When two horizontal rotors are put side-by-side, with slight gaps between them (less than two diameters), the flow velocity near the centerline is higher than the free stream. In this paper, we employ experimental and computational methods to examine the turbulent wake flow of a single turbine, the interactions between two side-by-side rotors, and the power output of a turbine inside a triangular arrangement (with two rotors upstream and one downstream). The experiments are carried out in a wind tunnel using 1:10 scale models. The wake flow is characterized by applying the hot-wire anemometer. Numerical simulations are employed to characterize a single turbine’s near-wake flow and guide side-by-side rotor investigations. The results demonstrate that more power can be converted by a group of three horizontal axis turbines arranged in a triangular frame than by three separate turbines. We show that the RANS turbulence model accurately computes mean velocity but not Turbulence Intensity (TI). We propose a new URANS post-processing approach that improves TI calculations at the wake region. Our findings suggest that wind, tidal current, and hydrokinetic farms may be able to convert more power adopting triangular arrays than they can in standard aligned or staggered row designs.