The effects of converging and diverging axial taper on the rotordynamic coefficients of liquid annular pressure seals: Theory versus experiment

Experimental results are compared to predictions for turbulent flow, short (D = 76.2 mm, L/D = .17), smooth annular seals with converging and divergin g axial taper Results are presented for four geometries with the same minim um clearances: two convergent, two divergent, and a constant-clearance. Mea surements were taken at seal pressure differentials and shaft rotation rate s ranging from 1.34 to 3.54 MPa and 10,200 to 24,600 rpm, respectively. Mea surements parameters include leakage, direct stiffness, cross-coupled stiff ness, and direct damping coefficients. Results show that direct stiffness g enerally increases with converging axial taper and decreases with diverging axial taper; however, direct stiffness decreases ill 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 t aper. Measured damping values increase with increased running speed and dec reasing average clearance. Theoretical predictions for rotordynamic coeffic ients are in reasonable qualitative agreement with measured results. The th eory consistently underpredicts leakage by ranges of 10 similar to 30 perce nt. The accuracy of predictions for leakage and rotordynamic coefficients w as not influenced by running speed.