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This study describes the numerical implementation, verification and validation of an immersed boundary method (IBM) in the atmospheric solver Meso-NH for applications to urban flow modeling. The IBM represents the fluid–solid interface by means of a level-set function and models the obstacles as part of the resolved scales. The IBM is implemented by means of a three-step procedure: first, an explicit-in-time forcing is developed based on a novel ghost-cell technique that uses multiple image points instead of the classical single mirror point. The second step consists of an implicit step projection whereby the right-hand side of the Poisson equation is modified by means of a cut-cell technique to satisfy the incompressibility constraint. The condition of non-permeability is achieved at the embedded fluid–solid interface by an iterative procedure applied on the modified Poisson equation. In the final step, the turbulent fluxes and the wall model used for large-eddy simulations (LESs) are corrected, and a wall model is proposed to ensure consistency of the subgrid scales with the IBM treatment. In the second of part of the paper, the IBM is verified and validated for several analytical and benchmark test cases of flows around single bluff bodies with an increasing level of complexity. The analysis showed that the Meso-NH model (MNH) with IBM reproduces the expected physical features of the flow, which are also found in the atmosphere at much larger scales. Finally, the IBM is validated in the LES mode against the Mock Urban Setting Test (MUST) field experiment, which is characterized by strong roughness caused by the presence of a set of obstacles placed in the atmospheric boundary layer in nearly neutral stability conditions. The Meso-NH IBM–LES reproduces with reasonable accuracy both the mean flow and turbulent fluctuations observed in this idealized urban environment. [ABSTRACT FROM AUTHOR]

This paper focuses on a decisive step toward large-eddy simulation of a solid-rocket motor jet. A model based on solving constant-pressure reactors with a chemical solver was implemented. It is able to evaluate the temperature and chemical species distributions resulting from afterburning chemistry along streamlines of an existing frozen flowfield. This method was applied to a time-averaged flowfield obtained from large-eddy simulations of a single-species solid-rocket motor jet. Despite its limitations, the model is accurate enough to observe the various steps of the chemical mechanism and assess the effect of uncertainties of the rate parameters on chlorine reactions. The results are coherent with those obtained in previous studies and offer a relevant evaluation of the flowfield characteristics, helpful for future large-eddy simulations of a multispecies, reactive solid-rocket motor jet. [ABSTRACT FROM AUTHOR]

This paper presents the results of large-eddy simulations of a solid rocket booster jet. An inert gas thermodynamically equivalent to the rocket exhaust is injected through the entire nozzle of the booster in the atmosphere at flight conditions of 20 km of altitude. A local time-stepping method via coupling multi-instances of a fluid solver is used to extend the computational domain up to 400 nozzle exit diameters. The mean flow and the turbulence statistics of the resulting supersonic coflowing jet are analyzed. The structure of the flow is identified, and important features show good agreement with other studies. In particular, the potential core length is consistent with previous analysis, whereas in the far field, the decay rate of axial velocity and the jet spreading rate are consistent with those of incompressible coflowing jets. Reynolds stresses profiles and turbulence scales, evaluated via two-point velocity correlations, are coherent with available data from high-speed jets. This study proves that the methodology applied for this single-species jet is efficient and reliable. Therefore, it can be directly used for large-eddy simulations of a booster jet that model the complex chemistry occurring in the plume. [ABSTRACT FROM AUTHOR]