Effect of Honeycomb Seals on Loss Characteristics in Shroud Cavities of an Axial Turbine

The loss in efficiency due to shroud leakage or tip clearance flow accounts for a substantial part of the overall losses in turbomachinery. It is important to identify the leakage loss characteristics in order to optimize turbomachinery. At present, little information is available in the open literature concerning the effect of honeycomb seals on the loss characteristics in shroud cavities of an axial turbine, despite of the widespread use of the honeycomb seals. Therefore, interaction between rotor labyrinth seal leakage flow with and without honeycomb facings and main flow is investigated to provide the loss characteristics of the mixing process of the re-entering leakage flow into the main flow. The effects of honeycomb seals on the flow in shroud cavities and interaction with the main flow are analyzed. An additional study on the impact of subtle shroud cavity exit geometry is also presented. The investigation results indicate that the honeycomb seal affects the over tip leakage flow and reduces mixing losses when compared to the solid labyrinth seal. The leakage flow interactions with the main flow have considerably changed the flow fields in the endwall regions. The proposed research reveals the effects of honeycomb seals on the loss characteristics in shroud cavities and the impact of subtle shroud cavity exit geometry, and it is helpful for the design optimization of turbomachinery.

Numerical investigation on leakage and rotordynamic performance of the honeycomb seal with swirl-reverse rings

Honeycomb seals are a crucial component to restrict the leakage flow and improve system stability for the turbomachines and aero-engines.In this work,the leakage and rotordynamic performance of honeycomb seals with the Swirl-Reverse Ring(SRR)is predicted by employing the approach of Computational Fluid Dynamics(CFD)and the multifrequency whirling model theory.Numerical results show that the positive preswirl flow and circumferential velocity can be effectively weakened for the honeycomb seal as SRR is introduced.The obtained results also suggest that the direct stiffness,direct damping,and effective stiffness will not reduce,for the honeycomb seal is introduced to SRR.However,the honeycomb seal with SRR can significantly reduce the crosscoupled stiffness and remarkably enhance the effective damping.Meanwhile,the absolute value of negative tangential force acting on the rotor surface significantly increased for the honeycomb seal introduced SRR.Therefore,the whirling velocity of the rotor would be weakened.This phenomenon would be conducive to improve the stability of the rotor.Besides,the performance of SRR can be further enhanced when SRR possesses a smaller bending angle,and a higher arrangement density and height.

Effect of hole arrangement patterns on the leakage and rotordynamic characteristics of the honeycomb seal

The honeycomb seal is a vital component to reduce the leakage flow and improvethe system stability for the turbomachines. In this work, a three-dimensional model is established for the interlaced hole honeycomb seal (IHHCS) and the non-interlaced hole honeycombseal (NIHHCS) to investigate its leakage and rotordynamic characteristics by adopting computational fluid dynamics (CFD). Results show that the hole arrangement patterns have littleimpact on the pressure drop and turbulence kinetic energy distribution for the seals, and theIHHCS possesses a slightly lower leakage flow rate than the NIHHCS. Moreover, the numericalresults also show that the NIHHCS possesses a better rotordynamic performance than theIHHCS at all investigated conditions. Both seals show a larger k and a lower Ceff with the increase of the positive preswirl ratios and rotational speeds, while the negative preswirl ratioswould reduce the k and improve the Ceff. The NIHHCS possesses a higher absolute value ofFt for all operating conditions, this could explain the distinction of Ceff for both seals atdifferent working conditions.