Wake of a Finite-Size Particle in Wall Turbulence Over a Rough Bed

For finite-size particles in turbulence, the particle’s wake causes an additional force on the particle, alters the ambient turbulence and thus changes the properties of the two-phase flow. The mechanism of the interaction between the wake and turbulence, is still ambiguous. Here, we performed fully resolved direct numerical simulations with an immersed boundary method and investigated the wake of a stationary finite-size particle in wall turbulence over a rough bed. We focused on the time-dependent features of the wake, and studied the effect of the ambient turbulence on the wake and the turbulence modulation by the wake. Results show that there exists a strong correlation between the wake and the oncoming turbulent flow, which is beneficial for the precise prediction of the wake-induced force on the particle and the turbulence modulation by the wake. Turbulence augmentation is observed far downstream, while turbulence attenuation region lies near the sphere and the wall where viscous effect is dominant. We also found the effect of roughness is prominent in the near-wall region and is weakened far from the wall. In addition, the vortex shedding happens on only one side of the sphere, and the Strouhal number based on the particle center velocity is around 0.262, about twice that in an unbounded flow. The mechanisms we revealed here provide a basis for building the model of the wake-induced force on a finite-size particle and the turbulence modulation by the particle’s wake.