A Mesoscale-to-Microscale modeling capability using the Weather Research and Forecasting (WRF) model coupled to a special purpose, high-resolution Computational Fluid Dynamics (CFD) model is being made. These independent models are being integrated together via the Model Coupling Environmental Library (MCEL), which is a client/server, dataflow software model that provides sufficient data transfer and data filter capability in order to perform both upscale (CFD to WRF) and downscale (WRF to CFD) data transfer. Previous studies [Coirier, et al., 2006] have shown a quantifiably improved accuracy of urban area transport and dispersion modeling by the use of a file-based coupling to downscale data from WRF to a high-resolution CFD model. The work being undertaken here is intended to provide a more useful capability by coupling the models loosely in the MCEL environment, whereupon we may evaluate the potential improvements at both scales, as well as evaluate different techniques to perform the upscale and downscale data transfers.

In order to achieve this coupled capability, modifications to both WRF and the MCEL library are being made, and a new special-purpose CFD model is being developed to be run within this coupled environment. In this paper we outline the coupling approach using the MCEL library and describe the integration of WRF into this environment. The new, high-resolution urban CFD model being developed for this study is described in detail, and model validation study results using the new model are shown. This CFD model is designed to be run in a parallel computing environment using the PETSc parallel sparse matrix library, and solves the low-Mach number preconditioned, Reynolds-Averaged Navier-Stokes (RANS) equations using a low-Mach number preconditioned, Finite-Volume scheme. Details behind the numerics and overall approach are shown, including parallel scalability studies and model validation results. We show how we use downscaled data obtained from WRF through the MCEL filters which is applied as boundary conditions for the CFD model, which then cycles to a new, quasi-steady state, whereupon it performs an upscale data transfer through MCEL. Downscaled data corresponding to an Intensive Operating Period (IOP) of the Joint Urban 2003 (JU2003) field test conducted in Oklahoma City is used to demonstrate the new coupled models.

* Director/Defense Applications Branch. Corresponding Author: wjc@cfdrc.com, (256) 726-4927

CFD Research Corporation

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References

Coirier, W.J., Kim, S., Chen, F., Tuwari, M.,: 2006.b. Evaluation of urban scale contaminant transport and dispersion modeling using loosely coupled CFD and mesoscale models, American Meteorological Society, 6th Symposium on the Urban Environment.