PIV measurements on the formation of the flow field and aerosol particle distribution in a turbulent square duct flow

The formation of the flow field and spatial aerosol particle distribution play an important role in various industrial applications. Regarding experiments on aerosol particle transport phenomena in turbulent flows it is of essential interest to generate a homogeneously mixed air stream. Particle Image Velocimetry (PIV) measurements have been conducted in order to characterize the turbulent mixing process in a small-scale gas/aerosol test facility which is designed for the investigation of deposition and resuspension of nuclear aerosol particles. The turbulent flow field in a square duct (Red = 8.9k..43k) is seeded with DEHS droplets in the size range of approximately dPaero = 2 µm. Firstly, the downstream formation of particle mixing is quantified in terms of spatial distribution of scatter light intensity of the PIV images. It is found that sufficient mixing of the aerosol particles is accomplished at 8 to 10 hydraulic diameters downstream of the injection point. Furthermore, the formation of the flow field is evaluated in terms of time mean averaged velocity as well as velocity fluctuations. These values are presented at successive downstream positions and display the development of the turbulent boundary layer. It is shown that the near wall turbulent region of the test section nicely follows the universal slope of a well developed turbulent boundary layer. Nevertheless, the flow field formation still takes place after 20 hydraulic diameters.