In this study, a simplex nozzle is tested with water for the benchmarking of different flow simulation models. A large scale Plexi-glass transparent nozzle is used to reduce the influence of production tolerances on the performance. Experiments are conducted at different flow rates and CD, spray angle and film thickness parameters are evaluated. 2D and 3D hybrid RANS-LES multiphase flow simulations of simplex nozzle are validated against the experimental data. Multiphase nature of the flow is modelled by volume of fluid method. The main goal is to assess the capabilities and drawbacks of 2D axisymmetric and full sector 3D modeling approaches. It is observed that although full sector 3D simulations require HPC cluster systems, accuracies in validation parameters are quite satisfying. Conversely, 2D axisymmetric simulations which can be run on a single core and give a general outlook of the flow field, they show an overshoot of CD and film thickness over the selected range of flow rate. It is shown that this overshoot is mostly related with the inlet boundary condition, which can not take the flow contraction and/or separation at the inlet slots into account. After correcting the inlet velocity 2D simulations by using the 3D results, it is shown that the predictions can be quite close to the experimental data.