The effect of non-uniform inlet flow temperature and pressure conditions due to stator/rotor interaction and supplementary steam on fluid excited rotordynamic characteristics of blade tip labyrinth seal was numerically investigated by unsteady Reynolds-averaged Navier-Stokes(URANS)solution based on the multi-frequency elliptical orbit rotor whirling model and dynamic mesh technique. The rotordynamic coefficients of blade tip labyrinth seal were calculated at three different inlet preswirl ratios of 0.2
0.5 and 0.7. The rotordynamic characteristics of the blade tip labyrinth seal were comparatively analyzed under the conditions of non-unif
orm and uniform inlet flow temperature and pressure. The obtained results show that the increasing inlet preswirl ratio weakens rotor stability of labyrinth seal; the discrepancies of the circumferential swirl strength and pressure under non-uniform inlet and uniform inlet conditions are gradually reduced with the increasing inlet swirl ratio
and the differences of rotordynamic characteristics under the two conditions are also reduced when inlet preswirl ratio increases. At least a reduction of 82.7% in cross-coupling stiffness K
xy
an increase of more than 30.7% in cross-coupling damping C
xy
of the blade tip labyrinth seal under non-uniform inlet conditions are observed at inlet preswirl ratio of 0.2 compared with uniform inlet conditions. When inlet preswirl ratio increases to 0.5
the effective damping under non-uniform inlet condition is only 8.4%-12.4% lower than that of uniform inlet condition at whirling frequencies from 50 Hz to 100 Hz. The same rotordynamic coefficients of the blade tip labyrinth seal are captured for the non-uniform and uniform inlet conditions at inlet preswirl ratio 0.7
so the effect of the inlet flow condition on the rotordynamic characteristics can be omitted at higher inlet preswirl ratio.
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references
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