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 MoodyâÂÂs 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 roughnessâÂÂ
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
âÂÂplateauâ 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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4262 |
| Date | 30 October 2006 |
| Creators | Villasmil Urdaneta, Larry Alfonso |
| Contributors | Chen, Hamn-Ching, Childs, Dara W. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 11347852 bytes, electronic, application/pdf, born digital |
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