FLUID-STRUCTURE INTERACTIONS IN ANNULAR SEALS OF CENTRIFUGAL PUMPS

Annular seals are used in centrifugal pumps to separate areas of diffe rent pressures. In the fluid gap, motion. dependent interaction (MDI) forces act on the rotor due to relative motion between static and rota ting parts. These fluid-structure-interactions have a decisive influen ce on the rotordynamic properties of the whole system. In order to pre dict the MDI forces, powerful numerical techniques and a new experimen tal method have been developed. The test rig uses active magnetic bear ings to support the rotor and to create defined artificial relative mo tions. For a long annular seal (L/D = 2,0) experimental results are co mpared with calculated results obtained from a finite difference proce dure. Excellent agreement is obtained, especially for coefficients whi ch mainly influence the stability of the component. This validates the accuracy of the developed computer codes. Rotordynamic coefficients g enerated in the eye and the back seal of a 3-D radial impeller are als o calculated. In parallel, measurements of the resultant impeller coef ficients are made. Based on these results, the contribution of the for ces generated in the seals to the total forces generated in the impell er are estimated in order to evaluate the influence of the seals on st ability.