Multiple hydrokinetic turbines in three array configurations were characterized computationally by employing Reynolds Averaged Navier-Stokes equations. The simulations were conducted for pre-existing turbines operating at their optimum power coefficient of 0.43 which was obtained by design and optimization process. Mechanical power for two adjacent units was predicted for various lateral separation distances. An additional two-by-two turbine array was studied, mimicking a hydro-farm. Numerical simulations were performed using actual physical turbines in the field rather than using low fidelity models such as actuator disk theory. Steady state simulations were conducted using both Coupled and SIMPLE pressure-velocity solvers. Steady three dimensional flow structures were calculated using the k-omega Shear Stress Transport (SST) turbulence model. At a lateral separation distance of 0.5D(t), the turbines produced an average 86% of the peak power a single turbine producing. Interaction effects at lateral separation distances greater than 2.5D(t) were negligible. The wake interaction behind the upstream turbines causes a significant performance reduction for downstream turbines within 6D(t) longitudinal spacing. Downstream turbines employed for the present study performed around 20% or less of a single unit turbine performance for the same operating conditions. Downstream turbines yielded comparable reductions in power to that of experimental results. (C) 2016 Elsevier Ltd. All rights reserved.