FLOW VISUALIZATION AND LEAKAGE MEASUREMENTS OF STEPPED LABYRINTH SEALS .1. ANNULAR GROOVE

An improved understanding of a new category of stepped labyrinth seals , which feature a new ''annular groove,'' was obtained. A water leakag e and flow visualization test facility of very large scale (relative t o a typical seal) was utilized. Flow visualization experiments using a new method and digital facilities for capturing and editing digital i mages from an 8 mm video were conducted. The presence of an annular-gr oove machined into the stator land increases the leakage resistance by up to 26 percent for the cases considered here. Tracer particles show the degree of throughflow path penetration into the annular groove (i .e., serpentining), which gives the largest and the smallest leakage r esistance improvement over that of the corresponding conventional step ped seal.