This paper proposes a new nonconforming finite difference streamline diffusion method to solve incompressible time-dependent Navier-Stokes equations with a high Reynolds number. The backwards difference in time and th...This paper proposes a new nonconforming finite difference streamline diffusion method to solve incompressible time-dependent Navier-Stokes equations with a high Reynolds number. The backwards difference in time and the Crouzeix-Raviart （CR） element combined with the P0 element in space are used. The result shows that this scheme has good stabilities and error estimates independent of the viscosity coefficient.展开更多
水面起飞性能是水面飞行器的基本性能,也是总体技术的核心,涉及多个学科领域。水陆两栖飞机水面高速滑行水动力性能与排水型船不同,具有速度高、运动复杂等特点,高速滑行时一方面受到较大的水动升力,另一方面受到机翼的升力。结合水陆...水面起飞性能是水面飞行器的基本性能,也是总体技术的核心,涉及多个学科领域。水陆两栖飞机水面高速滑行水动力性能与排水型船不同,具有速度高、运动复杂等特点,高速滑行时一方面受到较大的水动升力,另一方面受到机翼的升力。结合水陆两栖飞机水面高速滑行特点,利用雷诺平均法(Reynolds average navier-stokes, RANS)数值方法和重叠网格技术对水陆两栖飞机全机模型开展数值仿真模拟,分析了自由液面水气分布、机身底部压力分布特征,并将阻力、姿态和升沉与水池模型试验结果进行对比,验证了数值方法的准确性,为水陆两栖飞机静水滑行水动性能数值预报提供技术基础。展开更多
At T-junctions, where hot and cold streams flowing in pipes join and mix, significant temperature fluctuations can be created in very close neighborhood of the pipe walls. The wall temperature fluctuations cause cycli...At T-junctions, where hot and cold streams flowing in pipes join and mix, significant temperature fluctuations can be created in very close neighborhood of the pipe walls. The wall temperature fluctuations cause cyclical thermal stresses which may induce fatigue cracking. Temperature fluctuation is of crucial importance in many engineering applications and especially in nuclear power plants. This is because the phenomenon leads to thermal fatigue and might subsequently result in failure of structural material. Therefore, the effects of temperature fluctuation in piping structure at mixing junctions in nuclear power systems cannot be neglected. In nuclear power plant, piping structure is exposed to unavoidable temperature differences in a bid to maintain plant operational capacity. Tightly coupled to temperature fluctuation is flow turbulence, which has attracted extensive attention and has been investigated worldwide since several decades. The focus of this study is to investigate the effects of injection pipe orientation on flow mixing and temperature fluctuation for fluid flow downstream a T-junction. Computational fluid dynamics (CFD) approach was applied using STAR CCM+ code. Four inclination angles including 0 (90), 15, 30 and 45 degrees were studied and the mixing intensity and effective mixing zone were investigated. K-omega SST turbulence model was adopted for the simulations. Results of the analysis suggest that, effective mixing of cold and hot fluid which leads to reduced and uniform temperature field at the pipe wall boundary, is achieved at 0 (90) degree inclination of the branch pipe and hence may lower thermal stress levels in the structural material of the pipe. Turbulence mixing, pressure drop and velocity distribution were also found to be more appreciable at 0 (90) degree inclination angle of the branch pipe relative to the other orientations studied.展开更多
将两方程k-ωSST湍流模型和Sagaut的混合尺度亚格子模型通过一个混合函数相结合,构造出一种混合大涡/雷诺平均N-S方程模拟方法(hybird large eddy simulation/reynolds-averaged navier-stokes,HybridLES/RANS),采用这种混合模拟方法结...将两方程k-ωSST湍流模型和Sagaut的混合尺度亚格子模型通过一个混合函数相结合,构造出一种混合大涡/雷诺平均N-S方程模拟方法(hybird large eddy simulation/reynolds-averaged navier-stokes,HybridLES/RANS),采用这种混合模拟方法结合5阶WENO格式对Ma=2.8平板湍流边界层进行了数值模拟,并在计算区域上游入口处采用"回收/调节"方法生成湍流脉动边界条件,通过考查RANS区域向LES区域的过渡参数及网格分辨率对这种混合模拟方法进行了评价.计算结果表明:该文采用的混合模拟方法可以捕捉到湍流边界层中的大尺度结构且入口边界层平均参数不会发生漂移,混合函数应当将RANS区域和LES区域的过渡点设置在对数律层和尾迹律层的交界处,而过渡应当迅速以获得正确的雷诺剪切应力分布,在该文采用的模型及数值方法的条件下,流向及展向的网格小至与Escudier混合长相当时,能够获得可以接受的脉动速度的单点-二阶统计值.展开更多
Aerodynamic noise due to interaction between incoming turbulence and rotating blades is an important component in the wind turbine noise. The rod-airfoil configuration is used to investigate the interactive phenomenon...Aerodynamic noise due to interaction between incoming turbulence and rotating blades is an important component in the wind turbine noise. The rod-airfoil configuration is used to investigate the interactive phenomenon experimentally and nu- merically. Distribution of unsteady pressure on the airfoil surface is measured for different rod positions and airfoil attack angles. Two National Advisory Committee for Aeronatics （NACA） airfoils, NACA0012 and NACA0018, and two wind turbine airfoils, S809 and S825 are investigated. In addition, for low angles of attack, the flow field around the airfoil＇s leading edge is investigated with the particle image velocimetry （PIV）. The experimental results indicate that unsteady pressure disturbances on the airfoil surface are related to the rod vortex shedding. Meanwhile, the interaction flow field of the rod and NACA0012 airfoil is simulated with the unsteady Reynolds averaged Navier-Stokes method （URANS）, and the obtained pressure spectra are compared with the experimental results.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11271273 and 11271298)
文摘This paper proposes a new nonconforming finite difference streamline diffusion method to solve incompressible time-dependent Navier-Stokes equations with a high Reynolds number. The backwards difference in time and the Crouzeix-Raviart （CR） element combined with the P0 element in space are used. The result shows that this scheme has good stabilities and error estimates independent of the viscosity coefficient.
