An experimental study was conducted to assess fidelity of model-scale representations of full-scale oscillating-foil turbines operating at high Reynolds numbers. The experiments were performed using a NACA 0015 foil with an aspect ratio of 7.5 undergoing controlled oscillations in pitch and heave in a water tunnel. We considered Reynolds numbers ranging from 20,000 to 50,000 to investigate the effects of dynamic stall, channel confinement and forced transition to turbulence using distributed surface roughness. Direct force measurements were used to quantify the performance of the turbine, and quantitative flow imaging was performed using particle image velocimetry. Oscillations of the foil resulted in formation of turbulent boundary layers, particularly in the cases involving the roughened foils. This accelerated transition led to turbine performance characteristics (i.e. efficiency and extracted power coefficient) comparable to those reported for a numerical benchmark case of Re=500, 000.