Design and optimization using computational fluid dynamics to enhance the hydro turbine’s performance are becoming gradually more common because of its flexibility, minor detailed flow description, and cost-effectiveness. These features are not easily achievable in model testing. k–ω simulations conducted in OpenFOAM 7 characterize the flow structure inside an industrial-sized Kaplan turbine module operating at the peak design flowrate. The power signal, velocity, vorticity, and pressure field are presented over the blades and throughout the draft tube. Additionally, pressure fluctuations were probed along the draft tube wall. The simulation shows a tip vortex rope in the narrow gap between the blade tip and turbine casing. The strong influence of the swirl leaving the runner had a negative impact on the flow pressure fluctuation. Also, high vortical activity was presented near the draft tube wall, leading to turbine instability. It was demonstrated that the turbine generates 14.923 MW of average power. The power signal showed minor fluctuations induced by the vortical activity close to the runner region and the corresponding pressure fluctuations. The Fast Fourier Transform showed the system is dominated by low frequency, high amplitude fluctuations.