Multimodal behavior of turbulent junction flow

This study investigates the unsteady characteristics of turbulent horseshoe vortex in the junction region between a wall-normal wing and a flat plate. To achieve this, the experiment was conducted in planes with 0°, 15°, and 30° polar angles, and velocity fields were measured using particle image velocimetry under ReD=9300 and 37 300. By analyzing these measurements, the statistical and unsteady characteristics of the horseshoe vortex were analyzed. Specifically, backflow, zeroflow, and intermediate modes were identified by conformity of joint probability density function conditional average, and the data-driven proper orthogonal decomposition (POD) modes. The temporal relationship of these flow modes was investigated based on the POD coefficients, and it was statistically indicated that the intermediate mode tends to appear during the transition from the backflow mode to the zeroflow mode. Moreover, the “downwash-incoming flow flux” (ψDI) was defined to analyze the relationship between the flow modes and the velocity field outer of the junction region. It was found that the backflow mode occurs due to a strong near-wall upstream jet caused by downwash, while the zeroflow mode is attributed to high-intensity near-wall incoming fluid.