论文标题
湍流流动中粘度变化的影响
The effect of varying viscosity in turbulent channel flow
论文作者
论文摘要
在本文中，我们检查了在流向方向上的粘度在空间上变化的粘度。雷诺数是在本地施加的，并使用三个不同的坡道。该设置让人联想到瞬态通道流，但具有空间依赖性粘度而不是时间依赖性粘度。它也与核工程中的各种应用有关，尤其是在测试反应堆中，粘度在流向方向上发生了明显变化，并且在这些条件下，严重缺乏直接数值模拟（DNS）数据来基准测试湍流模型。 作为这项工作的一部分，我们设置了一个新颖的基准案例：该通道沿流方向扩展到20便士。在第一个4p区域，粘度保持恒定。该入口区域被用作循环区域，以在坡道区域的开头获得完全开发的流量。在坡道区域中，雷诺数沿通道线性增加。该流量在跨度方向上是同质的，而在河流正常方向上则是非孔子的。我们在此处使用NEK5000（在Argonne National Laboratory开发的光谱元素计算流体动力学（CFD）代码）内执行直接数值模拟（DNS）。 在这项研究中，具体的重点是研究沿流动方向近壁区域中湍流特性和结构的研究。收集和研究湍流统计。与瞬态通道流相似，结果表明，跨通道的雷诺的变化不会导致坡道区域中湍流结构大小的立即变化，并且实际上在壁剪和摩擦雷诺数中都观察到延迟。将本研究的结果与文献中有关摩擦速度的相关性和雷诺数的函数进行了比较。
In this article we examine channel flow subject to spatially varying viscosity in the streamwise direction. The Reynolds number is imposed locally with three different ramps. The setup is reminiscent of transient channel flow, but with a space dependent viscosity rather than a time dependent viscosity. It is also relevant to various applications in nuclear engineering and in particular in test reactors, where the viscosity changes significantly in the streamwise direction, and there is a severe lack of Direct Numerical Simulation (DNS) data to benchmark turbulence models in these conditions. As part of this work we set up a novel benchmark case: the channel is extended in the stream-wise direction up to 20p. The viscosity is kept constant in the first 4p region. This inlet region is used as a cyclic region to obtain a fully developed flow profile at the beginning of the ramping region. In the ramping region the Reynolds number is linearly increased along the channel. The flow is homogenous in the spanwise direction, while it is nonhomogenous in the stream-wise and wall-normal direction. We perform here Direct Numerical Simulation (DNS) with Nek5000, a spectral-element computational fluid dynamics (CFD) code developed at Argonne National Laboratory. In this study, specific focus is given to the investigation of turbulence properties and structures in the near-wall region along the flow direction. Turbulent statistics are collected and investigated. Similarly to transient channel flow, the results show that a variation in the Reynolds across a channel does not cause an immediate change in the size of turbulent structures in the ramp region and a delay is in fact observed in both wall shear and friction Reynolds number. The results from the present study are compared with a correlation available in the literature for the friction velocity and as a function of the Reynolds number.
