A Simple Model for Two-Phase Slug Flow Induced Damping
NURETH-14 - 2011 September 25-30

Presented at:
2011 September 25-30
Toronto, Canada
Session Title:
A7-1 Mini Symposium on Flow-induced Vibration in Nuclear Components

Njuki Mureithi (Ecole Polytechnique)
Teguewinde Sawadogo (Ecole Polytechnique)
Fabien Bernard (ENSEEIHT)


The two-phase flows are prevalent in various industrial fields such as nuclear engineering, chemical engineering and the petroleum industry. At high speeds, flows through piping may generate significant excitation forces, particularly at joints and bends in piping systems.  Interestingly, the flows may also generate significant damping forces which can be desirable from a vibration damping point of view.

The question of exactly how internal two-phase flows generate damping remains largely unanswered. Indeed so is the question for external two-phase flows, which are even more complex. The problem addressed in this study is related to the behavior of tubular structures subjected to internal two-phase slug flow or nearly slug flow. The observation of slug flow subjected to transverse vibration led to consideration of the effects of sloshing liquid slugs due to the external vibration. Indeed, in flow visualization tests, the upper free surface of the slugs in vertical flow was found to deform significantly as the tube vibrated. This suggested a possible mechanism for energy transfer from the structure to the fluid which could be (at least partially) responsible for the observed two-phase flow-induced damping 

An analytical model is developed aimed at incorporating the most basic sloshing effects of liquid slugs travelling through a tube at low speed. The first part of the work demonstrates that considering slugs as as simple points masses travelling through the tube leads only to low energy transfer from the tube to the flow and thus cannot explain the level of energy transfer observed in experimental damping tests.

In the second part of the work, the flow dynamics within the slug are modeled to account for linear order free surface oscillations related to first mode sloshing. Numerical solution of the resulting equations shows that the energy transfer is much higher and results in damping levels of the same order as found in experimental measurements. The results suggest that sloshing of the individual slugs is an important mechanism of energy transfer for slug flow.

The analytical results are in qualitative agreement with experimental measurements. In view of the simplicity of the model, the results are encouraging. The model can, however, be improved to better represent more details of the flow.

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