  Direct numerical simulations two-way coupled with inertial particles are used
to investigate the particle distribution and two-way coupling effect of
low-inertia ($St_{LSM}=0.0625$, $St_{VLSM}=0.009$) and high-inertia
($St_{LSM}=0.475$, $St_{VLSM}=0.069$) particles associated with the large-scale
motions (LSMs) and very-large-scale motions (VLSMs) in an open channel flow at
a Reynolds number of $Re_\tau = 550$. One method of filtering the VLSMs from
the flow is via artificial domain truncation, which alters the mean particle
concentration profile and particle clustering due to the removal of VLSMs from
a large domain simulation. In order to exclude possible correlation of the
turbulence introduced by a small domain size with periodic boundary conditions,
low- and high-pass filtering is performed during the simulation to isolate the
particle interaction with different spatial scales. The results show that
particle accumulation and turbophoresis are under-predicted without VLSMs,
whereas the particle clustering and two-way coupling effects are mainly
determined by particle coupling with LSMs. In the inner layer, the elongated
streamwise anisotropic particle clustering can be reproduced by particles
coupling solely with LSMs for low Stokes number ($St_{LSM}=0.0625$) particles.
However, we do not observe similar particle clustering behavior in the outer
layer as seen in the full simulation by coupling particles with either LSMs or
VLSMs for high Stokes number ($St_{VLSM}=0.069$) particles. This indicates that
the organized particle structures are formed by the joint action of LSMs and
VLSMs, especially for high Stokes number particles in the outer layer.
