Measurements of velocity and concentration in a high Reynolds number turbulent boundary layer

Abstract

Measurements of velocity and concentration fluctuations for a horizontal plume released at eight different heights within a turbulent boundary layer (TBL) are discussed in this paper. Most previous studies have reported measurements for the source height limited to s z / δ ≤ 0 . 2 ( s z is the source height and δ is the boundary layer thickness). Here we examine concentration fluctuations when the plume is released in the logarithmic and outer regions of a TBL in order to understand the role of large-scale structures in the transport of scalar quantities. The wall-normal distributions of mean and vari-ance of concentration fit well with the reflected-Gaussian model as previously reported by Fackrell & Robins (1982). A comparison of autocorrelation functions reveals that the integral time scale of the corresponding concentration fluctuations is approximately ten times smaller than the integral time scale of streamwise velocity. Further, it is observed that streamwise scalar flux and cross-correlation coefficient between large-scale velocity and concentration have similar behaviour, i.e., they are positively correlated below and negatively correlated above the plume centreline.