H14-168 ATMOSPHERIC WIND FIELD SIMULATIONS OVER COMPLEX TERRAIN USING PARTIALLY CONVERGED CFD CALCULATIONS - APPLICATION TO MODELLING OF ATMOSPHERIC DISPERSION FOR OPERATIONAL PURPOSES

In modeling atmospheric dispersion over complex terrain (relief, roughness or heat flux change), Computational Fluid Dynamics (CFD) codes can be a powerful tool for simulating air flow with very high spatial resolution. However, the well-known drawback of the CFD approach is that it is time consuming. In this paper, a method which uses partially converged CFD solutions as a way of reducing CPU time, while keeping the precision of the solution at an acceptable level, is presented. We therefore demonstrate that it is possible to reach a wind field solution very close to the converged solution, in a small fraction of the CPU time needed to reach the fully converged solution. We present an optimum point of convergence,depending on the complexity of the terrain, for several cases of simulations with the commercial CFD code Fluent. Such complexities include steepness of hills and valleys, roughness of terrain and thermal stratification. We present an estimate of the error in comparison to the fully converged solution and evaluate the gain of CPU time following each case study.Finally, we strengthen our conclusions by a comparison with wind tunnel experiments in the presence of hills.