Computational and experimental investigation of a swirl nozzle for viscous fluids

•Comparison of experimental and numerical findings for a large-scale swirl nozzle.•Low Reynolds number flow conditions relevant for high-viscosity, bio-mass based fuels.•Inner-nozzle velocity field, discharge coefficient and spray angles are quantified.•Transient characteristics of the developing air core are investigated.•Predictive character of the simulation method for analyses of swirl nozzles is demonstrated.