Evaluation of notional nozzle approaches for CFD simulations of free-shear under-expanded hydrogen jets

Several approaches are usually applied for modelling the source of high pressure under-expanded jets, ranging from the computationally expensive resolution of the jetʹs 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 H2 round jets. The experimental data covered horizontal H2 releases issuing from small nozzles (0.25–1 mm diameter). Three two-equation turbulence models were chosen for the simulations, the popular standard k-ε, the Shear Stress Transport (SST) and the baseline (BSL) k-ω 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.