Wake dynamics of side-by-side hydrokinetic turbines in open channel flows

Lateral placement of hydrokinetic turbines is an interesting topic, as the blockage effect can increase the flow speed and increase the power coefficient (CP) for neighboring turbines. This study investigates wake dynamics in hydrokinetic turbine arrays with single- (1T), double- (2T), and triple-turbine (3T) configurations under various tip speed ratios (λ = 3.5, 5.8, and 7.1) using large eddy simulation coupled with the actuator line (AL) model. Results indicate that CP increases as lateral spacing decreases, which highlights the advantages of tighter lateral placement. The CP of the 3T-S turbine (the side turbine in the 3T configuration) is larger than those of the other configurations, following the trend CP,3T−S>CP,3T−M>CP,2T>CP,1T, which reflects a growing blockage effect with more turbines. Wake dynamics are analyzed using time-averaged and instantaneous methods. In 3T scenarios, blockage enhances turbulence kinetic energy, facilitating faster wake recovery, aided by turbine interference. Mean kinetic energy budget analysis shows that 3T-S wakes recover fastest due to increased turbulent convection. For instantaneous analysis, pre-multiplied power spectral density reveals vertical meandering begins at approximately 3D (D is the rotor diameter) and horizontal meandering starts near 4D, with a dominant frequency of St=0.28. Integral length scales show an initial increase followed by a downstream decrease, with minima marking the onset of wake meandering. Dynamic mode decomposition analysis reveals that high-frequency disturbance amplitudes increase with the number of turbines. At the optimal λ, wake effects dominate over inflow effects.