本文選題：浸入邊界法 + 大渦模擬　； 參考：《中國科學(xué)院研究生院(過程工程研究所)》2015年博士論文

【摘要】：含有復(fù)雜運(yùn)動(dòng)邊界的流固耦合(fluid-solid interaction, FSI)問題廣泛存在于化工生產(chǎn)過程之中,如攪拌反應(yīng)釜以及顆粒流體兩相流等。盡管計(jì)算流體力學(xué)(computational fluid dynamics, CFD)在近幾十年來有了迅速的發(fā)展,但是精確并高效地模擬含復(fù)雜運(yùn)動(dòng)邊界的流動(dòng)和傳遞現(xiàn)象仍然是巨大的挑戰(zhàn)。近年來,基于歐拉正交網(wǎng)格的浸入邊界法(immersed boundary method, IBM)逐漸成為研究此類問題的主要數(shù)值方法之一。本論文在有限體積／差分方法框架下改進(jìn)了浸入邊界法及其并行算法,并以此實(shí)現(xiàn)了實(shí)驗(yàn)室以至工業(yè)尺度的攪拌反應(yīng)釜中流動(dòng)、傳熱以及顆粒懸浮等過程的模擬,證明了該方法的有效性并展現(xiàn)了廣闊的應(yīng)用前景。論文的主要內(nèi)容與創(chuàng)新點(diǎn)如下：在傳統(tǒng)的IBM模擬中,無滑移邊界條件與速度零散度條件通常不能同時(shí)滿足。本論文對(duì)此提出了改進(jìn)方法,即：壓力修正方程先于體積力源項(xiàng)求解,體積力僅僅散布于浸入邊界的內(nèi)部,同時(shí)采用多重直接力方法使無滑移邊界條件得到更好的滿足,從而避免了上述問題。在標(biāo)準(zhǔn)測試算例中,尤其是在運(yùn)動(dòng)邊界附近,改進(jìn)算法能夠得到比傳統(tǒng)方法更為精確的計(jì)算結(jié)果。在IBM的實(shí)際應(yīng)用中經(jīng)常同時(shí)遇到固定與運(yùn)動(dòng)邊界,傳統(tǒng)方法對(duì)此均采用相同的邊界處理方式,難以充分發(fā)揮其優(yōu)勢。本論文根據(jù)不同壁面的運(yùn)動(dòng)特性選取不同的IBM分別處理靜止壁面與運(yùn)動(dòng)壁面,建立了混合浸入邊界法。對(duì)比算例表明該方法能顯著提高計(jì)算效率并保持計(jì)算精度。本論文借助于CPU (central processing unit) - GPU (graphic processing unit)并行計(jì)算突破了復(fù)雜流動(dòng)模擬中計(jì)算量大的瓶頸,GPU計(jì)算相對(duì)于CPU單核獲得了7～20倍的加速。傳統(tǒng)的IBM在處理運(yùn)動(dòng)邊界時(shí)歐拉網(wǎng)格與拉格朗日網(wǎng)格變量間的傳遞算法并行性較差。對(duì)此,本論文提出了部分速度插值與體積力散布的方式,在不增加通信量的情況下簡化了并行算法。基于這些改進(jìn)工作并結(jié)合大渦模擬(large eddy simulation, LES),高雷諾數(shù)復(fù)雜流固耦合問題的大規(guī)模模擬成為了可能。應(yīng)用上述改進(jìn)的IBM,本論文結(jié)合大渦模擬研究了Rushton攪拌釜內(nèi)的湍流流動(dòng),并與實(shí)驗(yàn)以及其他模擬結(jié)果進(jìn)行了對(duì)比,獲得了合理的速度場和湍流參數(shù)分布,證明該方法是研究攪拌釜中湍流流動(dòng)的有效方法。該方法還進(jìn)一步應(yīng)用于工業(yè)尺度攪拌反應(yīng)釜內(nèi)高粘度流體的流動(dòng)與傳熱模擬,有效預(yù)測了反應(yīng)釜內(nèi)的流場與溫度場信息,為其優(yōu)化設(shè)計(jì)提供了依據(jù)。論文還將改進(jìn)的IBM與離散單元法(discrete element method, DEM)結(jié)合,并應(yīng)用CPU-GPU異構(gòu)超級(jí)計(jì)算實(shí)現(xiàn)了攪拌釜內(nèi)液固兩相流的大規(guī)模顆粒解析模擬,闡明了槳型和擋板等幾何結(jié)構(gòu)對(duì)顆粒分布與運(yùn)動(dòng)方式的影響。通過本論文的改進(jìn),IBM結(jié)合超級(jí)計(jì)算已能夠?qū)崿F(xiàn)工業(yè)規(guī)模的含有復(fù)雜運(yùn)動(dòng)邊界系統(tǒng)的有效模擬,并能深入揭示其流動(dòng)與傳遞過程的細(xì)節(jié),而這方面的進(jìn)一步發(fā)展將為攪拌反應(yīng)釜等重要工業(yè)反應(yīng)器的優(yōu)化設(shè)計(jì)提供強(qiáng)有力的工具。
[Abstract]:Solid coupling containing complex moving boundary flow (fluid-solid interaction FSI) problem exists widely in the chemical production process, such as stirring reactor and particle fluid two-phase flow. Although the computational fluid dynamics (computational fluid, dynamics, CFD) has developed rapidly in recent decades, but the accurate and efficient simulation of complex moving boundary flow and transport phenomena is still a great challenge. In recent years, the immersed boundary method based on Euler orthogonal grid (immersed boundary method, IBM) has gradually become one of the main numerical methods of this problem. In this paper, finite volume / finite difference method under the framework of the improvement of the immersed boundary method and its parallel algorithm, and then the flow stirred tank reactor laboratory and industrial scale, and the particle simulation of heat transfer process, proves that the method is effective and fair Now has a broad application prospects. The main contents and innovations are as follows: in the traditional IBM model, no slip boundary condition and speed zero divergence condition usually cannot be satisfied at