Experimental study of dynamical characteristics of a long annular seal. Moment due to cylindrical whirl movement.

Abstract

This paper describes the experimental study on dynamic fluid reaction force and moment generated in axially long annular clearance between the rotor and stator of a submerged motor pump or in the balance piston of a turbo pump. For measuring the dynamic fluid force, a test rig was made for having spin and whirl motion of the rotor. In the test, the rotor and the stator were set in concentric conditions and pressure fluctuation, fluid reaction force and flow rate were measured under the basic parameters of rotational speeds and pressure drop across the long seal. In measurement, the moment was obtained from dynamic fluid force and instability threshold (limit) of fluid force was determined. In addition, dynamic fluid force was expressed in terms of the stiffness coefficient, damping coefficient and added mass. It was recognized that moment stiffness coefficient and direct-moement damping coefficient increase with axial flow velocity.