A Numerical Study of Gas Dispersion over a Generic Frigate: RANS versus LES CFD Simulations

This paper presents some Computational Fluid Dynamics (CFD) simulation results of air flow and gas dispersion for a simple bluff body configuration and for a frigate with generic superstructure. The simple configuration is a cubic block with a top vent. The frigate has a superstructure consisting of different blocks and an exhaust stack. The simple configuration is studied to support the analysis of the simulation results for the more complex frigate model. The CFD simulations are performed with two different approaches: steady Reynolds-averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES). CFD validation is performed based on wind tunnel measurements for the simple configuration. It confirms that LES clearly performs better than steady RANS, mainly due to the more accurate reproduction of separation and recirculation zones and due to the reproduction of the inherent unsteadiness in the flow field. These basic RANS deficiencies explain the large differences in results between the RANS and LES results for the frigate. It is shown that the consequences of these deficiencies for the gas concentration field are amplified by the more complex geometry of the frigate model.