The investigation of rotordynamic characteristics and flow mechanisms in double-wall-hole honeycomb seal

In this paper, the influence of wall holes on the rotordynamic characteristics of the double-wall-hole honeycomb seal (D-WHHCS) is investigated and compared with that of the traditional honeycomb seal (HCS). A series of calculations are conducted under different working conditions using the computational fluid dynamics (CFD) method. An improved multi-frequency motion transient model is proposed, which reduces the average computational time by 37.4% with satisfactory accuracy maintained. The internal flow mechanisms of two seals are analyzed in detail. The results show that the D-WHHCS exhibits higher effective stiffness and lower effective damping than HCS's. The existence of wall holes effectively inhibits the circumferential flow in sealing gap, and generates asymmetric vortex structures in the cavities with axial numbered (N_hc) 14. The inhibition effect produces concentrated velocity regions in the sealing gap, which causes an energy-level-transition-like motion when fluid traveling from one disinhibited orbit to another in circumferential direction. That means circumferential motion needs more energy to increase its velocity, instead of being continuously accelerated. These phenomena lead to a higher direct stiffness in the D-WHHCS, while the reduction of circumferential shear and viscous dissipation results in lower direct and cross-coupled damping compared with HCS. Inlet preswirl has little effect on leakage performance but significantly influences rotordynamic coefficients of both seals by changing the circumferential flow in sealing gap. Negative inlet preswirl enhances effective stiffness and damping, thereby improving the static and dynamic stability of rotor system, whereas positive preswirl may introduce a crossover frequency and reduce stability margins.