The prediction of orientation for high aspect ratio particle composites such as nanocomposites or fiber composites is required in order to optimize the mold design of injection molding composites. At present, commercial simulators for fiber composites ignore the viscoelastic behavior of the polymeric matrix and perform the simulations in a decoupled scheme using Hele-Shaw flow approximations. Therefore the predictions of these simulations were highly limited. In this study, the flow through a center gated disk and end-gated plaque geometry is simulated numerically for a highly concentrated short glass fiber in a PBT (Newtonian) or PP (viscoelastic) matrix. The particles are modeled considering Brownian motion for nanoparticles, and the rotary diffusion term and non-affine motion for fibers. The viscoelastic matrix is modeled using a Phan Thien-Tanner model. For this, a 2D Finite Element Method analysis was performed using the traditional Galerkin method for the balance equations and discontinuous Galerkin for the constitutive equations. The impact of the frontal flow region, initial fiber orientation and viscoelasticity matrix was investigated. The predictions were evaluated with experimental data obtained using laser confocal microscopy and optical reflection microscopy.