Application of RANS and LES Based CFD to Predict the Short and Long Term Distribution and Mixing of Hydrogen in a Large Enclosure

Abstract

The paper presents CFD simulations from Reynolds Average Navier Stokes (RANS) and Large Eddy Simulation (LES) based approach of hydrogen release and dispersion inside the large enclosure and comparison with experimental data. The experiment was reported by HySafe Network of Excellence partners, consisting of a 1 g/s vertical hydrogen release for 240 s from an orifice of 20 mm diameter into a rectangular room of dimensions 7.2X2.88X3.78 m in length, height and width respectively. Two small openings were provided at the front and bottom side of the room. During the test hydrogen concentration time histories were measured at few positions in the room, for a period up to 5160 s after the end of release, covering both the release and the subsequent diffusion phases The CFD simulations were performed using a) a 3D transient in-house developed RANS CFD code b) LES based Fire Dynamics Simulator (FDS). Initially when the jet is injected the turbulence intensity is high, but later on the problem is diffusion dominated. Therefore suitable approaches were used to simulate the problem. Initially k-? High Re number model with standard wall function and buoyancy modification was used and subsequently the transport was modelled as laminar in RANS based approach. The default LES based scheme adopted for LES based computations. The gas mixture was treated as weakly compressible and gravity force was also considered. The results obtained by computations have a good agreement with experiment particularly for LES based calculation. The performed simulation provides useful insight regarding performance of CFD code to simulate hydrogen transport problem and this capability can be further utilized to simulate the hydrogen transport in the real containment geometries.