Dye visualization of the wake of a near-wall particle in response to a periodic oscillation

Abstract

In turbulent dispersed multiphase flows, the interaction between the particle wake and the ambient turbulent fluctuation can be crucial for the change of the multiphase system. This issue is extremely complex due to the chaotic nature of the turbulence. In this paper, the ambient turbulent fluctuation of certain frequency is simulated by the Karman vortex street behind a horizontally placed cylinder, and the response of the wake of a stationary near-wall particle to the oncoming oscillation is investigated. The dye visualization is used to mark the vortex structures of the wake and the oncoming oscillation, respectively, and power spectrum analysis is conducted to reveal the features in the frequency domain. Results show that at relatively low Rep, the oncoming oscillation has little effect on the wake. As Rep increases, the response of the wake to the oncoming oscillation is evident. High-frequency fluctuation dissipates very fast and only exists near the particle. On the contrary, the life span of the low-frequency fluctuation lasts for a much longer period and exists far downstream. In addition, the self-induced vortex shedding is not notable and is overwhelmed by the oncoming oscillation.