Turbulence in a heated pipe at supercritical pressure
Turbulence in a heated pipe at supercritical pressure
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DOI：
10.1017/jfm.2021.458
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发表时间：
2021-06
影响因子：
3.7
通讯作者：
J. He;R. Tian;P. Jiang;S. He
中科院分区：
文献类型：
--
作者：
J. He;R. Tian;P. Jiang;S. He
摘要本研究的目的是对超临界压力下加热流体流动中的湍流动力学提供一种新的认识。由于热物理性质、浮力和惯性的变化，已经建立了一个统一的解释层状化机制，其中最后一个在发展中的流动中起着重要作用。在新的理解中，各种因素都可以类似地被视为（伪）体积力，其效果是导致所谓的表观雷诺数减少。部分层流由等效压力梯度参考流加扰动流表示。在本文中使用完全层流，指的是没有产生新的旋涡结构的区域。该区域类似于边界层旁路过渡的预过渡区域，并且在这两种情况下，自由流或管芯湍流按指数衰减，但是在边界层中形成细长条纹。由于湍流的衰减以及新产生的条纹，该区域的湍流动能可能仍然很大。后者导致壁面附近的流向速度波动增加。之后，当条纹破裂并产生多尺度涡时，发生再转捩，导致径向和周向速度波动增加。浮力对湍流的结构效应在部分层流中是弱的和负的，但在完全层流和再过渡区中是主导的。
Abstract The purpose of this research is to provide a new understanding of the turbulence dynamics in a heated flow of fluid at supercritical pressure. A unified explanation has been established for the laminarisation mechanisms due to the variations of thermophysical properties, buoyancy and inertia, the last of which plays a significant role in a developing flow. In the new understanding, the various factors can all be treated similarly as (pseudo-)body forces, the effect of which is to cause a reduction in the so-called apparent Reynolds number. The partially laminarising flow is represented by an equivalent-pressure-gradient reference flow plus a perturbation flow. Full laminarisation is used in the paper referring to a region where no new vortical structures are generated. This region is akin to the pre-transition region of a boundary layer bypass transition, and in both cases, the free-stream or pipe-core turbulence decays exponentially, but elongated streaks are formed in the boundary layer. Turbulence kinetic energy in this region may still be significant due to the decaying turbulence as well as newly generated streaks. The latter lead to an increase in streamwise velocity fluctuations near the wall. Later, re-transition occurs when the streaks break down and multi-scale vortices are generated, leading to an increase in the radial and circumferential velocity fluctuations. The structural effect of buoyancy on turbulence is weak and negative in the partially laminarising flow, but is dominant in the full laminarisation and re-transition regions.