*Article* **Transient CFD Simulation on Dynamic Characteristics of Annular Seal under Large Eccentricities and Disturbances**

**Kai Zhang 1, Xinkuo Jiang 2, Shiyang Li 1, Bin Huang 3, Shuai Yang 1, Peng Wu 1,\* and Dazhuan Wu 1,4**


Received: 17 June 2020; Accepted: 3 August 2020; Published: 5 August 2020

**Abstract:** Annular seals of turbomachinery usually suffer from various degrees of eccentricities and disturbances due to the rotor–stator misalignment and radial loads, while the discussion of annular seal under both large static eccentricities and dynamic disturbances is relatively limited. In this paper, the applicability of linear assumption and reliability of nonlinear dynamic model for eccentric annular seals under large eccentricities and disturbances is discussed based on the investigation of seals with various rotor motions through computational fluid dynamics (CFD). After the validation of transient CFD methods by comparison with experimental and bulk theory results, the dynamic behaviors of annular seal are analyzed by adopting both direct transient simulations and the nonlinear Muszynska model. The results show that the nonlinear dynamic model based on rotor circular whirls around seal center can predict the fluid excitations of different types of rotor motions well under small static eccentricities, while it is limited severely with large static eccentricities, which indicates that the dynamic characteristics of annular seal under large eccentricities are related with the rotor's motion ways. The paper provides a reference for studies of rotor–seal system with complex rotor motions considering radial loads or running across the resonance region.

**Keywords:** annular seal; CFD; dynamic coefficients; fluid forces; nonlinear dynamic model; static eccentricity
