Effects of tooth bending damage on the leakage performance and rotordynamic coefficients of labyrinth seals

Tooth bending damage resulting from an intense impact by the rotor sometimes occurs in the transient operation.To investigate the influence of after-damage clearance and tooth bending length on the leakage performance and rotordynamic coefficients of labyrinth seals,three tooth bending damages were taken into consideration,including the unbent tooth damage(abbreviated as Unbent),the partial tooth bending damage(abbreviated as Pbent)and the complete tooth bending damage(abbreviated as Cbent).The transient CFD solution was utilized to calculate the leakage flow rates and rotordynamic coefficients of labyrinth seals with clearances of 0.3,0.4,0.5,0.6 mm for three tooth bending damages.The obtained result shows that the Unbent tooth damage leaks least while the Pbent tooth bending damage leaks most,and an increase of 6.1%for Cbent tooth bending damage and an increase of 19.4%for Pbent tooth bending damage are discovered at the tooth clearance of 0.6 mm in comparison with the Unbent tooth damage.Compared to the Unbent tooth damage,the effective damping for Pbent tooth bending damage and Cbent tooth bending damage is lower and drops by 9.7%–33.6%and 8.5%–22.6%respectively at the tooth clearance of 0.6 mm,suggesting that Pbent tooth bending damage or Cbent tooth bending damage tends to weaken the seal stability when compared to the Unbent tooth damage.

An Analytical Method to Detect the Coupling Damage Relationship of Concrete Subjected to Bending Fatigue and Temperature Actions

Based on the assumptions validated by the experiments,an analytical method to detect the coupling actions of bending fatigue and temperature on concrete was proposed.To this purpose,a coefficient denoted by f D （T）with the strain distributions caused by these two actions was defined.In terms of the known parameters and the fitted functions of strain,the explicit expression for f D （T）which develops in the way same as the law of temperature change in the body of specimens was obtained.Our experimental results indicate that the weigh fraction of temperature stress decreases in the coupling damage field with the fading temperature gradient,and consequently disclose the mutual influence between these two types of actions in the loading history.