等热流边界条件下湍流边界层热条纹间距的数值研究

I. Tiselj, E. Pogrebnyak, A. Mosyak, G. Hetsroni
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引用次数: 2

摘要

对水槽内完全展开的热场进行了直接数值模拟。在加热底部施加恒热流密度边界条件,可以对壁面温度波动进行追踪。在自由表面上应用了动量的自由表面边界条件和温度的绝热边界条件。在此边界条件下,能量方程的病态性通过附加约束消除:将平均无因次壁面温度固定为零。恒摩擦雷诺数Re=171,普朗特数1和5.4进行DNS。边界条件的类型对平均温度的分布没有影响。两种边界条件的主要区别在于温度均方根波动,在恒定热流边界条件下,温度均方根波动在壁面上保持非零值,而在恒定无因次温度条件下,温度均方根波动在壁面上保持零值。在近壁区域的偏度、平整度和其他湍流统计数据的行为中也可以看到某些变化。一个重要的问题是等通量壁面上的热条纹间距和壁面附近的速度条纹间距之间的差异。在等温壁面边界条件下,热条纹与速度条纹密切相关,而等流壁面附近的温度条纹与速度低速条纹不重合。DNS表明,壁面附近的热条纹间距与普朗特数有关。热条纹间距大于速度条纹间距,并在普朗特数Pr=5.4时接近已知的速度条纹间距值(90-100壁单位)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Numerical study of thermal streak spacing in turbulent boundary layer with constant heat-flux boundary condition
Direct numerical simulation (DNS) of the fully developed thermal field in a flume was performed. Constant heat flux boundary condition was imposed on the heated bottom in a way, which allowed tracing of the temperature fluctuations on the wall. Free surface boundary conditions for momentum and adiabatic boundary condition for temperature were applied on the free surface. Ill-posedness of the energy equation with such boundary conditions was removed with an additional constrain: average non-dimensional wall temperature was fixed to zero. DNS was performed at constant friction Reynolds number Re=171 and Prandtl numbers 1 and 5.4. The type of the boundary condition did not affect the profile of the mean temperature. The main difference between two types of boundary conditions is in the temperature RMS fluctuations, which retain a nonzero value on the wall for constant heat flux boundary condition, and zero for constant non-dimensional temperature. Certain changes are visible also in the behavior of skewness, flatness, and other turbulent statistics in the near-wall region. An important issue is the difference between the thermal streak spacing on the isoflux wall and the velocity streak spacing near the wall. While the thermal streaks closely follow the velocity streaks for isotemperature wall boundary condition, the temperature streaks near the isoflux wall do not coincide with the velocity low speed streaks. The DNS shows that thermal streak spacing near the wall depends on Prandtl number. Thermal streak spacing is larger than the velocity streak spacing and is approaching to the well known value of the velocity streak spacing (90-100 wall units) at Prandtl number Pr=5.4.
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