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针对湍流角区三维分离流动中表面油流图画(油流显示)出现的差异和不同性质,综合采用表面油流流动显示、空间PIV实验以及数值模拟探究不同表面流动结构的性质、产生差异的原因及其与空间流动结构的关系。研究表明,较强分离情况下表面油流呈现的两条油流线均为三维分离线,即一次分离线(上游)与二次分离线(下游)。油流线是空间非定常流动的时均结果,空间非定常流动以四涡结构为主。一次分离线(上游)符合Lighthill的收拢渐进线三维分离模式,二次分离线(下游)则符合Maskell的包络线三维分离模式。由于较强的第一主涡和二次涡在近壁面产生强剪切,二次分离线体现出与一次分离线不同的狭窄而清晰的油迹堆积以及低剪切应力特征,因此二次分离线又可称为低剪切应力线。在低剪切应力线两侧是由第一主涡和二次涡引起的较高剪切应力区。
In view of the difference and different nature of the surface oil flow drawing (oil flow display) in the three-dimensional separation flow in the turbulent angular zone, the reasons of the differences are analyzed by the flow display of surface oil flow, the space PIV experiment and the numerical simulation to explore the properties of different surface flow structures And its relationship with the structure of spatial mobility. The results show that the two oil flow lines of the surface oil flow in the case of strong separation are three-dimensional separation lines, that is, the first separation line (upstream) and the second separation line (downstream). The oil flow line is the time-averaged result of the unsteady flow in space, and the unsteady flow in the space is dominated by the four-vortex structure. The first separation line (upstream) corresponds to Lighthill’s convergent asymptotic three-dimensional separation mode and the second separation line (downstream) corresponds to Maskell’s envelope three-dimensional separation mode. Due to the stronger first and second eddy generated strong shear in the near wall, the secondary separation line shows a clear and distinct oil accumulation and low shear stress characteristics different from the primary separation line. Therefore, the secondary Off-line can be called low shear stress line. On both sides of the low shear stress line is the region of higher shear stress induced by the first and second eddy vortices.