The main purpose of this research is the second-order modeling of flow and turbulent heat flux in nonpremixed methane-air combustion.A turbulent stream of non-premixed combustion in a stoichiometric condition,is numer...The main purpose of this research is the second-order modeling of flow and turbulent heat flux in nonpremixed methane-air combustion.A turbulent stream of non-premixed combustion in a stoichiometric condition,is numerically analyzed through the Reynolds averaged Navier-Stokes(RANS) equations.For modeling radiation and combustion,the discrete ordinates(DO) and eddy dissipation concept model have been applied.The Reynolds stress transport model(RSM) also was used for turbulence modeling.For THF in the energy equation,the GGDH model and high order algebraic model of HOGGDH with simple eddy diffusivity model have been applied.Comparing the numerical results of the SED model(with the turbulent Prandtl 0.85) and the second-order heat flux models with available experimental data follows that applying the second-order models significantly led to the modification of predicting temperature distribution and species mass fraction distribution in the combustion chamber.Calculation of turbulent Prandtl number in the combustion chamber shows that the assumption of Pr_(t) of 0.85 is far from reality and Pr_(t) in different areas varies from 0.4 to 1.2.展开更多
长距离输水管道水力瞬变过程中水体压强达到汽化压强时,将会发生水柱分离现象,水柱弥合将产生异常高压,导致管路振动、变形甚至爆管事故。已有的水柱分离弥合水锤数学模型主要采用特征线法(Method of characteristics,MOC)计算,并且很...长距离输水管道水力瞬变过程中水体压强达到汽化压强时,将会发生水柱分离现象,水柱弥合将产生异常高压,导致管路振动、变形甚至爆管事故。已有的水柱分离弥合水锤数学模型主要采用特征线法(Method of characteristics,MOC)计算,并且很少考虑动态摩阻引起的能量衰减。为提高水柱分离弥合水锤现象的计算精确度和稳定性,基于有限体积法二阶Godunov格式,建立了考虑动态摩阻的离散气体空穴模型(Discrete gas cavity model,DGCM)。为实现管道边界和内部单元的统一计算,提出虚拟边界的处理方法。将该模型模拟结果与实验数据以及已有的稳态摩阻模型的计算结果进行比较,并对网格数、压力修正系数等参数敏感性进行分析。结果表明,本模型能够准确模拟出纯水锤、水柱分离弥合水锤两种情况下瞬变压力,与实验数据基本一致;考虑动态摩阻的瞬态压力计算值与实验数据更吻合;与MOC相比,当库朗数小于1.0时,有限体积法二阶Godunov模型计算结果更准确、更稳定;尤其是,压力修正系数取值0.9及较密网格时数学模型能更为准确地再现实验结果。展开更多
文摘The main purpose of this research is the second-order modeling of flow and turbulent heat flux in nonpremixed methane-air combustion.A turbulent stream of non-premixed combustion in a stoichiometric condition,is numerically analyzed through the Reynolds averaged Navier-Stokes(RANS) equations.For modeling radiation and combustion,the discrete ordinates(DO) and eddy dissipation concept model have been applied.The Reynolds stress transport model(RSM) also was used for turbulence modeling.For THF in the energy equation,the GGDH model and high order algebraic model of HOGGDH with simple eddy diffusivity model have been applied.Comparing the numerical results of the SED model(with the turbulent Prandtl 0.85) and the second-order heat flux models with available experimental data follows that applying the second-order models significantly led to the modification of predicting temperature distribution and species mass fraction distribution in the combustion chamber.Calculation of turbulent Prandtl number in the combustion chamber shows that the assumption of Pr_(t) of 0.85 is far from reality and Pr_(t) in different areas varies from 0.4 to 1.2.
文摘长距离输水管道水力瞬变过程中水体压强达到汽化压强时,将会发生水柱分离现象,水柱弥合将产生异常高压,导致管路振动、变形甚至爆管事故。已有的水柱分离弥合水锤数学模型主要采用特征线法(Method of characteristics,MOC)计算,并且很少考虑动态摩阻引起的能量衰减。为提高水柱分离弥合水锤现象的计算精确度和稳定性,基于有限体积法二阶Godunov格式,建立了考虑动态摩阻的离散气体空穴模型(Discrete gas cavity model,DGCM)。为实现管道边界和内部单元的统一计算,提出虚拟边界的处理方法。将该模型模拟结果与实验数据以及已有的稳态摩阻模型的计算结果进行比较,并对网格数、压力修正系数等参数敏感性进行分析。结果表明,本模型能够准确模拟出纯水锤、水柱分离弥合水锤两种情况下瞬变压力,与实验数据基本一致;考虑动态摩阻的瞬态压力计算值与实验数据更吻合;与MOC相比,当库朗数小于1.0时,有限体积法二阶Godunov模型计算结果更准确、更稳定;尤其是,压力修正系数取值0.9及较密网格时数学模型能更为准确地再现实验结果。
