In this work, numerical simulations are carried out to characterize the impact of obstacles on flame propagation velocity to properly assess the consequences of Unconfined Vapor Cloud Explosions (UVCE).Within this scope, an UVCE within a congested environment is simulated using RANS modeling of the turbulence. Combustion phenomena are characterized through the progress variable transport equation. The simulation is done with the open source library OpenFoam. Numerical results are compared with data from the INERIS and GDF-SUEZ experimental campaign EXJET (hydrogen-air and methane-air explosions).