Gas turbine performance is strongly dependent on the flow field inside the combustor. In the primary zone, the recirculation of hot products stabilises the flame and completes the fuel oxidation. In the dilution zone, the mixing process allows to obtain the suitable temperature profile at turbine inlet. This paper presents an experimental and computational analysis of both the isothermal and the reactive flow field inside a gas turbine combustor designed to be fed with natural gas and hydrogen. The study aims at evaluating the capability of a coarse grid CFD model, already validated in previous reactive calculations, in predicting the flow field and NOx emissions. An experimental campaign was performed on an isothermal flow test rig to investigate the combustion air splitting and the penetration of both primary and dilution air jets. These experimental data are used to validate the isothermal computations. The impact of combustion on the calculated flow field and on air splitting is investigated as well. Finally, NOx emission trend estimated by a post-processing technique is presented. The numerical NOx concentrations at the combustor discharge are compared with experimental measurements acquired during operation with different fuel burnt (natural gas or hydrogen) and different amount of steam injected. (C) 2011 Elsevier Ltd. All rights reserved.