Effect Of Oscillation On The Dynamics Of Bubbly Flow In Channel

Gas-liquid two-phase flow is a complex problem of multi-application and multi-discipline.As a common and important flow pattern of gas-liquid two-phase flow,bubbly flows involve a wide range of length scales and have a large number of deformable phase interfaces whose topological structure will change.Although many key problems need to be solved,the related research results will be of great engineering application value.Front-tracking method(FTM)is a very effective and mature method for numerical simulation of bubbly flows.For FTM,the phase interface represented by Lagrangian marker points achieves high-precision calculation of the geometric parameters of the interface.This method can maintain the existence of a sharp interface in the case of large deformation of the interface,and has good mass and energy conservation.The dynamics of bubbly flows in the oscillating flow field is studied using FTM.Specific research contents and main conclusions are as follows:Firstly,a numerical simulation model of the oscillating bubbly flows in shear flow field is established.In two-and three-dimensional flows,equal-sized and nearly circular bubbles are placed randomly in the flow field at the initial moment.The bubbles and the ambient liquid are driven by the imposed shear force and periodically varying pressure gradient.The results show that under the action of the periodically varying pressure gradient,the bubbles will be arranged in bubble columns in a direction perpendicular to the pressure gradient.However,strong enough shear force will break up the bubble columns and make the distribution of bubbles more uniform.The effect of shear force on the flow is different at low shear rate,moderate shear rate,and high shear rate regimes.In the low shear rate regime,the evolution of the average inclination angle of the bubble columns with the shear rate approximately satisfies a quadratic polynomial.The flow is also affected by the Reynolds and the Euler numbers.As these two numbers decrease,the low shear rate regime,within which stable tilted columns of bubbles are obtained,becomes smaller.Secondly,on the basis of the above research work,the change of bubble topology is considered,and a numerical simulation model of two-way oscillating bubbly flows is established.The influence of the amplitude and frequency of the periodically varying pressure gradients acting on the X-and Z-axes on the flow is systematically studied.For collision and coalescence of two tetradecane droplets,the simulation results of FTM are compared with the experimental results in literature,which verifies the validity and accuracy of the module dealing with the change of interface topology in the code.The results show that two-way oscillation will drive bubbles together,promoting coalescence.The flow varies with the amplitude and frequency,resulting in crawling flow,revolving flow,and oscillating flow.With the increase of the amplitude,the critical frequencies that divide these three flow patterns also increase.Corresponding to each amplitude,there is a frequency in the transition region of the crawling flow and the revolving flow that gives the fastest coalescence.Finally,the research contents are summarized,and the future work is prospected.