A novel approach to reduce the computation time for CFD; hybrid LES–RANS modelling on parallel computers

摘要

Large Eddy Simulation is a method of obtaining high accuracy computationalresults for modelling fluid flow. Unfortunately it is computationally expensivelimiting it to users of large parallel machines. However, it may be that theuse of LES leads to an over-resolution of the problem because the bulk ofthe computational domain could be adequately modelled using the Reynoldsaveraged approach.A study has been undertaken to assess the feasibility, both in accuracy andcomputational efficiency of using a parallel computer to solve both LES andRANS type turbulence models on the same domain for the problem flow overa circular cylinder at Reynolds number 3 900To do this the domain has been created and then divided into two sub-domains,one for the LES model and one for the kappa - epsilon turbulence model. The hybridmodel has been developed specifically for a parallel computing environmentand the user is able to allocate modelling techniques to processors in a waywhich enables expansion of the model to any number of processors.Computational experimentation has shown that the combination of the Smagorinskymodel can be used to capture the vortex shedding from the cylinder andthe information successfully passed to the kappa - epsilon model for the dissipation of thevortices further downstream. The results have been compared to high accuracyLES results and with both kappa - epsilon and Smagorinsky LES computations on thesame domain. The hybrid models developed compare well with the Smagorinskymodel capturing the vortex shedding with the correct periodicity.Suggestions for future work have been made to develop this idea further, andto investigate the possibility of using the technology for the modelling of mixingand fast chemical reactions based on the more accurate prediction of theturbulence levels in the LES sub-domain.