Lattice Boltzmann Method Simulation Of Natural Convection In Circular Space

The circular space is composed by an enclosed circle containing many different kinds of inner structures like concentric cylinder and internal slotted circle.For the former one thought it is simple at its structure,it has a large range of flow structures at different parameters and it is still disputable for its basic solutions.So,it is necessary to do some research about it to reveal the principle of flow patterns and its transitions.For the later one,it is extensively used to cooling down the electric busbars in power plants.However,about its oscillation characteristics,it is still difficult to determine whether it is caused by the deviation of numerical method or by the intrinsic features of this model.So,it is also necessary to do some research about it to divulge the reasons of its oscillation.Lattice Boltzmann method,as a novel method,is now widely used in the research field because of its many advantages.It has the advantage of easy conducted and natural parallel.As a result,it was intensely studied by researchers to simulate many problems like multi-phase,multi-component,porous media and micro-scope problems.In this paper,it was used to study the natural convection in these two circular spaces model.The contents are arranged as follows: Firstly,the flow pattern and transition phenomenon in horizontal concentric cylinders was studied.Comparison between present results and existed results are conducted and the analyzation of transitions and different solutions are carried out.The influences of different parameters like Rayleigh number,Prandtl number and aspect ratio to the flow patterns are studied and the critical Rayleigh number at certain parameters like Prandtl number and aspect ratio are mapped indicating complex transition phenomenon.Secondly,flow and heat transfer in cylinder with internal slotted hollow was also studied.Different flow characters at certain parameters are observed.Two parameters,the Rayleigh number and slotted ratio are studied and their influences to the flow transitions are also discussed.The comparison between present results with SIMPLE method is conducted to discover the reasons of oscillation in this model and the difference of its results with the experiment is also discussed.Based on the contents above,several conclusions can be achieved:(1)The results of present about horizontal cylinders are mostly agreed with the existed literatures and different flow patterns are observed at different parameters.Also the transition of flow patterns with the increase of Rayleigh number is observed and more bouncy the flow becomes also.With the increase of aspect ratio,the boundaries of different flow patterns change and the critical Rayleigh number decreases evidently.Also,the stability of fluid increase with the increase of Prandtl number and at Pr?0.5,the flow keeps the time independent upward flow.(2)The results of present about cylinder with internal slotted hollow are also found accordant with the existed literatures.Dual flow and triple flow are also observed at different parameters and the transition of them appears with the increase of Rayleigh number.As the slotted ratio increase,the critical values of different flow structures change also.(3)The results of two numerical methods(SIMPLE and lattice Boltzmann method)are found mostly in agreement with existed experiments.So,it can be concluded that the oscillation phenomenon in this model is mainly caused by its intrinsic features. Besides that,as the Rayleigh number and slotted ratio increase more,under the assumption of two dimensional flows,it is found that the result of present paper is still agreement with the experiments.