Numerical simulation of turbulence and transport of fine particulate impurities in street canyons

При помощи LES-модели, содержащей блок лагранжева переноса частиц, проведены расчеты турбулентности и распространения мелкодисперсных примесей в городской среде. Рассматривалась упрощенная геометрия периодической последовательности городских каньонов при поперечном направлении среднего ветра. Проведено тестирование различных лагранжевых методов и их сравнение с эйлеровыми методами переноса концентрации примесей, а также сравнение результатов расчетов с лабораторными данными. Выполнены расчеты переноса тяжелых углеродных частиц с размерами до семидесяти микрон в диаметре. На основе анализа лагранжевых траекторий частиц выявлены закономерности переноса мелкодисперсной примеси турбулентностью и крупными вихрями. The LES-model combined with the Lagrangian particle transport procedure is used to simulate the turbulence and propagation of particulate impurities in urban environment. A simplified geometry for a periodic sequence of urban canyons is considered in the case of the transverse mean wind direction. A number of the Lagrangian methods are tested and compared with the Eulerian methods of scalar concentration transport. The obtained numerical results are also compared with experimental data. The transport of heavy carbon particles up to seventy microns in diameter is numerically studied. The regularities in the impurity transport by the turbulence and large eddies are revealed on the basis of the analysis of Lagrangian particle trajectories.

Numerical Simulation of Contaminant Dispersion Within an Aircraft Interior

A hybrid numerical model has been developed to simulate contaminant dispersion within an aircraft interior. A two-equation Low-Reynolds-Number adaptive FEM model is used for simulating turbulent flow within an aircraft. Coupled with Lagrangian Particle Transport Technique, contaminant dispersion within aircraft interiors can be accurately simulated. Mesh independent studies can be avoided when using the adaptive technology, an L2 norm error estimator is used to guide the adaptation procedure. By using the adaptive algorithm, mesh independent studies can be avoided.

Simulation of Heat, Mass, and Momentum Transfer Within Building Interiors

An hp finite element-based model has been developed to calculate heat, mass, and momentum transfer within rooms and building interiors. The hp-adaptive methodology is based on both mesh enrichment (h-adaptation) and spectral order incensement (p-adaptation) in an effort to produce accurate results with the least computational cost. A Lagrangian Particle Transport (LPT) technique is coupled with the adaptive scheme to simulate mass transport. The model is particularly amenable for depicting the transport of contaminants associated with indoor air quality. The hp-adaptive algorithm is validated using natural convection in a square enclosure. The model is subsequently applied to the simulation of momentum, heat, and mass transport within building interiors: air and temperature distribution patterns are presented along with potential pathways of a powder dispersing within an office.

Evaluation of the Effect of Horizontal Diffusion on the Long-Range Atmospheric Transport Simulation with Chernobyl Data

The effect of horizontal diffusion on the long-range transport simulation is examined with a Lagrangian particle transport model. The transport of radioactivity released from Chernobyl is simulated by the model with different values of horizontal diffusivity. The computed concentrations are statistically compared with measured concentration. The best simulation is found when the magnitude of the horizontal diffusivity is between 3.3 × 104 and 1.0 × 105 m2 s−1. The performance of empirical formulas of horizontal diffusion, in which mean-square displacement σy is specified as a function of time, is also examined. A part of measured concentrations, which are relatively low concentrations, cannot be explained by transport and diffusion only. It is shown that these measured concentrations can be explained by resuspension of deposited radioactivity.