Natural Convection Inside And Outside A Duct And An Open Cavity

Natural convection,a common phenomenon,is extensively present in atmosphere,ocean,earth mantle and general life practice.Such a flow induced by buoyancies is an important mechanism of heat and mass transfer in atmosphere and ocean,building ventilation and pollutant diffusion.The corresponding study may be widely used in engineering and environment science,and thus paid considerable attention by investigators.In particular,dynamics and heat transfer of natural convection inside and outside a duct and a top open cavity have been an important topic in fluid mechanics owing to their extensive applications.Accordingly,this becomes the aim of the study in the thesis.Using scaling analysis,numerical simulation and experiment,the study in the thesis analyzes dynamics and heat transfer of natural convection inside and outside the duct,obtains scaling relations under different regimes,and presents transition route to chaos of natural convection on a top open cavity.The study involves:(1)Discuss dynamics and heat transfer of natural convection inside and outside the duct,obtain and validate scaling relations of the velocity,thickness and transitional time;additionally,analyze the evolution of natural convection inside and outside the duct dependent on time,the Rayleigh number and the aspect ratio based on two dimensional numerical results.(2)Based on three dimensional numerical results,investigate natural convection on the top open cavity,present a transition route to chaos,characterize bifurcations in transition process including the Pitchfork bifurcation,the Hopf bifurcation and the period doubling bifurcation,discuss dynamics and heat transfer,and obtain the law of heat and mass transfer in transition process.(3)Based on two and three dimentional numerical results,investigate natural convection on the groove heated below,describe the Pitchfork bifurcation,the Hopf bifurcation,the period doubling bifurcation and the quasi-periodic bifurcation,analyze dynamics and heat transfer in transition process,and obtain the law of heat and mass transfer under different regimes.(4)Using shadowgraph,observe natural convection on the groove heated below and find the wave phenomenon along the groove;using thermistor,measure time series of the temperature and describe the unsteady flow in comparison with numerical results.The study in the thesis increases understanding of fluid mechanics and heat transfer and obtains the law of heat and mass transfer,which may be used in nature and industry.