The influence of latent heat and natural convection upon the melt-crystal interface in a vertical Bridgman-Stockbarger crystal growth system is studied by numerical simulation. The temperature and velocity field are computed using an average technique which consists of representing the solid-liquid mixture as a single continuum medium. The physical properties of the equivalent medium are evaluated from average values which characterize each phase present in the system. The numerical resolution is performed using a finite volume method including a high-order upwind scheme and PISO algorithm for the pressure-velocity coupling. The numerical results show the effects of latent heat and gravity magnitude upon the flow pattern in the melt. The consequences upon the melt-crystal interface are also analyzed.