  We perform particle-resolved simulations of subsonic and transonic flows past
random arrays of spherical particles. The Reynolds number is held at
$Re{\approx}300$ to ensure the flow remains in the continuum regime. At low
volume fractions, the drag force increases sharply near a critical Mach number
due to the formation of shock waves and reaches a maximum value when the bulk
flow is supersonic. Neighbour-induced hydrodynamic interactions reduce the
critical Mach number at higher volume fractions. An effective Mach number is
introduced to capture the increase in compressibility effects on drag. A new
drag correlation is proposed valid for subsonic and weakly supersonic flow from
dilute to moderately dense suspensions.
