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61.
The flow field of a flapping airfoil in Low Reynolds Number (LRN) flow regime is associated with complex nonlinear vortex shedding and viscous phenomena. The respective fluid dynamics of such a flow is investigated here through Computational Fluid Dynamics (CFD) based on the Finite Volume Method (FVM). The governing equations are the unsteady, incompressible two-dimensional Navier-Stokes (N-S) equations. The airfoil is a thin ellipsoidal geometry performing a modified figure-of-eight-like flapping pattern. The flow field and vortical patterns around the airfoil are examined in detail, and the effects of several unsteady flow and system parameters on the flow characteristics are explored. The investigated parameters are the amplitude of pitching oscillations, phase angle between pitching and plunging motions, mean angle of attack, Reynolds number (Re), Strouhal number (St) based on the translational amplitudes of oscillations, and the pitching axis location (x/c). It is shown that these parameters change the instantaneous force coefficients quantitatively and qualitatively. It is also observed that the strength, interaction, and convection of the vortical structures surrounding the airfoil are significantly affected by the variations of these parameters. 相似文献
62.
Scale up of gas-solid circulating fluidized bed (CFB) risers poses many challenges to researchers.In this paper,CFD investigation of hydrodynamic scaling laws for gas-solid riser flow was attempted on the basis of two-fluid model simulations,in particular,the recently developed empirical scaling law of Qi,Zhu,and Huang (2008).A 3D computational model with periodic boundaries was used to perform numerical experiments and to study the effect of various system and operating parameters in hydrodynamic scaling o... 相似文献
63.
A high-temperature turbulent jet in a cold crossflow is investigated with the help of two scale-resolving simulation approaches. This work aims at improving the methodologies used to predict the thermal footprint of exhaust gases issuing from helicopter engines onto the fuselage. Specific attention is brought to the capability of scale resolving simulations to correctly reproduce flow dynamics and turbulent mixing. Mean flow features, turbulent quantities and temperature fields are compared and validated against wind tunnel test measurements. In addition, the present work highlights the importance of synthetic turbulence injection at pipe inlet to obtain a fair prediction of both flow dynamics and temperature field. 相似文献
64.
Thermal-hydraulic conditions in a partially uncovered nuclear fuel assembly mock-up are studied with particular focus on the influence of the horizontal air flow above the rod bundle. The investigations are performed at the ALADIN test facility, which models a boiling water reactor fuel assembly at a 1:1 scale both axially and radially. In the scenario studied, the main heat transfer mechanisms – conduction, convection and radiation – are strongly coupled and all are of similar importance. A combination of measurements and CFD simulations serves to analyze the heat transfer processes in detail. Contrary to previous studies in this field, all heat transfer mechanisms were considered in the simulation with sophisticated models. The numerical results show a good agreement with the measurements, given the inevitable differences between the approaches. Although the successive evaporation of cooling water in a fuel assembly is a transient, multiphase process, the steady, single-phase simulation yields acceptable results. While single effects are overestimated in the simulation, the important dependencies are predicted similarly. A general result is that the maximum cladding temperature rises with decreasing water level. Further results indicate an impact of the horizontal air flow on the residual heat removal for moderate rod powers. Higher horizontal velocities above the fuel assembly lead to slightly higher temperatures inside. A characteristic flow field forms in the test facility that prevails for all studied water levels and horizontal velocities. However, it has only a minor effect on the temperature distribution in the central rod bundle. By combining experiments and numerical simulations, the study provides important information about the decisive parameters for the heat exchange in a spent fuel pool in case of an accident with loss of cooling. The exposed length of the fuel rods is of much more importance than the magnitude of the horizontal velocity above the fuel assembly. 相似文献
65.
谱体积方法是一种本质上解决网格依赖性的高精度CFD计算方法,本文研究了二维Euler方程的谱体积方法,提出一种基于切比雪夫多项式的单元分割方法,建立了基于WENO的变量限制器方法,并发展了结合谱体积和控制体的问题单元标记方法.采用15°超声速压缩拐角和NACA0012跨声速流动两个典型算例进行验证,结果表明,该分区方法具有更好的计算精度,标记方法可有效识别不连续区域,在较少的网格下即可获得与密网格传统有限体积法相当的计算精度. 相似文献
66.
