Taylor bubble dynamics in pipe fittings: A numerical study

Abstract

Present study is a numerical effort towards capturing the evolving and topologically complex interfacial behavior of a Taylor Bubble while it is passing through an orifice like constriction in a vertical tube. These simulations are performed using the adaptive, incompressible quad tree based 2D axis-symmetric Gerris solver (Popinet, J Comput Phys 228(16):5838–5866, 2009 [1]) which is based on classical geometrical VOF scheme that proceeds in two steps i.e. reconstruction of the interface and advection of the same followed by computation of mass flux. The crucial involvement of interfacial surface tension in controlling the hydrodynamics of the phenomena is taken care of by making necessary modifications to the momentum equation based on the continuum surface force (CSF) concept coined by Brackbill et al. (J Comput Phys 100(2) 335–354, 1992 [2]). After volume fraction calculation, the interface reconstruction is achieved using a second order accurate height-function (HF) method which ensures an improved extent of volume flux conservation for the VOF scheme. Initially the axis-symmetric code has been developed for the uprise of both spherical as well as Taylor Bubble in a straight vertical channel and then the obtained results have been validated against the available velocity correlations for respective cases. After the validation we moved on to incorporate the effect of constriction in the passage on interface dynamics. Simulations have been carried out for a wide variation of constriction ratio as well as fluid properties to capture the dependence on each critical parameter properly. Observed trends came to be satisfactory as per the expectations.