Experimental study on near wake shedding structure of pyramid roughness element in liquid–solid two-phase turbulent boundary layer

Abstract

Particle image velocimetry (PIV) on the liquid–solid turbulent boundary layer containing solid particles with an average diameter of 355 μm is used to study the shedding structure near-field of the pyramid with varied yaw angle values (0°, 15°, 30°, and 45°). We find that the recirculation zone grows larger with increasing value by comparing the average velocity field and turbulence intensity at various angles. When closed vortex lines develop behind the pyramid at about (h, 0.8 h), the center of the recirculation zone gradually stabilizes; in the meantime, the turbulence intensity rises relative to the small α values. Power spectral density function (PSD) and proper orthogonal decomposition (POD) are used to analyze the near-field. According to the findings, various values have an impact on wake shedding structures. At the top and base of the pyramid, shearing vortices occur simultaneously on a regular basis, and their incidence is sensitive to variations in α. Similar top shedding structures are observed at various angles in the POD results. Furthermore, with increasing α, the reattachment vortex is observed at the downstream edge of the pyramid. We study the behavior and statistical properties of particles at various positions, and our findings suggest that the upper flow field's particle concentration distribution dispersion is greater than that of the wake. Some particles from the vicinity of the pyramid is attracted into the wake's recirculation zone and is carried downstream by the shedding vortex.