In the present work, CFD simulations of a large scale open deflagration experiment are performed. Stoichiometric hydrogen-air mixture occupies a 20 m hemisphere. Two combustion models are compared and evaluated against the experiment: the Eddy Dissipation Concept model and a multi-physics combustion model which calculates turbulent burning velocity based on Yakhot's equation. Sensitivity analysis on the value of fractal dimension of the latter model is performed. A semi-empirical relation which estimates the fractal dimension is also tested. The effect of the turbulence model on the results is examined. LES approach and k-epsilon models are used. The multi-physics combustion model with constant fractal dimension value equal to 2.3, using the RNG LES turbulence model achieves the best agreement with the experiment. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.