平面射流沿轴线的特征尺度及其对测量信号过滤程度的依赖

Centerline characteristic scales of a turbulent plane jet and their dependence on filtration of measured signals

对出口雷诺数约为13000的湍流平面射流瞬时速度(u)测量信号(um)进行高频过滤研究.在分析了高频噪声对u测量精度的影响后,使用Mi等人(2005,Phys.Rev.E71,066304)提出的快速收敛迭代法对um进行了数值过滤,并考察过滤前后统计湍流量的变化.结果发现,噪声的存在不仅对湍流小尺度统计量的估算影响显著,也对与大尺度关联的量产生一定的影响.在有效去除噪声造成的误差后,本文正确地获得了典型湍流特征尺度Kolmogorov微尺度、Taylor微尺度和积分尺度沿平面射流中心线的变化规律.这些特征尺度在经历下游距离约为20倍矩形喷嘴短边边长的发展后,开始呈现随下游距离的线性变化规律,即逐渐进入湍流自保持状态.湍流小尺度统计量比大尺度统计量能更快地发展到自保持状态.

This study has two main objectives：（1） to examine the availability of a filtering scheme developed by Mi et al（2005,Phys.Rev.E 71,066304） on the measured velocity signal and（2） to investigate the centerline characteristic scales of a plane jet with the exit Reynolds number of Re = 13188.The success of the filtering scheme has been well validated.It is found that the existence of the high-frequency noise impairs not only the small-scale properties of turbulence but also those associated with large-scale turbulence.After filtering the noise,while the dissipation rate of turbulence kinetic energy is correctly obtained,the characteristic scales of turbulent flow（i.e.the Kolmogorov and Taylor turbulence micro-scales and the integral scale） are appropriately estimated.The results reveal that the centerline characteristic scales of the plane jet exhibit a linear dependence on the downstream distance（x） at x ≤ 20 h,where h is the height of the nozzle.It is interesting to note that the statistical properties of small-scale turbulence appear to enter their self-preserving state earlier than those of large-scale turbulence in the jet.To our knowledge,this finding has not been reported in the literature.