Research on Local Control of Generation of Quasi-streamwise Vortex in Near Wall Turbulence

近壁湍流中准流向涡产生的局域控制研究

基本信息

批准号：
09450076
负责人：
MIYAKE Yutaka
金额：
$ 8.58万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09450076/
关键词：
Turbulent Flow Turbulence Control Direct Numerical Simulation Wall Turbulence Rough Wall Quasi-Streamwise Vortex Computational Fluid Dynamics Toms Phenomenon 粗面乱流 LES

项目摘要

To obtain an algorithm for a local control of organized structure in the near wall region, we conducted direct numerical simulations for turbulent flows in a plane channel. By adding some modifications, we observed the modulation of the vortex structures in the near wall region.By the spanwise oscillation of the wall, the transform of vorticity from spanwise to streamwise components was prevented. It resulted in the significant decrease in the generation of streamwise vortices.For the wall roughness, we considered sand-like roughness and ribs. The streamwise vortices in the near wall region was replaced by the typical structure depend on the roughness features. In the outer region, however, the global scale of flow passage characterized the turbulence structure.By increasing the viscous resistance especially in the spanwise direction the significant decrease in hydrodynamic drag was attained. The mass flow rate was increased by the addition of such an anisotropic viscosity only in the vicinity of the wall such as within the buffer layer, for both high and low Reynolds numbers.To mimic the drag reduction by adding a small amount of polymers, a direct numerical simulation was carried out, in couple with discrete element models. The polymer in the turbulent flow is represented by beads-spring-dashpot element. The viscosity represented by a dashpot is found to be the primary factor for the drag reduction. Experimental findings were reproduced consistently in our simulation.On the basis of the above-mentioned numerical experiments, we confirmed that the control of quasi-streamwise vortices was effective for the modification of wall bounded turbulence.

为了获得近壁区域组织结构的局部控制算法，我们对平面通道中的湍流进行了直接数值模拟。通过添加一些修改，我们观察到近壁区域涡结构的调制。通过壁的展向振荡，阻止了涡度从展向分量向流向分量的转变。这导致流向涡的产生显着减少。对于壁面粗糙度，我们考虑了沙状粗糙度和肋状粗糙度。近壁区域的流向涡被依赖于粗糙度特征的典型结构所取代。然而，在外部区域，流道的整体尺度表征了湍流结构。通过增加粘性阻力，特别是在翼展方向上，实现了水动力阻力的显着降低。对于高雷诺数和低雷诺数，通过仅在壁附近（例如缓冲层内）添加这种各向异性粘度来增加质量流量。为了通过添加少量聚合物来模拟减阻效果，结合离散元模型进行了直接数值模拟。湍流中的聚合物由珠子-弹簧-缓冲器单元表示。发现由阻尼器代表的粘度是减阻的主要因素。实验结果在我们的模拟中得到了一致的再现。在上述数值实验的基础上，我们证实了准流向涡的控制对于壁面有界湍流的修正是有效的。