Momentum recovery process in the non-axisymmetric wake of a hydrokinetic turbine at high blockage ratio

Large Eddy Simulation (LES) is used to investigate the wake dynamics of a horizontal-axis hydrokinetic turbine operating at a 35% blockage ratio, significantly higher than in previous wake studies (≤18%). The numerical model was validated against acoustic Doppler velocimeter data from a recirculating flume. The high blockage and non-uniform tip clearances drive non-axisymmetric wake evolution, with the LES model successfully predicting wake recovery length and momentum exchange between the bypass flow and wake. The results demonstrate that the proximity of flume walls alters wake recovery mechanisms in two critical ways: (i) stronger inward turbulent transport immediately downstream of the device, mitigating wake expansion, and (ii) interactions with wall-generated horseshoe vortices that accelerate the break-up of tip vortices, causing an earlier peak in advective and turbulent momentum transport to the wake. For the first time, a momentum budget analysis in confined flow conditions reveals how blockage effects enhance azimuthal advection in the far-wake and induce wake tilting. These findings provide fundamental insights for optimizing turbine arrays in high-blockage environments such as irrigation canals, tailraces, and tidal channels.