Experiments and numerical simulations are conducted for an array of axial-flow Marine Hydro-Kinetic (MHK) turbines operating in a flume. This study aims to understand the influence of coherent structures in high Reynolds number wakes on energy extraction and dynamical rotor control processes. In the flume experiments, rotor torque and rotational position measurements are collected, and the flow field is characterized by simultaneous imaging with particle image velocimetry. The performance of 3 turbines are characterized under varying stream-wise spacing and cross-stream offsets. To study the effect of unsteady hydrodynamics, the turbines are outfitted with either open-loop or close-loop feedback rotor-speed controller. In the numerical simulations, turbine models within the class of "actuator methods" are included from LargeEddy-Simulations and Reynolds-Averaged-NavierStokes methods, where these turbine models impose body forces upon the flow field in form of disks or lines.