the same time. This paper puts forward an improved method, namely: the pressure correction equation before the volume source terms of solution, the internal volume load only scattered in the immersion the border, while using multiple direct force method to non slip boundary condition is better satisfied, so as to avoid the above problems. In the standard test examples, especially in movement near the border, the improved algorithm can get more accurate calculation results than the traditional method. In practical application of IBM often encountered with the moving boundary, the traditional method which adopts boundary treatment in the same way, it is difficult to give full play to its advantages. This paper according to the different characteristics of different wall movement were treated with IBM A stationary wall and wall motion, builds the mixed immersed boundary method. Comparative examples show that this method can significantly improve the computational efficiency and precision. This paper based on the CPU (central processing unit) - GPU (graphic processing unit) parallel computing through complex flow simulation in a large amount of computational bottleneck, GPU compared with the single core CPU obtained a speedup of 7~20 times. The traditional IBM in dealing with moving boundary grid Euler and Lagrange mesh variables transfer between parallel algorithm is poor. Therefore, this thesis proposes some scatter velocity interpolation and volume force, the increase in traffic under the condition of simplified parallel algorithm. These the improvement work combined with the large eddy simulation (large eddy simulation, LES), possible large-scale simulation of high Reynolds number of complex FSI problems. The application of the improved IBM, this paper. Large eddy simulation of turbulent flow in Rushton stirred reactor, and compared with the experimental and other simulation results, obtained the reasonable velocity field and turbulence parameters distribution, prove that the method is effective method of mixing kettle in turbulent flow. The method also should be used to simulate the flow and heat transfer of high viscosity fluid reaction the reactor of industrial scale mixing, effective prediction of reactor flow field and temperature field of information, provides the basis for the optimization design. The paper will also improve the IBM and the discrete element method (discrete element method, DEM and CPU-GPU) with application of heterogeneous supercomputing simulate large-scale particle analysis of liquid-solid two-phase reactor flow mixing, illustrates the influence of impeller type and baffle geometry on the particle distribution and movement patterns. Through the improvement of this paper, combined with the IBM supercomputer has been able to achieve industrial scale The effective simulation of complex motion boundary system and the details of its flow and transfer process can be further revealed. The further development of this aspect will provide a powerful tool for the optimization design of important industrial reactors such as stirred tank reactor.

【學(xué)位授予單位】：中國科學(xué)院研究生院(過程工程研究所)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ019

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