Effects of pressure ratio, rotational speed and inlet preswirl on the leakage and rotordy namic characteristics of a eight-bladed fully partitioned pocket damper seal (FPDS) were numerically investigated using proposed three-dimensional (3D) transient computa tional fluid dynamics (CFD) methods based on the multifrequency elliptical whirling orbit model. The accuracy and availability of the multifrequency elliptical whirling orbit model and the transient CFD numerical methods were demonstrated with the experimen tal data of frequency-dependent rotordynamic coefficients of the FPDS at two rotational speeds with high preswirl conditions. The frequency-dependent rotordynamic coefficients of the FPDS at three pressure ratios (three inlet pressures and three outlet pressures), three rotational speeds, three inlet preswirls were computed. The numerical results show that changes in outlet pressure have only weak effects on most rotordynamic coefficients. The direct damping and effective damping slightly increase in magnitude with decreasing outlet pressure at the frequency range of 20-200 Hz. The effect of inlet pressure is most prominent, and increasing inlet pressure for the FPDS results in a significant increase in the magnitudes of all rotordynamic coefficients. The magnitudes of the seal response force and effective damping are proportional to pressure drop through the seal. Increas ing rotational speed and increasing inlet preswirl velocity both result in a significant decrease in the effective damping term due to the obvious increase in the magnitude of the destabilizing cross-coupling stiffness with increasing rotational speed or increasing preswirl velocity. The crossover frequency of effective damping significantly increases and the peak magnitude of effective damping decreases with increasing rotational speed or increasing preswirl velocity. The destabilizing cross-coupling stiffness is mainly caused by the circumferential swirl velocity generating from high rotational speed and inlet preswirl. Reducing swirl velocity (such as swirl brake) can greatly enhance the sta bilizing capacity of the FPDS.In tro d u c tio n Annular gas seals are widely used in compressors, turbines and pumps as shaft, balance drums, interstage, and impeller eye seals to restrict leakage flow through rotor-stator clearances from high pressure regions to low pressure regions [1], Although the primary function of annular gas seals is to prevent leakage, which directly affects the aerodynamic efficiency and performance of turboma chinery, annular gas seals exhibit forces coefficients being gener ated from fluid-structure interaction forces between the rotor and seal stator components [2], These seal force coefficients can stabi lize or destabilize the rotor-bearing system and influence the vibration response of turbomachinery, hence, must be controlled to ensure that the rotor system of turbomachinery remains stable 'Corresponding author. Contributed by the Structures and Dynamics Committee of ASME for publication in the Journal of E ng...
