We develop a fully 2D incompressible flow model for the AlN physical vapor transport (PVT) growth process by the Finite Element Method. In this model, the effects of multiphase vapor diffusion, buoyancy, and the Stefan flow are taken into account. We also investigate the influences of the crucible shape on the mass transport in a 2-in. AlN growth chamber with numerical experiments. The simulation results show that the uniformity of the initial growth rate on the deposition surface is strongly dependent on the crucible shape, and it could be improved by increasing the crucible sidewall expansion angle. The optimal expansion angle is found to be between 15 degrees and 18 degrees in order to obtain a slight convex growth interface under our specified growth conditions. The improvement of the initial growth interface uniformity is mainly due to the local Al gas pressure gradient near the deposition surface. The simulation results also reveal that a transport limitation of Al atoms at the deposition surface could be the most likely rate-limiting step for AlN PVT growth.