Numerical and Experimental Analyses of Dynamic Characteristics for Liquid Annular Seals with Helical Grooves in Seal Stator

[+] Author and Article Information
Keisuke Nagai

Kamitomioka-machi 1603-1, Nagaoka-shi, Niigata, 940-2188 Japan

Satoru Kaneko

Kamitomioka-machi 1603-1, Nagaoka-shi, Niigata, 940-2188 Japan

Hiroo Taura

Kamitomioka-machi 1603-1, Nagaoka-shi, Niigata, 940-2188 Japan

Yusuke Watanabe

Honfujisawa 4-2-1, Fujisawa-Shi, Kanagawa 251-8502 Japan

1Corresponding author.

ASME doi:10.1115/1.4039428 History: Received May 02, 2017; Revised November 12, 2017


Numerical and experimental analyses were carried out to investigate the dynamic characteristics of liquid annular seals with helical grooves in the seal stator. As with our previous study on static characteristics, in the numerical analysis, the governing equations were the momentum equations with turbulent coefficients and the continuity equation, all averaged across the film thickness and expressed using an oblique coordinate system. The numerical analysis included the effect of both fluid inertia and energy loss at the step between the land section and the helical groove section. In the experiments, for helically grooved seals with different groove helix angles, the dynamic fluid-film pressure distributions, which were induced by a small whirling motion of the rotor about the seal center, were measured to obtain the dynamic fluid-film forces, dynamic coefficients, and whirl-frequency ratio. The equivalent numerical results relatively agree well with the experimental results, demonstrating the validity of the numerical analysis. The value of the tangential dynamic fluid force decreased with increasing the helix angle ?. As a result, the values of the cross-coupled stiffness coefficient Kc and the whirl-frequency ratio WFR (= Kc/(Cm?), where Cm is the main damping coefficient and ? is the angular velocity of the rotor spinning) decreased with increasing ? and became negative for sufficiently large ?. In general, pump rotors rotate with a forward whirling motion under normal operating conditions. Hence, the negative value of WFR contributes to rotor stability by suppressing the forward whirling motion of the rotor.

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