Development of Two-Focus LDV System for Analysis of Spatial Structure of Turbulence

用于湍流空间结构分析的双焦点 LDV 系统的开发

• 批准号: 06555061
• 负责人: KIDO Hiroyuki
• 金额: $ 6.53万
• 依托单位: KYUSHU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06555061/
• 关键词: LVD; Turbulence; Turbulence Length Scale; Cross-correlation Function of Turbulence; 2焦点LDV; 乱れ場

Turbulent flame structure has large influences on the turbulent burning velocity. Not only turbulence intensity but also turbulence length scales are very important factors to turbulent flame structure. In the many past studies, turbulence length scales were estimated by the Taylor's hypothesis using mean velocity and turbulence time scale obtained from auto-correlation function of turbulence. Turbulence length scales are by definition obtained from cross-correlation of turbulence. In this study, Two-Focus LDV System was developed in order to obtain turbulence length scales by definition. This LDV (Laser Doppler Velocimetry) system has two measuring volumes. Velocities at two points are measured at the same time. The separation distance between two measuring points is able to be changed perpendicularly to the measuring velocity vector. Cross-correlation function of turbulence is obtained by this LDV system changing the separation distance. This system was applied for turbulent flow fields in the wind tunnel and cnstant volume bomb. And the following conclusions were obtained. (1) Velocity measurement is possible even at the separation distance 0.5mm. (2) Integral length scale obtained by this system is rather different from the estimated one from Taylor's hypothesis, though this comparison was carried out in the wind tunnel where the mean velocity is 8 times of turbulence intensity. (3) Turbulence length scale can be obtained by this system even in the flow fields where no mean flow exists and Taylor's hypothesis is not applicable.

湍流火焰结构对湍流燃烧速度有很大的影响。湍流强度和湍流长度尺度是影响湍流火焰结构的重要因素。在以往的许多研究中，湍流长度尺度是由湍流自相关函数得到的平均速度和湍流时间尺度通过泰勒假设来估计的。根据定义，湍流长度尺度是从湍流的互相关获得的。本研究开发了双焦点激光多普勒测速系统，以获得湍流长度尺度。该LDV（激光多普勒测速）系统有两个测量体积。同时测量两点的速度。两个测量点之间的间隔距离能够垂直于测量速度矢量而改变。通过改变激光多普勒测速系统的间距，获得了湍流的互相关函数。该系统已应用于风洞和定容弹的湍流流场测量。并得出以下结论。(1)即使在0.5mm的分离距离下也可以进行速度测量。(2)虽然是在平均风速为8倍湍流强度的风洞中进行的，但该系统得到的积分尺度与Taylor假设的积分尺度有较大的差异。(3)即使在不存在平均流和泰勒假设不适用的情况下，该系统也能获得湍流长度尺度。