流體旋轉機械中，當流體經過軸封時，轉軸兩側流場壓降不同，產生一徑向作用力將轉子推回軸封中心位置，後人稱此現象為 Lomakin 效應。軸封之動態特性是會影響轉子系統的穩定性，提高系統的穩定性是轉子動力學分析上非常重要的問題。過去研究 Lomakin 效應對於動態係數影響的分析上，均著重在主勁度係數的影響，且影響 Lomakin 效應的各個因素也沒有完整的討論。本文特別針對流體因素作一系列討論，影響 Lomakin 效應的流體因素可以歸納為下列幾點：入口壓力流失係數，入口渦流效應，流體特性，如黏滯性、種類。並利用 CFD 軟體Fluent針對軸封建模、分析，來探討 Lomakin效應對於軸封的影響。主要結果有：入口壓力流失係數的增加不僅對 Lomakin 效應會有減弱的趨勢，促使系統穩定的主勁度係數以及主阻尼係數也都有降低的走向。入口渦流效應使 Lomakin 效應變差。入口渦流係數越大，主勁度係數以及主阻尼係數越小，而耦合勁度係數及耦合阻尼係數則越大，系統會趨向於不穩定狀態。

In turbo-machinery, dynamics of rotors is affected by Lomakin effects which are the radially restoring forces caused by the difference of the pressure drops between the opposite sides of the rotor when the fluid flows through seals. The dynamic characteristics of seals can affect the stability of the rotor systems.Rotor Stability is always an important research issue in rotordynamics. In previous research, the influence of Lomakin effects on the dynamics coefficients of seals were not investigated inclusively. Fluid factors that affect Lomakin effects are specially studied in this paper. The fluid factors on Lomakin effects include inlet loss coefficients, inlet preswirl, and fluid properties, such as viscosity and variety. Lomakin effects and dynamic characteristics of the plain seals were modeled and analyzed by Fluent, a CFD software. The results show the increase of inlet loss coefficients weakens the Lomakin effects, and decreases the direct stiffness and damping coefficients of seals, which deteriorates the stability of the rotor systems. Increase of inlet preswirl has the similar influence of reducing the direct coefficients, raising the coupled coefficients, and
destabilizing the rotor systems.