Effect of critical-inertia particles on the wake breakdown and downwash suppression of a transonic rotor

The influence of particle inertia on interphase momentum transfer and coherent wake breakdown for a transonic rotor in a low-density particle-laden flow is investigated using Delayed Detached Eddy Simulation (DDES) coupled with an Eulerian–Lagrangian Discrete Phase Model (DPM). The rotor operates at Matip = 0.94, and five monodisperse particle sizes from 1 to 100 μm are examined. The aerodynamic response depends non-monotonically on the particle Stokes number (St). Among the sampled sizes, the 10 μm case (St = 2.4) produces the strongest wake modulation, whereas the 100 μm ballistic-like case remains close to the clean-flow baseline in the integral loads and vortex circulation. At z/R = 0.4, the normalized plane-integrated particle mass-flux index reaches 5.2 for the 10 μm case, while the normalized tip-vortex circulation decreases from 0.891 in the clean flow to 0.384, a reduction of 56.9%. This wake attenuation is consistent with reduced coherent downwash over the outer rotor region and coincides with a maximum local sectional thrust increase of 34.8% at r/R = 0.85; the corresponding increase in the time-averaged total rotor thrust is 26.4%. The thrust spectrum changes from discrete blade-passage harmonics toward broadband fluctuations, with the broadband level increasing by up to approximately three orders of magnitude. The peak total local entropy generation rate is 978.29 W m−3 K−1; turbulence-related dissipation and interphase drag contribute 52.0% and 33.2%, respectively. These results establish, for the investigated conditions, a mechanism-based relationship among particle relaxation, preferential concentration, wake attenuation, sectional-load redistribution, spectral broadening, and local irreversible dissipation within a unified DDES-DPM framework.