An insight on the physical mechanisms responsible of power augmentation in a pair of counter-rotating Darrieus turbines

•Detailed analysis on the power augmentation mechanisms in twin counter rotating Darrieus turbines.•Rotor interactions suppress inflow expansion, increase angle of attack, and generate higher lift.•Effects are quantified via AoA calculation through flow sampling.•The power augmentation mechanism is more pronounced at higher tip speed ratios.•Physical insight key to improve multiple Darrieus turbines and tuning low-fidelity methods.