Predicting below-surface horizontal pore gas velocity in porous media from above-surface wind conditions and medium gas permeability

摘要

Below-surface horizontal pore gas velocity profiles in response to above-surface wind conditions were measured for 16 combinations of wind speed (1.4-5.7 ms(-1)) and wind gust frequency (0-1 Hz) in four porous media with different particle size (0.6-10 mm), yielding 64 combinations of wind condition and porous medium using a recently developed experimental gas tracer tracking method. Experiments were carried out under controlled conditions in a wind tunnel. Gusty wind conditions were created using a wind-driven propeller operating at variable rotation frequencies. A recently presented empirical model for predicting horizontal pore gas velocity in porous media in response to above-surface wind conditions was validated against the experimental data. The model uses one empirical parameter (B) together with the wind speed at the surface as input parameters. Further analyses were carried out to identify relations betweenB, above-surface wind conditions and porous medium properties. Results indicate that it is possible to accurately estimateBand thus predict below-surface pore gas velocity profiles based on porous medium properties and surface wind speed.Bwas found inversely proportional to above-surface wind speed, porous medium particle diameter and porous medium gas permeability, all in a linear manner.