This study experimentally investigates unsteady flow behavior and coherent structures in T-junctions with a closed branch, employing time-resolved refractive index matched particle image velocimetry (TR-RIM-PIV). The effects of three closed branch depths (L/D= 1, 2, and 4) on flow characteristics were analyzed for both closed straight and side branches at a Reynolds number of 10 000. High-resolution spatiotemporal flow features were captured using TR-RIM-PIV, while proper orthogonal decomposition revealed the energetic flow structures. Phase-dependent variations of these structures were examined to establish correlations between flow dynamics and noise generation. In the closed straight branch configuration (model 1), large-scale vortex structures emerged due to flow separation at both the leading edge and the opposite wall. The downstream shedding of the leading-edge vortex was driven by Kelvin–Helmholtz instability. For L/D= 1, the lateral jet intermittently impacted the rear wall, intensifying pressure fluctuations and converting hydrodynamic energy into acoustic energy. As the cavity depth increased, vortex–wall interactions weakened, resulting in one, two, and three recirculation zones for L/D= 1, 2, and 4, respectively, with decreasing intensity and size. In the closed side branch configuration (model 2), the turning jet adhered to the wall due to the Coanda effect. At the downstream corner, the jet split into two oppositely phased components, forming double-wavepacket structures that intermittently shed and propagated downstream. For L/D= 1, a single clockwise recirculation zone formed. For L/D= 2 and 4, deeper jet penetration produced additional counterclockwise and clockwise recirculation zones.
Li et al. (Mon,) studied this question.
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