Turbulent Jet in Coflow – ATheoretical Model of Vehicular Plume Exhaust

摘要

Air quality has a substantial influence on scientific research and our daily lives. Traffic emission is the major pollutant source in urban areas. Free-shear jet is a platform helps elucidate the flows and transport processes in the wake after a vehicular tailpipe. There is increasing evidence that turbulence structures in the whole flow are all affected by jet initial conditions, such as Reynolds number at the jet exit. However, most of studies focused on round free jet in the stagnant environment or with extremely low coflow strength, which cannot be used to characterize the effect of background wind. Hence, this paper is conceived to examine the flow characteristics in a turbulent jet as a function of coflow strength. A two dimensional (2D) computational domain was created in the cylindrical coordinates and was solved by standard k–ε model. After validation with previous measurement data, the computational results show that the mean velocity decay along the jet centerline is independent from the initial Reynolds number, which is consistent with the results from Klein et al. (2003). For a jet in coflow, the axial velocity decay is strongly affected by coflow strength. The spreading rate exhibits a linear correlation with the coflow strength. The functional form of the mathematical relation will be further studied.