文摘水面起飞性能是水面飞行器的基本性能,也是总体技术的核心,涉及多个学科领域。水陆两栖飞机水面高速滑行水动力性能与排水型船不同,具有速度高、运动复杂等特点,高速滑行时一方面受到较大的水动升力,另一方面受到机翼的升力。结合水陆两栖飞机水面高速滑行特点,利用雷诺平均法(Reynolds average navier-stokes, RANS)数值方法和重叠网格技术对水陆两栖飞机全机模型开展数值仿真模拟,分析了自由液面水气分布、机身底部压力分布特征,并将阻力、姿态和升沉与水池模型试验结果进行对比,验证了数值方法的准确性,为水陆两栖飞机静水滑行水动性能数值预报提供技术基础。
文摘At T-junctions, where hot and cold streams flowing in pipes join and mix, significant temperature fluctuations can be created in very close neighborhood of the pipe walls. The wall temperature fluctuations cause cyclical thermal stresses which may induce fatigue cracking. Temperature fluctuation is of crucial importance in many engineering applications and especially in nuclear power plants. This is because the phenomenon leads to thermal fatigue and might subsequently result in failure of structural material. Therefore, the effects of temperature fluctuation in piping structure at mixing junctions in nuclear power systems cannot be neglected. In nuclear power plant, piping structure is exposed to unavoidable temperature differences in a bid to maintain plant operational capacity. Tightly coupled to temperature fluctuation is flow turbulence, which has attracted extensive attention and has been investigated worldwide since several decades. The focus of this study is to investigate the effects of injection pipe orientation on flow mixing and temperature fluctuation for fluid flow downstream a T-junction. Computational fluid dynamics (CFD) approach was applied using STAR CCM+ code. Four inclination angles including 0 (90), 15, 30 and 45 degrees were studied and the mixing intensity and effective mixing zone were investigated. K-omega SST turbulence model was adopted for the simulations. Results of the analysis suggest that, effective mixing of cold and hot fluid which leads to reduced and uniform temperature field at the pipe wall boundary, is achieved at 0 (90) degree inclination of the branch pipe and hence may lower thermal stress levels in the structural material of the pipe. Turbulence mixing, pressure drop and velocity distribution were also found to be more appreciable at 0 (90) degree inclination angle of the branch pipe relative to the other orientations studied.
文摘将两方程k-ωSST湍流模型和Sagaut的混合尺度亚格子模型通过一个混合函数相结合,构造出一种混合大涡/雷诺平均N-S方程模拟方法(hybird large eddy simulation/reynolds-averaged navier-stokes,HybridLES/RANS),采用这种混合模拟方法结合5阶WENO格式对Ma=2.8平板湍流边界层进行了数值模拟,并在计算区域上游入口处采用"回收/调节"方法生成湍流脉动边界条件,通过考查RANS区域向LES区域的过渡参数及网格分辨率对这种混合模拟方法进行了评价.计算结果表明:该文采用的混合模拟方法可以捕捉到湍流边界层中的大尺度结构且入口边界层平均参数不会发生漂移,混合函数应当将RANS区域和LES区域的过渡点设置在对数律层和尾迹律层的交界处,而过渡应当迅速以获得正确的雷诺剪切应力分布,在该文采用的模型及数值方法的条件下,流向及展向的网格小至与Escudier混合长相当时,能够获得可以接受的脉动速度的单点-二阶统计值.
基金Project supported by the National Basic Research Program of China (973 Program) (No. 2007CB714604)
文摘Aerodynamic noise due to interaction between incoming turbulence and rotating blades is an important component in the wind turbine noise. The rod-airfoil configuration is used to investigate the interactive phenomenon experimentally and nu- merically. Distribution of unsteady pressure on the airfoil surface is measured for different rod positions and airfoil attack angles. Two National Advisory Committee for Aeronatics （NACA） airfoils, NACA0012 and NACA0018, and two wind turbine airfoils, S809 and S825 are investigated. In addition, for low angles of attack, the flow field around the airfoil＇s leading edge is investigated with the particle image velocimetry （PIV）. The experimental results indicate that unsteady pressure disturbances on the airfoil surface are related to the rod vortex shedding. Meanwhile, the interaction flow field of the rod and NACA0012 airfoil is simulated with the unsteady Reynolds averaged Navier-Stokes method （URANS）, and the obtained pressure spectra are compared with the experimental results.
