Influence of operating parameters and cavity geometry on rotor dynamic characteristics of hole-pattern damping seal with dovetail-like diversion grooves

The operating parameters and cavity geometry significantly affect the sealing properties and rotor stability of the hole-pattern damping seal (HPDS). The three-dimensional numerical analysis model for the innovative dovetail-shaped hole-pattern damping seal (D-HPDS) was established. This model was used to study effects of inlet pressure, rotational speed, preswirl ratio, seal axial length, and cavity diameters on the rotor-dynamic characteristics of D-HPDS and circular-shaped HPDS (C-HPDS) using the dynamic mesh method and multi-frequency elliptic whirling model. Results show that under different conditions of cavity structures and operating parameters, the effective damping and stiffness of D-HPDS compared with C-HPDS improved to different degrees. The larger cavity diameter (d = 8 mm) and the longer axial length (S = 12) significantly enhanced the damping characteristics of D-HPDS, with the average effective damping increasing by up to 25. At rotational speeds of 0 to 7500 rpm and pressure ratios below 6.9, the negative vortex force (K_xy < 0) produced by low-speed double vortices in the HPDS cavity suppresses circumferential swirling flow caused by a high circumferential driving force at high speeds and a low axial driving force at low-pressure ratios. Therefore, D-HPDS reduces the sensitivity to speed and pressure ratio changes, improves the effective damping coefficient of the seal, and mitigates the instability issues of C-HPDS at low frequencies. Primarily, the inlet preswirl affects the flow field distribution at the inlet and has a minor impact on the dynamic characteristics of D-HPDS.