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 . <EOS>