Interfacial stability in vertical swirling annular two-phase flow

The linear stability of liquid film flowing upward the inner surface of vertical cylinder under the action of the swirling gas core flow is investigated taking exactly the centrifugal force and curvature of the cylinder into account. Swirl has been considered by superposing a circular movement on the annular flow. The theoretical model of the stability of interface to small perturbation is established by analyzing the normal force balance condition at the wavy interface. The characteristic equation is solved and the stability criterion is obtained. The stability characteristics of neutral, growing and damped modes are presented showing the influences of swirl intensity, relative motion of gas-liquid flow, and the surface tension force. The modeling results indicate that the swirling of the gas phase stabilizes the film flow while the curvature of the cylinder destabilizes it. For strong swirling annular flow, it is found that there is a small influence of surface tension on the stability of interface because the stabilizing centrifugal force is dominant on this condition. The neutral wavelength is found to be very sensitive to the values of swirl intensity and cylinder radius when gas-liquid relative movement is small. However, when gas flow rate is large enough, there is no significant difference in its value.