【摘要】 采用直接数值模拟方法,研究了稳定温度分层条件下均匀剪切湍流(homogeneous shear turbulence, HST)中的热量逆输运特性;采用聚类连通方法深入研究了热量逆梯度输运结构的统计特性,包括其几何特征和空间分布.流场雷诺数设定为Re_x=5 000,理查森数Ri分别取值为0、0.1、0.2.模拟结果揭示了稳定温度分层对湍流结构的显著影响:引入温度分层后,逆梯度输运区域显著增多,且相关结构在流向方向上的尺寸被拉长.此外,稳定分层还导致结构与流向之间的倾斜角度减小.在垂向方向上,“上抛”与“下扫”热通量呈现沿对角线的成对分布特征,且随着分层强度的增大,“下扫”结构更倾向于出现在“上抛”结构的下方.该研究加深了对分层剪切湍流中热量逆梯度输运的认识,也有益于探索逆梯度输运现象的物理机制.更多还原

【Abstract】 By using the direct numerical simulation method, the characteristics of countergradient heat transport in homogeneous shear turbulence under stable thermal stratification were investigated. The cluster connectivity method was employed to thoroughly examine the statistical properties of counter-gradient heat transport structures, including their geometric features and spatial distribution. The Reynolds number was set at Re_x=5 000, and the Richardson numbers Ri were set to 0, 0.1, and 0.2, respectively. The simulation results reveal significant impacts of stable thermal stratification on turbulence structures. The number of counter-gradient transport regions significantly increases by introducing thermal stratification, and the relevant structures are elongated in the streamwise direction.Furthermore, the inclination angle between the structures and the streamwise direction is reduced by stable stratification. In the vertical direction, “ejection” and “sweep” heat fluxes exhibit a characteristic of paired distribution along the diagonal direction, and with increasing stratification intensity, “sweep” structures tend to appear below “ejection” structures.The findings of this study deepen the understanding of counter-gradient heat transport in stratified shear turbulence and are useful for further exploration of the physical mechanisms underlying the counter-gradient transport phenomenon.更多还原