Several approaches are usually applied for modelling the source of high pressure under-expanded jets, ranging from the computationally expensive resolution of the jet's shock structure to simple formulae (pseudo-source or notional nozzle approaches). However, the assumptions made in each approach introduce inaccuracies in the CFD calculations. The objective of this work was twofold; to compare and evaluate the performance of both selected notional nozzle approaches and turbulence models with experimental results of free-shear high momentum H-2 round jets. The experimental data covered horizontal H-2 releases issuing from small nozzles (0.25-1 mm diameter). Three two-equation turbulence models were chosen for the simulations, the popular standard k-epsilon, the Shear Stress Transport (SST) and the baseline (BSL) k-omega model together with five notional nozzle approaches. The numerical results were presented in a systematic way in order to make general conclusions on the performance of both the approaches and models. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.