Probability density function of velocity fluctuations in a rectangular T-junction duct

The streamwise and the spanwise velocity time series are measured from the wall to the centre of the cross duct for the flow in a rectangular T-junction duct, which is similar to airflow conditions of high-speed train ventilation system. The turbulent statistical properties are reported at three streamwise locations which correspond to the upstream/downstream and the centreline of the T-junction (x/D = ±1 and 0, respectively). Turbulence intensities, skewness and flatness factor, as well as probability density functions, have been investigated at the range of Re_τ = 5400–8700. Furthermore, the multiscale properties of the flatness factor are analysed by using orthogonal wavelet transform. It is found that the turbulent intensities remain a constant in the centre region for three streamwise locations while they are weakened in the turbulent boundary layer at x/D = 1 by effect of suction. The location of the strongest intermittency is located at y/h = 0.56 for x/D = −1 and 0. While at downstream of T-junction (x/D = 1), the location of the strongest intermittency shifts down to y/h = 0.28. Also, the wavelet flatness factor is more clearly distinguished the intermittency of the small-scale turbulent structure compared with the conventional flatness factor and, the obtained experimental data are fitted and used to predict the mean streamwise velocity profiles.