Rotordynamic Analysis of Textured Annular Seals With Multiphase (Bubbly) Flow

Abstract

For some applications it must be considered that the flow in the annular seal contains a mixture of liquid and gas. The multiphase character of the flow is described by the volume fraction of gas (usually air) contained in the liquid under the form of bubbles. The fluid is then a homogenous mixture of air and liquid all thru the annular seal. Its local gas volume fraction depends on the pressure field and is calculated by using a simplified form of the Rayleigh-Plesset equation. The influence of such of a multiphase (bubbly) flow on the dynamic characteristics of a straight annular seal is minimal because the volume of the fluid is reduced. The situation is quite different for textured annular (damper) seals provided with equally spaced deep cavities intended to increase the damping capabilities and to reduce the leakage flow rate. As a by-product, the volume of the fluid in the seal increases drastically and the compressibility effects stemming from the bubbly nature of the flow are largely increased even for a low gas volume fraction. The present work depicts the influence of the gas volume fraction on the dynamic characteristics of a textured annular seal. It is shown that variations of the gas volume fraction between 1% and 0.1% can lead to frequency dependent stiffness, damping and added mass coefficients.