Results from particle-resolved Direct numerical simulations are presented for dense suspensions of frictional non-colloidal spheres in viscous pressure-driven channel flow. The bulk solid volume fraction varies between \(\phi _b=0.2\) and 0.6, and the Coulomb friction coefficient is either \(\mu _c = 0\) or 0.5. The main objectives are to unravel the influence of (1) \(\phi _b\) and \(\mu _c\) on the flow development time and of (2) heterogeneous shear on the steady-state suspension rheology. Starting from an initially homogeneous distribution, the particles show shear-induced migration toward the core until equilibrium is reached. The flow development time decays exponentially with increasing \(\phi _b/\Phi _R\) , where \(\Phi _R\) is a friction-dependent reference bulk concentration beyond which particle contacts cause a rapid increase in the particle stress. The steady-state rheology is studied by means of the ‘viscous’ and ‘frictional’ rheology frameworks. Excluding the central core and wall regions, the data for the local relative suspension viscosity collapse onto a single curve as function of the normalized local concentration \({\bar{\phi }}/\phi _m\) , where \(\phi _m\) is the friction-dependent maximum flowable packing fraction. The frictional rheology shows ‘subyielding’ at low viscous number \(I_v\) in the core region, where the macroscopic friction coefficient \(\mu \) drops below the minimal value found for homogeneous shear flows. A modified frictional rheology model is presented that captures subyielding. Finally, a model is presented for \({\bar{\phi }}/\phi _{mp}\) as function of \(I_v\) , where \(\phi _{mp}\) is a modified maximum flowable packing fraction. It captures both ‘overcompaction’ in the core beyond \(\phi _{m}\) at high \(\phi _b\) and maximum core concentrations below \(\phi _m\) at lower \(\phi _b\) .
