Wall-bounded particle-laden flows exhibit a variety of interesting phenomena that can greatly impact the underlying carrier-phase turbulence in practical systems. This work aims at investigating the effects of particle clustering on the carrier-phase turbulence in both dilute and moderately dilute channel flows via highly resolved Euler–Lagrange simulations. It is shown that the fluid turbulence departs significantly from the initially fully developed turbulent flow at moderate concentrations. In particular, the gas velocity retains a viscous sublayer at higher values of mass loading, but displays a strongly reduced boundary layer thickness and a flatter velocity profile compared to the dilute case. Furthermore, the flow orientation with respect to gravity is found to significantly impact the multiphase dynamics. Particles showed a preference to be in the near-wall region with significant volume fraction fluctuations when gravity opposed the mean flow direction, while particles accumulated at the channel center with less significant volume fraction fluctuations for flows with gravity aligned with the mean flow direction.