Large-eddy simulation of pollutant dispersion in a cavity at fine grid resolutions

This study validates large-eddy simulations (LESs) at fine grid resolutions to analyze the turbulent dispersion of pollutants in a cavity space, representing an urban street canyon. A pollution dispersion experiment was conducted using a physical model of a cavity with a height (H) of 1.0 m and an aspect ratio of unity (1:1). A line source at the bottom center of the cavity was used to deliver the tracer gas (a mixture of ethylene and synthetic air). The wind velocity was measured with a hot-wire anemometer. The tracer gas concentration was measured using a fast flame ionization detector. Following the physical experiment, LESs were conducted under the same model settings. Simple orthogonal grids were employed for the LESs with a grid spacing of H/200 and H/400. The LESs produced a good prediction of the mean and root-mean-square (RMS) velocity values. The LESs also predicted the mean, RMS, and percentiles of concentration well. However, a slight grid-dependency existed for the 95th and 99th concentration percentiles and the power spectral density of concentration at high-frequencies. The high percentiles were under predicted in the LESs as compared to the experiment near the source, especially in the coarser grid simulation.