Multi-element airfoil for pulp screens

A pulp screening apparatus comprising a substantially cylindrical screen having a cylindrical axis, a foil, means for mounting said foil for rotation on said cylindrical axis, said foil having a leading foil section and a trailing foil section, said leading foil section leading in a direction of movement of said foil as it is rotated around said cylindrical axis and said trailing section spaced from and trailing said leading section in said direction of movement to provide a space separating said a trailing end of said leading foil section and a leading end of said trailing foil section and defining a passage for fluid, each of said foil sections having a high pressure side facing away from said screen and a cambered low pressure side facing and positioned adjacent to said screen, said pressure surface of said leading foil section adjacent to said trailing end of said leading foil section having a portion adjacent to which said leading end of said trailing foil section is positioned so that a surface of said portion of said pressure face on said leading foil section and an adjacent surface of said leading end of said trailing foil section define opposite walls of said passage, said high pressure side of said leading foil section, said opposite walls of said passage and said cambered low pressure side of said trailing foil section being relatively positioned so that fluid passing across said high pressure side of said leading foil section passes through said passage and along said cambered low pressure side of said trailing section, said foil being set at a first angle of attack (α) and said trailing foil section being set a second angle of attack (θ).