A gas turbine engine, including: a plurality of blades (60) assembled into an annular row of blades and partly defining a hot gas path (26) and a cooling fluid path (24), wherein the cooling fluid path extends from a rotor cavity (22) to the hot gas path; an angel wing assembly (99) disposed on a side (74) of a base (76) of the row of blades; and pumping features (130) distributed about the angel wing assembly configured to impart, at a narrowest gap (42) of the cooling fluid path, motion to a flow of cooling fluid flowing there through. The plurality of pumping features, the angel wing assembly, and the base of the row of blades are effective to produce a helical motion to the flow of cooling fluid as it enters the hot gas path.