Experimental study on the large-scale turbulence structure dynamics of a counterflowing wall jet

The dynamics of the vortex structure in a three-dimensional, round counterflow wall jet are investigated using particle image velocimetry (PIV) to explore the large-scale turbulence structure and to analyze the mechanism of its generation in the flow field. The ratio of the jet velocity to the main flow velocity is 8.89, and the Reynolds number based on the diameter of the jet pipe is 9127. Typical vortex structures are detected in the stagnation region and main flow by the virtual dye method. The instability of the jet shear layer is caused by the feedback mechanism. The vortex ring is formed while the jet is fluttering upwards. Fluid flows from the recirculation region to the original location of the vortex ring. The main flow analysis reveals the growth process of the front vortex until its break-up. The angle of the relevant streamwise velocity fluctuation region experiences a relatively large deflection between x/D = 40 and x/D = 50 due to the action of the main flow. The turbulent kinetic energy contribution of the wall-normal component is particularly significant in the recirculation region. Furthermore, dynamic mode decomposition (DMD) analysis exposes three low-frequency modes. The first mode corresponds to the stretching and contraction of the jet in the streamwise direction. The second mode has two dynamic characteristics: the fluctuation of the wall-normal direction of the recirculation region and the fluctuation of the center of the recirculation region along the streamwise direction. The third mode is also characterized by fluctuations in the streamwise direction in the center of the recirculation region.