Leakage suppression through groove-induced recirculation and prolonged liquid-film persistence in annular plunger seals

Leakage through the confined annular clearance around a plunger is influenced by groove-induced flow restructuring and liquid-film evolution rather than by clearance size alone. Transient volume of fluid simulations under a constant-density–air approximation, together with visualization experiments, were used to examine the effects of periodic grooves on flow separation, local recirculation, reattachment, liquid-phase redistribution, and axial leakage. Within the adopted numerical framework, the grooves divided the continuous high-speed leakage core into repeated separation–recirculation–reattachment regions, generating local low-velocity zones and promoting liquid accumulation within and between the grooves. Groove profile primarily affected the separated-flow path and spatial organization of recirculation, whereas groove width and depth mainly modified their spatial extent. Among the tested configurations, the inverted right-trapezoidal groove produced the best numerical sealing response, reducing liquid leakage by 23.83% and yielding an axial pressure attenuation of 44.77%. High-speed imaging independently showed earlier liquid-film formation, prolonged visible-film persistence, and delayed development of a through-going leakage path. These results associate leakage suppression with local velocity and phase redistribution, liquid retention, and axial-pressure-gradient redistribution rather than geometric blockage alone. The local numerical fields and inclination-angle ranking are conditional on the constant-density formulation, and their robustness under compressible-gas modeling remains to be established.