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Computation of gas dispersal in urban places or hilly grounds requires alarge amount of computer time when addressed with conventional multidimensionalmodels. Those are usually based on two-phase flow or Navier-Stokes equations.Different classes of simplified models exist. Among them, two-layer shallowwater models are interesting to address large-scale dispersion. Indeed,compared to conventional multidimensional approaches, 2D simulations arecarried out to mimic 3D effects. The computational gain in CPU time isconsequently expected to be tremendous. However, such models involve at leastthree fundamental difficulties. The first one is related to the lack ofhyperbolicity of most existing formulations, yielding serious consequencesregarding wave propagation. The second is related to the non-conservative termsin the momentum equations. Those terms account for interactions between fluidlayers. Recently, these two difficulties have been addressed in Chiapolino andSaurel (2018) and an unconditional hyperbolic model has been proposed alongwith a Harten-Lax-van Leer (HLL) type Riemann solver dealing with thenon-conservative terms. In the same reference, numerical experiments showedrobustness and accuracy of the formulation. In the present paper, a thirddifficulty is addressed. It consists of the determination of appropriate drageffect formulation. Such effects also account for interactions between fluidlayers and become of particular importance when dealing with heavy-gasdispersion. With this aim, the model is compared to laboratory experiments inthe context of heavy gas dispersal in quiescent air. It is shown that the modelaccurately reproduces experimental results thanks to an appropriate drag forcecorrelation. This function expresses drag effects between the heavy and lightgas layers. It is determined thanks to various experimental configurations ofdam-break test problems.

Modeling Heavy-Gas Dispersion in Air with Two-Layer Shallow Water Equations