摘要
湍流边界层流动精细涡结构的分析对于水下航行体表面减阻乃至降噪机理的深入研究都具有重要意义。文章应用粒子图像测速技术(PIV),对Re_θ=1 743和5 400时的平板湍流边界层的流向一法向平面流场进行了测试研究。一方面,直接对瞬时速度场精细涡结构进行提取分析,通过Galilean分解和λ_(ci)准则识别出流向—法向平面中的发卡涡及发卡涡包。研究表明,发卡涡和雷诺应力的分布特征具有高度相关性;发卡涡包产生了流向动量的法向不规则分层分布特征。另一方面,文中通过对500个瞬时速度场子样进行时间平均分析,获得了不同雷诺数下平均速度以及湍流度分量的法向分布规律。此外,文中还对发卡涡的几何尺寸和漩涡强度λ_(ci)进行了统计分析。研究表明,在y^+<50范围内无量纲化的漩涡强度λ_(ci)δ/u_τ沿法向迅速衰减,且在不同雷诺数下变化曲线基本一致;在y^+>50后λ_(ci)δ/u_τ衰减平缓,且低雷诺数下的值较大。
The analysis of detailed flow structure of a turbulent boundary layer is of great significance for deeper research of the drag and noise reduction mechanism.The instantaneous velocity field in a streamwise-wall-normal plane of a flat plate turbulent boundary layer is measured by using particle image velocimetry technique at Reθ1 743 and 5 400.On one hand,the signatures of the hairpin vortex and packets in the streamwise-wall normal plane is identified and extracted directly from the instantaneous velocity field by the Galilean decomposition and λcicriterion.The results show that hairpin vortex is highly related to the streamwise distribution of Reynolds stress.In addition,hairpin packets produce the normal layered characteristics of the streamwise momentum.On the other hand,The normalized mean streamwise velocity profile and the distribution of turbulent intensity at different Reynolds number are obtained through statistical analysis to 500 instantaneous velocity fields.Moreover,statistical analysis on the geometrical size and swirling strength λciof hairpin vortex is perfromed.Research shows that the normalized swirling strengthλci/uτdecays quickly within y^＋〈50 at both Reynolds number;within y^＋〉50,λci/uτdecreases slowly and is smaller with increasing Reynolds number.
出处
《船舶力学》
EI
CSCD
北大核心
2016年第1期23-30,共8页
Journal of Ship Mechanics
基金
国家自然科学基金项目(51379193)
江苏省自然科学基金项目(BK2012536)
关键词
PIV
湍流边界层
发卡涡
涡包
漩涡强度
涡识别
PIV
turbulent boundary layer
hairpin vortex
vortex packet
swirling strength
vortex identification
