液體平軸封之Lomakin效應與動態係數研究－流體因素分析

Lomakin Effects and Dynamic Coefficients of Liquid Plain Seals Influenced by Fluid Factors

楊大中(Ta-Chung Yang) ； 許家瑋(Chia-Wei Hsu)

《先進工程學刊》 5卷4期 (2010/10) Pp. 279-287

https://doi.org/10.29948/JAE.201010.0001

摘要

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。

關鍵字

軸封 ； Lomakin效應 ； 入口壓力流失係數 ； 入口渦流 ； 動態係數

並列摘要

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.

並列關鍵字

seal ； Lomakin effect ； inlet loss coefficient ； inlet preswirl ； dynamic coefficient