The objective of this work is to develop a sliding interface method for simulations involving relative grid motion that is fast and efficient and involves no grid deformation, remeshing, or hole cutting. The method is implemented into a parallel, node‐centred finite volume, unstructured viscous flow solver. The rotational motion is accomplished by rigidly rotating the subdomain representing the moving component. At the subdomain interface boundary, the faces along the interface are extruded into the adjacent subdomain to create new volume elements forming a one‐cell overlap. These new volume elements are used to compute a flux across the subdomain interface. An interface flux is computed independently for each subdomain. The values of the solution variables and other quantities for the nodes created by the extrusion process are determined by linear interpolation. The extrusion is done so that the interpolation will maintain information as localized as possible. The grid on the interface surface is arbitrary. The boundary between the two subdomains is completely independent from one another; meaning that they do not have to connect in a one‐to‐one manner and no symmetry or pattern restrictions are placed on the grid. A variety of numerical simulations were performed on model problems and large‐scale applications to examine conservation of the interface flux. Overall solution errors were found to be comparable to that for fully connected and fully conservative simulations. Excellent agreement is obtained with theoretical results and results from other solution methodologies. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
67.
Comparative Study of Plasma Spray Flow Fields and Particle Behavior Near to Flat Inclined Substrates
Numerical models have been developed using computational fluid dynamics (CFD) analysis program FLUENT V6.02© to investigate the effect of the substrate on the behavior of the plasma flow fields and in-flight particles. Simulations are performed for cases where flat substrates are either present or absent, for the former, the substrate is oriented perpendicularly or inclined to the torch axis. It is shown that although the presence of perpendicular or inclined substrate significantly influences the plasma flow fields at the vicinity of the substrate, the particle behavior remain relatively unaffected. The insignificant effect of the substrate on particle behavior is qualitatively verified by experimental observation using SprayWatch© imaging diagnostics equipment. Images captured by the equipment confirm that the particles travel through the plasma plume with high momentum and show no sudden change in theirtrajectories right before impacting the substrate. Both the numerical and experimental findings show that the freestream model is sufficiently detailed for future work of this nature. 相似文献
68.
The flow structure in a flat plate integrated collector storage device, with recirculation of the storage water, is studied experimentally and theoretically. To facilitate flow visualization, an experimental device was constructed by transparent material (Plexiglas). Flow velocities and fluctuations are measured, using a LDV system. A three-dimensional CFD-model was developed using the FLUENT code. The standard k–ω model is selected as the most appropriate. The model is validated, with good agreement, against experimental measurements. Furthermore, copper tubes, in the form of embedded heat exchanger, are placed inside the device and another similar 3D model was developed. The model was used to examine the behavior of the system, when the service water enters the heat exchanger, thus being indirectly heated by the stored hot water. It is shown that the outlet temperature of the service water is enough higher, when recirculation occurs. 相似文献
69.
尾缘凹陷轴流风轮内流特性分析与降噪研究 总被引:1,自引:0,他引:1
为减少空调室外机用低压轴流风轮叶片的颤振,改善音质,降低噪音和电机功率。本文设计了尾缘凹陷新型三叶轴流风轮,同时除对前缘局部加厚处理外,对叶片其他区域整体减薄。文中采用Navier-Stokes方程对新风轮和原风轮的内流及气动特性进行了三维数值模拟,同时对两者的流量压力曲线和噪音频谱进行了实验研究。研究表明:对轴流风轮叶片尾缘进行凹陷设计,对前缘以外的区域减薄设计,能够减轻风轮重量,降低电机负荷同时减弱转子尾迹;对叶轮前缘进行局部加厚处理可以减小叶尖颤振,降低叶片旋转频率峰值噪音,从整体上降低噪音,改善音质。 相似文献
70.