Time-resolved Tomographic-PIV measurement in the near-wall region of a turbulent boundary layer

The flow in the near-wall region in the turbulent boundary layer has been measured by time-resolved Tomographic-PIV. The resulting instantaneous three-dimensional velocity fields allow visualizing the flow structure in buffer layer or log layer with sufficient spatial resolution of 16×16×16 wall units in a volume spanning 680×170×620 wall units in the streamwise-, wall normal- and spanwise direction respectively. At the measurement location, the thickness of turbulent boundary layer is 71 mm. This corresponds to the Reynolds number based on momentum thickness of 2030. Instantaneous results show the regions of vortical motion detected using the Q-criterion and lowspeed streaks. The distance between low-speed streaks observed in the present experiments is about 100 wall units, which is consistent with earlier experimental studies or numerical studies. In addition, we can visualize vortical motion, such as streamwise vortices, and the autogeneration of a hairpin-like structure. Moreover, the measurement volume extends into the log layer, which enables us to study the effect of the large-scale motions in the log layer passing over the near-wall structures.