Abstract

The paper deals with the laminar florw through a flat-wall face clearance with a variable width betwen the stationary and rotating rigs. The flow through such a clearance with immobile walls is described, too. Besides the longitudinal clearance, the face clearance is an essential structural element of hydraulic machines. A characteristic example is the face clereance between the slip and stopper ring the balance disk in a multistage centrifugal pump. In the case of conventional solutions of the balance disc the structionally required width of the clearance leads to a turbulent flow of the liquid through the clearance [2]. If the outer diameter of the balance disk is reduced, the pressure under the disk increases, the width of the face clearace gets smaller and the flow rate through this clearance become less intensive. In result, the turbulence of the flow drops and it becomes possible to enter the zone of transient and laminar flows [7]. The reduction of the diameter of the balance disc is connected with a reduction of leakage losses and friction resistance, and thus the pump becomes more efficient. In the case of apllying a self-aligning disc, the momentum of the pressure forces may deviate it, preventing a dry friction of the slip-ring against the stopper ring. Such a disk can operate with a considerably narrower clearance than that required by stiff discs. Laboratory-scale investigations carried out on a model of a balance disc with a self-aligning support of the rotating ring have confirmed that in the case of the centrifugal flow the distribution of pressure in the force clearance prevents the occurrance of dry friction, i.e. a contact of both rings [7, 8]. In conventional structures of balance discs this effect is neutralized by their stiffness, so that the possibility of dry friction cannot be prevented.