Parameters defining flow resistance and the friction factor behavior in liquid annular seals with deliberately roughened surfaces

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Title: Parameters defining flow resistance and the friction factor behavior in liquid annular seals with deliberately roughened surfaces
Author: Villasmil Urdaneta, Larry Alfonso
Abstract: Non -contacting annular seals are internal sealing devices used in rotating machinery , such as multistage centrifugal pumps and compressors . Their design affects both efficiency and rotor stability . Traditional plain and labyrinth seals are being replaced with stators containing different roughness patterns to reduce leakage and enhance rotor response . Several roughened seal experiments with liquid and air have produced leakage data indicating that the friction factor increases as the seal clearance is increased . Simplified models based on bulk flow theory and Moody ? ? ? ? ? ?s approach to characterize wall friction in pipes cannot explain this outcome . This research is an extension of a 2 -D numerical analysis of flat plate experiments with water which found that friction factor of these surfaces is governed by the roughness ? ? ? ? ? ? ability to develop high static pressures . An exhaustive 3 -D numerical analysis of several experiments with liquid annular seals has been performed using a CFD code . Direct numerical simulations (DNS ) of turbulent channel flow and smooth seals were replicated within 1 % using Reynolds -averaged Navier -Stokes (RANS ) equations and turbulence modeling . Similarly , measured groove seal leakage rates were reproduced within 2 % . On the other hand , no turbulence model combination predicts the leakage in most 3 -D pattern roughened seals with the same accuracy . Present results reproduce the friction factor ? ? ? ? ? ?plateau ? ? ? ? ? ? behavior predicted with the 2 -D analysis and observed in the flat plate experiments . They also reproduce the friction -factor -to -clearance indifference behavior , the maximum friction factor observed in a specific roughness pattern size is independent of the actual clearance in a certain Reynolds number range , but clarify the role of the roughness length -to -clearance ratio and the actual roughness size in defining the friction -factor -toclearance proportionality . All simulations indicate that roughened surface area and roughness aspect ratios are the parameters defining the friction factor at a given seal clearance . The roughness pattern size , relevant in determining the friction -factor -to -clearance proportionality , plays a moderate role once the above cited ratios are defined . In any shape and size , shallow patterns are predicted and observed to provide larger friction factors than deep patterns . Predictions also confirm limited experimental data showing that friction factor is affected by the mean flow orientation relative to the roughness pattern . Solving RANS equations is sufficient to model simple seal geometries but might not be enough to replicate turbulent flow in liquid annular seals with roughened surfaces .
URI: http : / /hdl .handle .net /1969 .1 /4262
Date: 2006-10-30

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Parameters defining flow resistance and the friction factor behavior in liquid annular seals with deliberately roughened surfaces. Available electronically from http : / /hdl .handle .net /1969 .1 /4262 .

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