3阶段发生了"反弹"现象,进一步分析不同雷诺数下的涡融合过程,得出不同雷诺数下涡融合过程具有"相似"特性的结论。

Trailing-edge vortices merging occurs when an aircraft takes off and lands.Two vortices of equivalent strength merge into one vortex at an approximate distance 5 to 10 times the wing span away.In the full paper,we discuss the 2D vortices merging criterion and derive its formula.Furthermore,we analyze the general characteristics in terms of time and space during the vortices merging process.We also conduct numerical simulation of vortices merging through the N-S equation.The simulation produces the distance between two vortex cores at different moments,which was reflected by the curve presented in Fig.5 in the full paper.The curve divides the vortices merging process into the following four stages：（1） quasi-stability sage,（2） convection stage,（3） diffusion stage,and （4） stable merging stage,and the duration of the four stages shown in Table 1 reveals the length of time needed for vortices to diffuse in air.The curve also indicates that at the third stage the ＂rebound＂ phenomenon occurs due to stronger diffusion effect.The ＂rebound＂ quantity is 0.05 b0.The simulation results,as shown in Fig.7 in the full paper,also inform us that the vortices merging processes have similarities under different Reynolds numbers.The ＂rebound＂ also occurs under different Reynolds numbers and has the same rebound quantity at Reynolds numbers 750,1 500,and 2 250.