Bulk-flow model for the transition to turbulence regime in annular pressure seals
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abstract
An analysis for the prediction of the dynamic force response for annular seals in the transition regime to flow turbulence is presented. A heuristic curve fit connects the laminar friction factor to Moody's turbulent 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-order) governing the flow for small amplitude rotor motions about an equilibrium position. General equations are presented for the shear coefficients and their derivatives required in the bulk-flow model. Flow rates, drag torque and rotordynamic force coefficients are compared with those from traditional analyses for an annular seal experiencing wear and increased clearances leading to off-design operating conditions. Predicted seal force coefficients show physically sound, smooth variations while passing through the transition zone and demonstrate a marked improvement over simpler models which predict sharp discontinuities. 1996 Taylor & Francis Group, LLC.
