Unlike the uniform and low turbulence conditions of flow in water tunnels and towing tanks, flow in rivers, channels and oceans is highly turbulent and non-uniform due to the eddies with size that exceeds the diameter of the turbine. This condition accentuates in hydrokinetic farm applications where multiple turbines operate in eddies shed behind the upstream turbines. This data set represents the water tunnel test results of non-uniform inflow and upstream vortices on the quality of the output power and the performance of vertical turbines. The non-uniform flow condition is generated by placing cylinders with different sizes upstream of the turbine. The performance characteristics of the turbine operating behind cylinders are compared to that of the turbine operating in uniform inflow. Cylinders with different sizes are placed upstream of the scaled model turbine at various longitudinal and lateral locations. The effect of non-uniform inflow on the average output power and the instantaneous power fluctuations are presented in this Data set.