Study Of The Near-wall Flow Field In The Turbulent Tube Based On Particulate Deposition

Recently high attention is paid to the research on the problem of diesel particulates emission at home and abroad, but up to now, deposition regularity of diesel particulates in exhaust pipe and its influence factors which we known are very limited. As particle movement depends to a great extent on airflow motion in pipeline, in order to supply foundation and basis for the research of particulate deposition regularity, the study of structural characteristics and influence factors of pipeline flow field especially near-wall flow field is quite necessary.According to the need of research on diesel particulates thermophoresis deposition and turbulent deposition, in this paper, distribution characteristics, influence factors and its variation regularity of near-wall flow field about steady flow and pulsating flow in straight round pipe are studied by FLUENT. In the steady flow, the influence factors of near-wall temperature field and turbulent kinetic energy field of straight round pipe such as air inlet velocity, inlet temperature and pipe diameter; in the pulsating flow, the influence factors are pulsation amplitude and pulsation frequency.In light of the complexity of diesel exhaust system, exhaust flow field of several kind of different structure pipeline, for example, bent pipe, sudden expand pipe, bifurcation pipe etc, are analyzed, distribution characteristics, influence factors and variation regularity of near-wall flow field is regarded as key research. Focusing on the flow field of outer wall surface and inter wall surface of violent changes flow parameters bend where flow field distribution impacts on particulates deposition, the effect of inlet velocity and bend angle degree on temperature field and turbulent kinetic energy field are analyzed, and then, the temperature field, velocity field and turbulent kinetic energy field of sudden-expansion point under different expansion degree of sudden expand pipe are discussed, at last, the flow field of first and second grade bifurcation pipe is studied, especially the near-wall flow field of sudden-expansion point.In this paper, distribution characteristics, influence facts and variation regularity of near-wall flow field in several different structure pipelines are obtained. Theoretical basis and research foundation of diesel particulates deposition regularity in different pipe structures exhaust system are supplied by the research results.