A circumferential seal assembly (1 or 21) with, in use, bifurcated flow, said assembly comprising: (a) an annular seal housing (2 or 22) disposed between a pair of compartments (5, 6 or 58, 59); (b) a rotatable runner (15, 35, or 67); (c) a pair of annular seal rings (3, 4; or 23, 24) disposed within said annular seal housing (2 or 22) and disposed about said rotatable runner (15, 35, or 67); and (d) a plurality of groove structures disposed along an outer annular surface of said rotatable runner (15, 35, or 67), each said groove structure includes at least two grooves intersecting a feed groove along said outer annular surface, each said groove structure separates, in use, a source flow communicated into said feed groove so that a portion of said source flow enters each said groove to form a longitudinal flow therein; wherein: each said groove includes at least two adjoining steps whereby each said step is defined by a base wall, said base walls arranged along said groove to decrease depthwise in direction opposite to rotation of said rotatable runner (15, 35, or 67), two adjoining said base walls disposed about a base shoulder, each said base shoulder locally redirects, in use, said longitudinal flow to form an outward radial flow in direction of one said annular seal ring (3, 4; or 23, 24), said base walls bounded by and intersecting a pair of side walls, each said side wall includes at least one side shoulder which narrows said groove widthwise and locally redirects, in use, said longitudinal flow away from said side wall to form a lateral flow in direction of other said side wall, said lateral flow and said outward radial flow being perpendicular to one another and to said longitudinal flow. (a) an annular seal housing (2 or 22) disposed between a pair of compartments (5, 6 or 58, 59); (b) a rotatable runner (15, 35, or 67); (c) a pair of annular seal rings (3, 4; or 23, 24) disposed within said annular seal housing (2 or 22) and disposed about said rotatable runner (15, 35, or 67); and (d) a plurality of groove structures disposed along an outer annular surface of said rotatable runner (15, 35, or 67), each said groove structure includes at least two grooves intersecting a feed groove along said outer annular surface, each said groove structure separates, in use, a source flow communicated into said feed groove so that a portion of said source flow enters each said groove to form a longitudinal flow therein; each said groove includes at least two adjoining steps whereby each said step is defined by a base wall, said base walls arranged along said groove to decrease depthwise in direction opposite to rotation of said rotatable runner (15, 35, or 67), two adjoining said base walls disposed about a base shoulder, each said base shoulder locally redirects, in use, said longitudinal flow to form an outward radial flow in direction of one said annular seal ring (3, 4; or 23, 24), said base walls bounded by and intersecting a pair of side walls, each said side wall includes at least one side shoulder which narrows said groove widthwise and locally redirects, in use, said longitudinal flow away from said side wall to form a lateral flow in direction of other said side wall, said lateral flow and said outward radial flow being perpendicular to one another and to said longitudinal flow.