Stability effect of the lateral lift force in bubbly flows


Stability effect of the lateral lift force in bubbly flows

Lucas, D.; Krepper, E.; Prasser, H.-M.; Manera, A.

The role of the lift force for the stability of bubbly flows is discussed. The main interest is directed towards bubble columns, since instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous flow regimes. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Such gradients may result from the main liquid flow or from local disturbances in case of initially homogeneous flows. Depending on the sign of the lift force such local disturbances in a homogeneous flow may be damped or enhanced. The corresponding feedback mechanism was previously analysed by means of a linear stability analyses. In the result criteria for stability were obtained for mono-dispersed flow, for a flow with two bubble size groups and finally with some additional approximations also for the case of N bubble size groups or a given bubble size distribution. Recently two different groups confirmed the stability criteria experimentally. Now the effects were investigated also by means of CFD simulations. In a first step bubble coalescence was excluded, while the second step comprises a numerical study which includes coalescence. In the latter case coalescence leads to a transition from stable to instable flow patterns along the height position in the column. The transitions fit well together with the criteria for stability. Finally the influence of the lift force is discussed also for other flow situations.

Keywords: bubbly flow; stability; bubble column; lift force

  • Contribution to proceedings
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany
    paper S1_Mon_C_9
  • Lecture (Conference)
    International Conference on Multiphase Flow - ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-10044
Publ.-Id: 10044