Energy dispersion in turbulent jets. Part 2. A robust model for unsteady jets
Energy dispersion in turbulent jets. Part 2. A robust model for unsteady jets
复制标题
湍流射流中的能量分散。
DOI：
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复制
发表时间：
2014
影响因子：
3.7
通讯作者：
M. van Reeuwijk
中科院分区：
文献类型：
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作者：
John Craske;M. van Reeuwijk
摘要本文建立了一个包含两种不同类型纵向弥散的非定常湍流射流积分模型。该模型考虑了动量和能量平流速率的差异（I型色散）以及在动量通量突然变化附近发生的速度剖面局部变形（II型色散）。我们采用了Taylor （Proc. R. Soc.）对管道流动中分散的描述。Lond。A, vol. 219, 1953, pp. 186-203)建立非定常射流纵向输运的色散闭合。我们将模型的预测结果与直接数值模拟结果进行了比较，发现两者吻合较好。本文所描述的模型具有较强的鲁棒性，可以用一种简单的中心差分格式进行数值求解。假设射流的纵向速度分布近似为高斯形式，证明了非定常射流在源区固定时保持近似直边。直边性提供了一种代数方法来降低控制方程的阶数，并导致一个简单的平流-色散关系。造成直边性的物理过程是I型色散，它除了决定射流区域的局部响应外，还决定源扰动的增长率。在这方面，高斯分布具有保证直线性和对源扰动不敏感的特殊特征。比高斯分布更尖峰的分布减弱了扰动，并且随着源动量通量的增加（减少），导致射流面积的局部减少（增加）。相反，比高斯分布平坦的剖面放大了扰动，导致射流面积的局部增加（减少）。
Abstract In this paper we develop an integral model for an unsteady turbulent jet that incorporates longitudinal dispersion of two distinct types. The model accounts for the difference in the rate at which momentum and energy are advected (type I dispersion) and for the local deformation of velocity profiles that occurs in the vicinity of a sudden change in the momentum flux (type II dispersion). We adapt the description of dispersion in pipe flow by Taylor (Proc. R. Soc. Lond. A, vol. 219, 1953, pp. 186–203) to develop a dispersion closure for the longitudinal transportation of energy in unsteady jets. We compare our model’s predictions to results from direct numerical simulation and find a good agreement. The model described in this paper is robust and can be solved numerically using a simple central differencing scheme. Using the assumption that the longitudinal velocity profile in a jet has an approximately Gaussian form, we show that unsteady jets remain approximately straight-sided when their source area is fixed. Straight-sidedness provides an algebraic means of reducing the order of the governing equations and leads to a simple advection–dispersion relation. The physical process responsible for straight-sidedness is type I dispersion, which, in addition to determining the local response of the area of the jet, determines the growth rate of source perturbations. In this regard the Gaussian profile has the special feature of ensuring straight-sidedness and being insensitive to source perturbations. Profiles that are more peaked than the Gaussian profile attenuate perturbations and, following an increase (decrease) in the source momentum flux, lead to a local decrease (increase) in the area of the jet. Conversely, profiles that are flatter than the Gaussian amplify perturbations and lead to a local increase (decrease) in the area of the jet.
影响因子：
3.7
作者：
A. Ruban;K. Vonatsos
通讯作者：
A. Ruban;K. Vonatsos