CAJ | 학술논문

通过使用一排16根冷线探头排在多个空间点同时测量微加热圆柱的尾流温度场,用小波分析技术对瞬时温度场的时间序列信号进行多尺度分析,目的是研究不同尺度脉动温度对总体温度场的贡献.直径为d=12.7 mm的圆柱产生了被测的尾流,对应的雷诺数为5500,测量区域位于下游距离为2d和20d之间.基于小波多尺度分辨技术,尾流温度场被分解为不同温度脉动特征尺度的小波分量.通过分析这些小波分量的瞬时温度等值线图,能够直接观测到不同特征尺度的涡结构运动特征和湍流间歇过程.特别地,我们在近场区从原始信号分解获得的高频区域中发现了K-H涡的存在.不同尺度的温度方差沿流向的变化表明,在下游距离为x=3d和20d之间,中等尺度的结构比大尺度和小尺度结构对总的温度均方根的贡献更大.不同尺度的自相关函数表明,大尺度和中等尺度的结构显示出较大的相关性,而高频的小波分量则更快地失去了原有的拟序性.
통과사용일배16근랭선탐두배재다개공간점동시측량미가열원주적미류온도장,용소파분석기술대순시온도장적시간서렬신호진행다척도분석,목적시연구불동척도맥동온도대총체온도장적공헌.직경위d=12.7 mm적원주산생료피측적미류,대응적뢰낙수위5500,측량구역위우하유거리위2d화20d지간.기우소파다척도분변기술,미류온도장피분해위불동온도맥동특정척도적소파분량.통과분석저사소파분량적순시온도등치선도,능구직접관측도불동특정척도적와결구운동특정화단류간헐과정.특별지,아문재근장구종원시신호분해획득적고빈구역중발현료K-H와적존재.불동척도적온도방차연류향적변화표명,재하유거리위x=3d화20d지간,중등척도적결구비대척도화소척도결구대총적온도균방근적공헌경대.불동척도적자상관함수표명,대척도화중등척도적결구현시출교대적상관성,이고빈적소파분량칙경쾌지실거료원유적의서성.
@@@@A wavelet multi-resolution technique is applied to analysing the temperature field simultaneously obtained by a rake of 16 cold-wires in the turbulent near-wake of a slightly heated circular cylinder with a diameter of d=12.7 mm in a range of x/d from 3 to 20, where x is the downstream distance from the cylinder axis. This technique enables us to decompose the fluctuating temperature field into a number of wavelet components based on different characteristic frequency bandwidths or scales, which are representative of the temperature fields of different scales. The turbulent mixing characteristics of various fluctuating scales are examined in terms of instantaneous temperature contours of each wavelet component. The flow structures and intermittent processing of various scales are visualized. The streamwise evolutions of temperature variance of various scales suggest that the intermediate-scale structures make larger contribution to the total temperature than the large- and small-scale structures. The wavelet auto-correlation function indicates that the large-and intermediate-scale structures display larger correlation and the wavelet component of higher frequency loses coherence quickly.