Jean-François Vinuesa

Revisiting the Local Scaling Hypothesis in Stably Stratified Atmospheric Boundary-Layer Turbulence: an Integration of Field and Laboratory Measurements with Large-Eddy Simulations

The ‘local scaling’ hypothesis, first introduced by Nieuwstadt two decades ago, describes the turbulence structure of the stable boundary layer in a very succinct way and is an integral part of numerous local closure-based numerical weather prediction models. However, the validity of this hypothesis under very stable conditions is a subject of ongoing debate. Here, we attempt to address this controversial issue by performing extensive analyses of turbulence data from several field campaigns, wind-tunnel experiments and large-eddy simulations. A wide range of stabilities, diverse field conditions and a comprehensive set of turbulence statistics make this study distinct

Dynamic LES Modeling of a Diurnal Cycle

Abstract The diurnally varying atmospheric boundary layer observed during the Wangara (Australia) case study is simulated using the recently proposed locally averaged scale-dependent dynamic subgrid-scale (SGS) model. This tuning-free SGS model enables one to dynamically compute the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. It is shown that this SGS-model-based large-eddy simulation (LES) has the ability to faithfully reproduce the characteristics of observed atmospheric boundary layers even with relatively coarse resolutions. In particular, the development, magnitude, and location of an observed nocturnal low-level jet are depicted quite well. Some well-established empirical formulations (e.g., mixed layer scaling, spectral scaling) are recovered with good accuracy by this SGS parameterization. The application of this new-generation dynamic SGS modeling approach is also briefly delineated to address several pr...

A dynamic similarity subgrid model for chemical transformations in large-eddy simulation of the atmospheric boundary layer

In large-eddy simulations (LESs) of atmospheric reacting flows, homogeneous and instantaneous mixing of reactants within a grid-cell is usually assumed. However, highly reactive species are often segregated or pre-mixed at small scales. In this paper, we propose a parameterization to account for the effect of the unresolved scales on the chemical transformations. Its formulation relies on the description of the subgrid unresolved reactant covariance as a function of the resolved covariance by using scale-similarity arguments. A dynamic procedure is used to compute the model coefficient from the resolved reactant concentration fields, therefore not requiring any parameter specification or tuning. In simulations of a convective boundary layer with a fast second-order reaction, using the new model is found to perform better than ignoring subgrid chemistry effects.

Dynamic models for the subgrid-scale mixing of reactants in atmospheric turbulent reacting flows

The effects of the subgrid scales on chemical transformations in large-eddy simulations of the convective atmospheric boundary layer (CBL) are investigated. Dynamic similarity subgrid-scale models are formulated and used to calculate the subgrid-scale covariance. The dynamic procedure allows for simulations free of parameter tuning since the model coefficients are computed based on the resolved reactant concentrations. A scale-dependent procedure is proposed that allows relaxing the assumption of scale invariance used in the dynamic similarity model. Simulation results show that both models are able to account in part for the effect of the segregation of the scalars at the subgrid scales, considerably reducing the resolution dependence of the results found when no subgrid covariance model is used. The scale-dependent dynamic version yields better results than its scale-invariant counterpart.

Relating Small-Scale Emission and Concentration Variability in Air Quality Models

A novel approach to account for the spatial variability of the small-scale emission in air quality models is proposed. This approach includes a formulation for the sub-grid variability of pollutant concentrations and relates it to the spatial het- erogeneity of the emissions. The parameterization is implemented in a 3D transport model and tested against large eddy simulations of convective atmospheric bound- ary layers.