基于动网格技术及浸润边界法的飞灰沉积数值模拟研究
发布时间：2019-03-05 12:57
【摘要】：锅炉的尾部烟道和水平烟道受热面上的飞灰沉积现象十分普遍。国内外利用数值模拟方法对锅炉内飞灰沉积的研究由来已久。随着对飞灰输运、碰撞以及沉积等相关机理的深入研究,数值模型和算法的不断改进,飞灰沉积数值模拟研究目前进入到了比较成熟的阶段。早期的研究主要借助自编程代码作为研究手段,随着商业数值软件如Fluent、CFX等的出现,大量研究人员开始使用方便快捷的模块化操作对沉积现象进行研究并获得了一些成果。商业软件在物理建模,控制方求解,两相耦合,颗粒输运等方面给予用户极大的方便和一定程度的选择,但是,在某些特殊情况下由于功能的限制并不能完全满足用户的要求,自编程代码求解飞灰沉积问题仍然有着不可替代的作用。本文首先对飞灰沉积数值模拟研究方面进行了简要的回顾和总结,最后分析发现,在沉积机理过程以及沉积判定等方面,研究内容较为丰富,沉积过程主要涉及输运、黏附、惯性碰撞等,而沉积判定主要有速度模型,粘度模型和力准则模型三种判定准则。研究方式主要以自编程代码完成,也有使用商用软件Fluent编写UDF代码完成飞灰沉积判定过程。本文主要通过两种方式对飞灰沉积过程进行了研究,分别是:Fluent软件借助UDF代码,利用动网格模块实现飞灰沉积过程模拟;利用C++自编程代码,离散分步方程,借助IBM浸润边界法对飞灰沉积过程进行模拟。利用两种方式得出数值计算结果之后,与沉降炉所得内蒙古通辽褐煤灰试验结果进行了对比比较。试验结果显示,随着二次风流速的增加,圆形探针上飞灰沉积高度逐渐增加;更改探针直径后,沉积高度变化不大,各个时刻下小直径探针上沉积高度略高于大直径探针上的沉积高度。两种数值模拟方式所得结果与试验结果对比后发现,在沉积高度方面,动网格技术所得数值结果与试验结果贴合更好,而IBM浸润边界法在前期的沉积趋势不明显,增长缓慢,后期的增长逐渐开始与试验结果吻合;在沉积层形貌方面,动网格技术的沉积层更显光滑,但是形貌的边界呈窄尖状,与试验结果不符,IBM浸润边界法所得的沉积层形貌略显粗糙。动网格技术与IBM浸润边界法的计算效率相差较大,同样为90000左右网格数下的模型,对同一算例,IBM浸润边界法计算效率比动网格技术快了近10倍。在实际应用中,要根据合适的情况选取合适的数值计算方法。
[Abstract]:Fly ash deposition on the heating surface of boiler tail flue and horizontal flue is very common. The study of fly ash deposition in boiler has been studied for a long time by using numerical simulation method at home and abroad. With the in-depth study of fly ash transport, collision and deposition mechanism and the continuous improvement of numerical model and algorithm, the numerical simulation of fly ash deposition has entered a relatively mature stage. With the emergence of commercial numerical software such as Fluent,CFX, a large number of researchers began to use convenient and rapid modular operation to study the deposition phenomenon and obtained some achievements. Commercial software provides users with great convenience and a certain degree of choice in physical modeling, control solution, two-phase coupling, particle transport and so on. However, in some special cases, due to the limitation of function, it can not fully meet the requirements of users. Self-programming code still plays an irreplaceable role in solving the problem of fly ash deposition. In this paper, the numerical simulation of fly ash deposition is briefly reviewed and summarized in this paper. Finally, it is found that the deposition process is rich in deposition mechanism and deposition judgment, and the deposition process is mainly related to transport, adhesion, and so on. Inertial collision and so on. There are three criteria to determine deposition, such as velocity model, viscosity model and force criterion model. The research method is mainly completed by self-programming code, but also using commercial software Fluent to write UDF code to complete the determination process of fly ash deposition. In this paper, the process of fly ash deposition is studied in two ways: the Fluent software realizes the simulation of fly ash deposition process with the aid of UDF code and dynamic grid module; The process of fly ash deposition is simulated by using C self-programming code, discrete step equation and IBM infiltration boundary method. The numerical results obtained by two methods are compared with the experimental results of Tongliao lignite ash in Inner Mongolia obtained by settling furnace. The experimental results show that with the increase of secondary air velocity, the height of fly ash deposition on circular probe increases gradually. After changing the diameter of the probe, the deposition height does not change much, and the deposition height on the small diameter probe is slightly higher than the deposition height on the large diameter probe at each time. The results obtained by the two numerical simulation methods are compared with the experimental results. It is found that the numerical results obtained by the dynamic mesh technique agree better with the experimental results in terms of sedimentation height, while the deposition trend of the IBM infiltration boundary method is not obvious and the growth rate is slow. The growth of the later period began to coincide with the results of the experiment. In terms of the morphology of the deposition layer, the dynamic mesh technique is more smooth, but the boundary of the deposit layer is narrow pointed, which is not consistent with the experimental results. The morphology of the deposition layer obtained by the IBM infiltration boundary method is slightly rough. The computational efficiency of the moving mesh method is different from that of the IBM infiltration boundary method, which is about 90000 mesh numbers. For the same example, the computational efficiency of the IBM infiltration boundary method is nearly 10 times faster than that of the moving mesh method. In practical application, the appropriate numerical calculation method should be selected according to the appropriate situation.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK221
