Abstract: To reduce profile losses in the aerofoils of low pressure turbines of axial flow reaction turbines, the wake-passing effects on a row of aerofoils downstream of a first row of aerofoils are enhanced by providing a region of roughness on part of the suction surface of each aerofoil of the downstream row. The region of roughness has its leading edge between the location of the geometric throat on the suction surface and a location 75% of the surface perimeter from the leading edge. The region extends over at least 3% of the suction surface perimeter. The use of such a region of roughness is particularly effective in improving the performance of very high-lift aerofoils (coefficient of lift of 1.1 or greater).