We employ interface-resolved direct numerical simulations of a dense suspension in turbulent channel flow laden with finite-size spherical particles at a high solid volume fraction of $\mathrm{\Phi }=0.2$. By systematically varying particle diameters ($a/h=1/12,1/18,1/24$) and density ratios (${\rho }_r=0.5,1,10$), we show that low-inertia particles homogenize flow topology across wall-normal regions by generating symmetric vortex stretching and biaxial strain at the particle–fluid interface, recovering a uniform “tear-drop” shape in the joint probability density functions of the invariants $Q$ and $R$. With increasing inertia, this homogenization weakens first in the viscous sublayer and the buffer layer since heavy particles cannot follow small-scale vortices; their wakes break the symmetry in $Q–R$, fragmenting the classical energy cascade. High-inertia particles preferentially cluster in the channel core, suppress near-wall sweep or ejection events, flatten vortex cores, elevate drag by amplifying particle-induced stresses while reducing both Reynolds and viscous stresses; meanwhile, near-wall turbulent kinetic energy is enhanced by localized intense shear. These results bridge interphase interactions and bulk modulation and quantify how particle inertia reorganizes turbulent structures in dense suspensions.

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• Particle-laden flows
• Direct numerical simulations
• Immersed boundary methods
• Lagrangian particle tracking