The interaction of a dragging, fixed thrust coefficient actuator disk with decaying homogeneous isotropic turbulence (HIT) of varying spatial integral length scales and dissipation rates is studied using Large Eddy Simulation performed at high resolution. Modulation of the turbulence pressure, the deformation of the inflow turbulence as it enters the core, and the wake shear layer turbulence are characterized in detail, and various turbulence quantities pertinent for modeling the problem are reported. The shear layer entrainment (and hence wake recovery) is shown to be strongly sensitive to the integral length scale of the upstream HIT (as opposed to its intensity), and this observation is reconciled using a space-time modal decomposition of the flow field to identify the dominant Kelvin-Helmholtz wavepackets that dictate the shear layer growth rate. © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.