Leakage and Dynamic Force Coefficients for Two Labyrinth Gas Seals: Teeth-on-Stator and Interlocking Teeth Configurations. A CFD approach to their Performance

[+] Author and Article Information
Tingcheng Wu

Graduate Research Assistant, Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843, USA

Luis San Andres

ASME Fellow, Mast-Childs Chair Professor, Turbomachinery Laboratory, Texas A&M University, College Station, TX 77843, USA

1Corresponding author.

ASME doi:10.1115/1.4041123 History: Received July 13, 2018; Revised July 18, 2018


Labyrinth gas seals (LS) commonly used in turbomachinery reduce secondary flows. LS designs include either all Teeth-On-Stator (TOS) or all Teeth-On-Rotor or an interlocking labyrinth seal (ILS). This paper presents Computational fluid dynamics (CFD) predictions of flow and dynamic force coefficients for an ILS and a TOS LS, both seals sharing identical design features and operating conditions as in an actual compressor. First, CFD predictions are benchmarked against archival test data. Next, CFD mass flow for the ILS is 21% lower than that of the TOS LS, thus demonstrating its efficiency. At a low whirl frequency (?), the TOS LS shows a negative direct stiffness (K<0), frequency independent; whereas the ILS has K > 0 that increases with both frequency and supply pressure. For both seals, |K| decreases when the exit pressure/inlet pressure ratio increases, while the cross-coupled stiffness (k) is frequency dependent, its magnitude increasing with supply pressure. Notably, for both seals, k<0 for ?< rotor speed (O). The direct damping (C) for the TOS LS remains constant for ? > ½ O, having a larger magnitude than that for the ILS for ?'s to 1.5O. An increase in exit/inlet pressures ratio decreases C for both seals. For ?/O < 1.3, the effective damping Ceff=(C- k/?) for the TOS LS is larger than that for the ILS, thus making the ILS not a sound selection albeit it reduces leakage.

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