，
本文编号：2434926
[Abstract]:Fly ash deposition on the heating surface of boiler tail flue and horizontal flue is very common. The study of fly ash deposition in boiler has been studied for a long time by using numerical simulation method at home and abroad. With the in-depth study of fly ash transport, collision and deposition mechanism and the continuous improvement of numerical model and algorithm, the numerical simulation of fly ash deposition has entered a relatively mature stage. With the emergence of commercial numerical software such as Fluent,CFX, a large number of researchers began to use convenient and rapid modular operation to study the deposition phenomenon and obtained some achievements. Commercial software provides users with great convenience and a certain degree of choice in physical modeling, control solution, two-phase coupling, particle transport and so on. However, in some special cases, due to the limitation of function, it can not fully meet the requirements of users. Self-programming code still plays an irreplaceable role in solving the problem of fly ash deposition. In this paper, the numerical simulation of fly ash deposition is briefly reviewed and summarized in this paper. Finally, it is found that the deposition process is rich in deposition mechanism and deposition judgment, and the deposition process is mainly related to transport, adhesion, and so on. Inertial collision and so on. There are three criteria to determine deposition, such as velocity model, viscosity model and force criterion model. The research method is mainly completed by self-programming code, but also using commercial software Fluent to write UDF code to complete the determination process of fly ash deposition. In this paper, the process of fly ash deposition is studied in two ways: the Fluent software realizes the simulation of fly ash deposition process with the aid of UDF code and dynamic grid module; The process of fly ash deposition is simulated by using C self-programming code, discrete step equation and IBM infiltration boundary method. The numerical results obtained by two methods are compared with the experimental results of Tongliao lignite ash in Inner Mongolia obtained by settling furnace. The experimental results show that with the increase of secondary air velocity, the height of fly ash deposition on circular probe increases gradually. After changing the diameter of the probe, the deposition height does not change much, and the deposition height on the small diameter probe is slightly higher than the deposition height on the large diameter probe at each time. The results obtained by the two numerical simulation methods are compared with the experimental results. It is found that the numerical results obtained by the dynamic mesh technique agree better with the experimental results in terms of sedimentation height, while the deposition trend of the IBM infiltration boundary method is not obvious and the growth rate is slow. The growth of the later period began to coincide with the results of the experiment. In terms of the morphology of the deposition layer, the dynamic mesh technique is more smooth, but the boundary of the deposit layer is narrow pointed, which is not consistent with the experimental results. The morphology of the deposition layer obtained by the IBM infiltration boundary method is slightly rough. The computational efficiency of the moving mesh method is different from that of the IBM infiltration boundary method, which is about 90000 mesh numbers. For the same example, the computational efficiency of the IBM infiltration boundary method is nearly 10 times faster than that of the moving mesh method. In practical application, the appropriate numerical calculation method should be selected according to the appropriate situation.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK221
，
本文编号：2434926
本文链接：https://www.wllwen.com/kejilunwen/dongligc/2434926.html
