The Effects of Converging and Diverging Axial Taper on the Rotordynamic Coefficients of Liquid Annular Pressure Seals: Theory Versus Experiment

Abstract

Experimental results are compared to predictions for turbulent flow, short (D=76.2 mm,L/D=.17), smooth annular seals with converging and diverging axial taper. Results are presented for four geometries with the same minimum clearances: two convergent, two divergent, and a constant-clearance. Measurements were taken at seal pressure differentials and shaft rotation rates ranging from 1.34 to 3.54 MPa and 10,200 to 24,600 rpm, respectively. Measurements parameters include leakage, direct stiffness, cross-coupled stiffness, and direct damping coefficients. Results show that direct stiffness generally increases with converging axial taper and decreases with diverging axial taper; however, direct stiffness decreases in the first increase in the taper angle, contrary to predictions. Direct damping and cross-coupled stiffness were shown to decrease with increasing convergent or divergent taper. Measured damping values increase with increased running speed and decreasing average clearance. Theoretical predictions for rotordynamic coefficients are in reasonable qualitative agreement with measured results. The theory consistently underpredicts leakage by ranges of 10∼30 percent. The accuracy of predictions for leakage and rotordynamic coefficients was not influenced by running speed. [S0739-3717(00)70102-4]