Leakage and Force Coefficients for Pump Annular Seals Operating With Air/Oil Mixtures: Measurements Vs Predictions and Air Injection to Increase Seal Dynamic Stiffness

LectureThe lecture presents measurements of leakage and dynamic force coefficients for six annular seals operating with an air in oil mixture ranging from pure liquid to just air. Each seal has a distinct clearance configuration: one is a plain seal with a small clearance, and another has a larger (worn) clearance ; a third seal introduces a wavy clearance that produces a significant centering stiffness; a fourth seal has a shallow groove pattern ; and the fifth and sixth seals have a stepped clearance (narrow to wide and wide to narrow). The tests in a plain seal supplied with gas injection (GVF~0?0.6) in the oil stream demonstrate the seal recovers its dynamic stiffness, hence its usage to recover rotor stability. Air injection into a liquid stream drops the mixture sound speed to make it highly compressible; hence the hardening of the seal direct stiffness