Particle image velocimetry measurement of the wake of a particle with a uniaxial through-hole placed in a uniform flow

As a significant contributor to drag and vibration, the wake created when an object is placed in a fluid flow or moves within a fluid has been extensively investigated. However, studies investigating the effects of through-holes are limited. Therefore, this study addresses this limitation by leveraging three-dimensional particles with uniaxial through-holes, which produce an axisymmetric jet that interacts with the wake in a fundamentally different manner. In this study, the wake behind a particle with a through-hole along its center axis was analyzed using particle image velocimetry in a uniform flow. The particle had a diameter of $d=25.4\mathrm{mm}$, with the through-hole diameter $d_h$ varying by up to 15 mm, corresponding to a diameter ratio $\gamma =d_h/d\le 0.59$. The uniform flow velocity was set to 3.6 m/s, resulting in a Reynolds number of approximately 6000. The results revealed that the flow structure behind the particle was significantly influenced by the diameter ratio $\gamma$. As $\gamma$ increased, the jet flow from the through-hole intensified and surpassed the freestream velocity for $\gamma =0.24,0.35$. The reverse flow region behind the particle decreased with increasing $\gamma$, leading to the formation of distinct vortex structures owing to the interaction between the separated shear layer and through-hole jet. For a smaller $\gamma$, a pair of vortices formed along the separated shear layers and another pair on both sides of the through-hole jet. Conversely, the shear-layer vortices diminished as $\gamma$ increased, whereas the through-hole jet vortices elongated downstream. At $\gamma =0.59$, only the shear-layer vortices remained closely attached to the surface of the particle. These findings offer valuable insights into wake control using through-hole modifications and enhance our understanding of shear layer and jet interactions in bluff-body wakes.