  Direct numerical simulations of turbulent suspension flows are carried out
with the Force-Coupling Method in plane Couette and pressure-driven channel
configurations. Dilute to moderately concentrated suspensions of neutrally
buoyant finite-size (L_y /d = 20) spherical particles are considered when the
Reynolds number is slightly above the laminar-turbulent transition. Tests
performed with synthetic streaks, in both turbulent channel and Couette flows,
show clearly that particles trigger the instability in channel flow whereas the
plane Couette flow becomes laminar. Moreover, we have shown that particles have
a pronounced impact on pressure-driven flow through a detailed temporal and
spatial analysis whereas they have no significant impact on plane Couette flow
configuration. The substantial difference between both flows is related to the
spatial preferential distribution of particles in the large-scale rolls
(inactive motion) in Couette flow, whereas they are accumulated in the ejection
(active motion) regions in the pressure-driven flow. Through investigation of
particle modification on two distinct flow configurations, we were able to show
the specific response of turbulent structures and the modulation of the
fundamental mechanisms composing the regeneration cycle in the buffer layer of
near-wall turbulence. Especially for pressure-driven flow, the particles
enhance the lift- up and let it act continuously whereas the particles do not
significantly alter the streak breakdown process. The reinforcement of the
streamwise vortices is attributed to the vorticity stretching term by the wavy
streaks. The smaller and more numerous wavy streaks enhance the vorticity
stretching and consequently strengthen the circulation of the large-scale
streamwise vortex in suspension flow.
