Numerical experiments using MesoNH/ForeFire coupled atmospheric-fire model

In this study we attempt to couple the MesoNH atmospheric model in its large eddy simulation configuration with a fire contour model, ForeFire. Coupling is performed at each atmospheric time step, with the fire propagation model inputting the wind fields and outputting heat and vapor fluxes to the atmospheric model.

Typical resolution for the atmospheric model is 30 meters, such as the fire front represents a significant portion of the atmospheric surface mesh. The ForeFire model is a Lagrangian front tracking model that runs at a typical front resolution of 1 meter. If the approach is similar to other successful attempts of fire-atmosphere coupled models, the use of MesoNH and ForeFire implied the development of an original coupling method. Fluxes outputted to the atmospheric models are integrated using polygon clipping method between the fire front position and the atmospheric mesh. Another originality of the approach is the fire rate of spread model that integrates wind effect by calculating the flame tilt. This reduced physical model is based on the radiating panel hypothesis.

A set of idealized simulation cases has been performed to study the behavior of the coupled model, including a simple hill, different slopes, a canyon, as well as different fire front configurations. Preliminary results show that the coupled model is able to reproduce results that are comparable to other existing numerical experiments with a relatively small computational cost (one hour for a typical idealized case on a 200 GFlops capable computer).

MesoNH serves as a research model for the meteorological systems in France and Europe, and is well integrated within the operational tool chain. Future validation scenarios will be performed on nested simulations of real large wildfires.