Dynamic Characteristics of Labyrinth Seal and Rotor Stability Considering Swirl Brakes

Abstract

The numerical solution model of the labyrinth seal considering the multiple frequencies elliptical whirling of the rotor and swirl brake was established by the computational fluid dynamics (CFD) technique. Then, the dynamic characteristics and response force characteristics of the labyrinth seal under the condition of a preswirl inlet were studied on the basis of experimental verification of the accuracy of the numerical solution method. The influence of the circumferential solidity of the swirl brake and the preswirl ratio on the flow field between the swirl brakes and the average circumferential velocity of seal cavities were analyzed. These results show that with the increasing rotor speed, the airflow circumferential velocity in the labyrinth seal chamber is increased, and the logarithmic decrement rate of the seal-rotor system is decreased, resulting in the rotor stability being decreased. With the increasing inlet/outlet pressure ratio, the airflow circumferential velocity of the labyrinth seal cavities is decreased, the logarithmic decrement rate of the seal-rotor system is increased, causing the rotor stability is increased. With the increasing circumferential solidity of the swirl brake, cross-coupled stiffness decreases, the direct damping and effective damping increase. It contributes to rotor whirling be inhibited, and rotor stability is increased. The rotor stability can be further improved with the increasing radial length of the swirl brake. The effective damping of the labyrinth seal with 40-extended swirl brakes increases by 33.7% compared to the labyrinth seal with no swirl brakes. With the increasing the preswirl ratio, the cross-coupled stiffness increases, the direct damping and effective damping decreases, and the phase angle of the response force is decreased. It arouses that the stability of the rotor is decreased. With the increasing of whirling frequency, the cross-coupling stiffness and direct damping increase, while the effective damping decreases first and then increases, resulting in the rotor stability being decreased first and then increased. The previous research provides a theoretical basis for the structure design of the swirl brake.