We present numerical simulations of solidification in a vertical cylindrical annulus with temporal evolution of three interfaces, i.e., solid-liquid, solid-gas, and liquid-gas, and with the presence of natural convection. The numerical technique used is an axisymmetric front-tracking/finite difference method in which the interface separating two phases is represented by connected elements moving on a stationary grid. The governing Navier-Stokes and energy equations are solved in the entire domain with the no-slip and isothermal boundary conditions treated by interpolation techniques. A simple tri-junction condition is included due to the presence of three phases. Effects of various dimensionless parameters such as the Prandtl number Pr, the Stefan number St, the Rayleigh number Ra, the Weber number We, the dimensionless initial temperature of the liquid theta(0), and the density ratio of the solid to liquid phases rho(sl) are investigated. The effect of the tri-junction in terms of the growth angle phi(gr) is also considered. Numerical results show that the shape of the solidified phase is strongly affected by rho(sl) and phi(gr). Volume expansion (rho(sl) < 1.0) produces a U-shaped top surface while shrinkage (rho(sl) > 1.0) forms a cavity near the outer wall of the annulus. An increase in phi(gr) results in an increase in its slope near the outer wall. Without volume change (rho(sl)=1.0), the top surface of the solidified phase becomes more curved with an increase in Pr or We. In contrast, varying St in the range of 0.01-1.0, Ra in the range of 10(3)-10(6) or theta(0) in the range of 1.0-2.0 has only a very minor effect on the top surface. Concerning the circulation flows induced by natural convection, the remarkable effects are yielded by variation of Ra and theta(0): increasing Ra or theta(0) results in an increase in the strength and the number of circulations. The circulations along with the interfacial tension force are the sources of the top front and solidification interface deformation. In addition, the effects of these parameters on the solidification rate are also investigated. (C) 2017 Elsevier Ltd. All rights reserved.