基于四方程模型的LBE环管湍流换热数值研究

为计算液态铅铋(LBE)在环管内不同加热环境下的湍流换热,基于开源计算流体力学程序OpenFOAM开发了四方程模型求解器4eqnFoam。将LBE在平板和圆管内的预测结果与直接数值模拟结果和实验结果进行对比,验证了求解器的有效性。基于该求解器,分别计算了LBE在外壁绝热内壁加热以及内外壁面等热流加热环管内不同雷诺数下的湍流换热量。结果表明:随着雷诺数的增加,两种加热条件下的无量纲温度脉动、雷诺热流、湍流热扩散作用增大,而平均湍流普朗特数减小;当雷诺数增加到一定程度时,平均湍流普朗特数变化不明显。基于4eqnFoam求解器,可为计算LBE热工水力现象提供更多参考。

基于■模型的液态金属三角形棒束数值传热研究

相比恒定的湍流普朗特数(Pr_(t))模型,四方程模型通过引入湍流时间尺度来考虑液态金属的速度和温度边界层之间的差异性,有望提高具有低普朗特数(Pr)传热特性的液态金属数值传热精度。然而四方程模型的输运形式受限于其复杂的边界条件。为简化湍流变量的边界条件,本研究基于泰勒级数展开和近壁湍流分析方法建立了各向同性四方程■模型。基于开源计算流体力学程序OpenFOAM数值计算了液态金属(Pr=0.01)在三角形排列棒束内不同贝克莱数(Pe)、不同栅距比(P/D)的充分发展流动传热过程。将■模型、Pr_(t)=0.85模型和Kays模型的数值结果与实验关系式进行了对比,结果表明:Pr_(t)=0.85模型过高估计了液态金属的努塞尔数,Kays模型和■模型传热结果介于实验关联式之间;低Pe下Kays模型和■模型预测结果相近,而高Pe下■模型较Kays模型保守;随着雷诺数的增加,平均湍流普朗特数减小;随着栅距比的增加,平均湍流普朗特数增加。基于各向同性四方程■模型,可为简化湍流边界条件和计算液态金属流动传热提供参考。

基于漂移流模型的蒸汽发生器稳态热工水力分析

为研究蒸汽发生器的稳态热工水力特性,建立了四方程漂移流模型,并开发了一维计算程序。对蒸汽发生器U型管管束空间考虑为由一次侧通道、二次侧通道和传热管构成,对一次侧通道和二次侧通道的过冷段采用单相流模型,二次侧通道的沸腾段采用四方程漂移流模型,建立基于交错网格的一阶迎风差分方程,通过热平衡-自然循环压降的交叉迭代计算得到稳态热工水力参数。利用程序计算了秦山300 MW核电厂100%、75%、50%、30%、15%功率稳定运行工况下的热工水力特性,并与RELAP5的计算结果进行比较,两组结果一致性较好。

水下爆炸近自由面空化载荷特性分析

水下爆炸近自由面空化对于冲击波传播、爆炸气泡运动以及水面结构冲击损伤都存在重要影响。目前国内外主要采用单流体模型来处理空化,但是难以精确获得空化演化过程中的溃灭载荷以及空化域内部的流场特征。文中引入考虑相变转换的四方程模型,利用2阶MUSCL-Hancock重构格式和HLLC近似黎曼求解器求解齐次双曲型方程,再采用牛顿迭代法求解相变方程。利用水下爆炸近自由面空化试验对该模型进行了初步验证,获得了空化域的典型运动形态和内部压力载荷特性。并在此基础上探索了不同爆深和药量对空化载荷的影响规律,发现空化域内部压力分布范围较广,并非维持在恒定的饱和蒸汽压附近。文中工作可为水下爆炸空化的深入研究提供参考。

A Four-Level Theory on Energy Transfer of the Light-Harvesting Complex Ⅱ in PS Ⅱ in Higher Plants

With reference to the recent achivements about the structure, spectra and kinetics of light_harvesting complex (LHCⅡ) in PSⅡ of higher plants, a four_level model was provided to simulate the energy transfer process from LHC Ⅱ to the reaction center. On the basis of this model, a set of rate equation was established. Analysis of its algebra solution led to a general picture of energy transfer process in LHC Ⅱ of higher plants and the strong interaction among pigment molecules in this process. Based on the spectra, kinetics and biological structural data providing some information of energy transfer path and energy dissipation mechanism, it has been found that energy transfer mainly happened between the pigments whose energy level was most closely adjacent, the loss of energy had a close relation to the process of energy transfer and tended to increase with the decrease of energy level. The protective mechanism of antenna system was also discussed.

A study of nonlinear biochemical reaction model

The present study deals with the introduction of an alteration in Legendre wavelets method by availing of the Picard iteration method for system of differential equations and named it Legendre wavelet-Picard method （LWPM）. Convergence of the proposed method is also discussed. In order to check the competence of the proposed method, basic enzyme kinetics is considered. Systems of nonlinear ordinary differential equations are formed from the considered enzyme-substrate reaction. The results obtained by the proposed LWPM are compared with the numerical results obtained from Runge-Kutta method of order four （RK-4）. Numerical results and those obtained by LWPM are in excellent conformance, which would be explained by the help of table and figures. The proposed method is easy and simple to implement as compared to the other existing analytical methods used for solving systems of differential equations arising in biology, physics and engineering.