BULK-FLOW MODEL FOR THE TRANSITION TO TURBULENCE REGIME IN ANNULAR PRESSURE SEALS

An analysis for the prediction of the dynamic force response Sbr annul ar seals in the transition regime to flow turbulence is presented. A h euristic curve fit connects the laminar friction factor to Moody's tur bulent friction factor curve in the transition. regime from laminar to fully developed turbulent flows. A universal friction factor model is provided and included in the bulk-flow equations (zeroth- and first-o rder) governing the flow for small amplitude rotor motions about an eq uilibrium position. General equations are presented for the shear coef ficients and their derivatives required in the bulk-flow model. Flow r ates, drag torque and rotordynamic force coefficients are compared wit h those from traditional analyses for an annular seal experiencing wea r and increased clearances leading to off-design operating conditions. Predicted seal force coefficients show physically sound, smooth varia tions while passing through the transition zone and demonstrate a mark ed improvement over simpler models which predict sharp discontinuities .