For high Re number flows,a new computational fluid dynamics （CFD） validation method,namely,wall-surface compatibility criteria method and also called Gao＇s criteria,is proposed to verify near wall flows.As examples...For high Re number flows,a new computational fluid dynamics （CFD） validation method,namely,wall-surface compatibility criteria method and also called Gao＇s criteria,is proposed to verify near wall flows.As examples,Gao＇s criteria method and other two CFD verification methods （analytic solutions method and grid convergence analysis） are used to verify FLUENT＇s near wall flows solutions for two-dimensional incompressible laminar stagnation-point flows.The exact solution of the Navier-Stokes equations for laminar stagnation-point flows satisfy accurately all Gao＇s criteria,numerical simulations of laminar stagnation-point flows show that when physical parameters （the pressure coefficient and the Stanton number at wall surface） achieve convergence with more and more fine-screen grid,a part of Gao＇s criteria are not satisfied.展开更多
The purpose of this article is to review recent PIV Studies from the basic to hybrid analysis, focusing on explaining epoch-making development of PIV. The overwhelming advantage of PIV over other velocity measurement ...The purpose of this article is to review recent PIV Studies from the basic to hybrid analysis, focusing on explaining epoch-making development of PIV. The overwhelming advantage of PIV over other velocity measurement methods is that it enables instantaneous and simultaneous velocity measurement of whole flow fields. We roughly classify PIV development and/or progress into the following five categories; A) Basics of PIV and post-processing. B) Simultaneous measurement of velocity and temperature, and 3D-PIV. C) Application to multiphase turbulent flows. D) Application to fluid machinery. E) Hybridization of PIV and CFD. This paper introduces the epoch-making research results from papers published in international journals as milestones related to (A) to (E), and concludes with additional forecast of future development of PIV research.展开更多
Gymnarchus niloticus, a typical freshwater fish, swims by undulations of a long-based dorsal fin aided by the two pectoral fins, while commonly it holds its body rigid and straight. The long flexible dorsal fin is the...Gymnarchus niloticus, a typical freshwater fish, swims by undulations of a long-based dorsal fin aided by the two pectoral fins, while commonly it holds its body rigid and straight. The long flexible dorsal fin is the main propulsor of G niloticus; it has also considerable influence on the streamline profile. This paper proposes a CFD approach to validate that the natural arrangement of the propulsive dorsal fin is optimal. Using morphological data and a smoothness-keeping algorithm, the dorsal fin is ‘virtually＇ moved forward and backward with several displacements from the natural location. For each case, we reconstruct geometry, generate CFD grids, and calculate the pressure, viscous and total drag coefficients respectively. The results show that the pressure and total drag coefficients increase whether the dorsal fin is displaced forward or backward, and that greater displacement from its original position leads to greater pressure and total drag coefficients. This suggests that the natural position of the dorsal fin is significant for maintaining the fish＇s streamline profile and reducing drag.展开更多
采用重整化群(renormalization group,RNG)理论k-ε湍流模型以及流体体积(volume of fluid,VOF)函数气液两相流模型对有压管道局部高点滞留气团的排出进行数值模拟,计算出气泡开始出现破碎的临界流速v1、气泡开始有效破碎且小气泡被带...采用重整化群(renormalization group,RNG)理论k-ε湍流模型以及流体体积(volume of fluid,VOF)函数气液两相流模型对有压管道局部高点滞留气团的排出进行数值模拟,计算出气泡开始出现破碎的临界流速v1、气泡开始有效破碎且小气泡被带走的临界流速v2以及气泡被一次性带走的临界流速v3。此外,通过粒子图像测速(particle image velocimetry,PIV)系统测试了3种临界速度下的流场结构。研究表明:有压管道下降角度增大,3种临界流速均增大;随着滞留气团的体积变大,临界流速v1减小,而临界流速v2和v3均增大;在管道直径、下降角、气量均不变的情况下,临界流速v3比v2大2%~10%,但临界流速v1远小于v2。展开更多
The internal flow fields in a compact return diffuser under strong part-load conditions are investigated both numerically and experimentally.For numerical simulation,three-dimensional unsteady Reynolds-Averaged Navier...The internal flow fields in a compact return diffuser under strong part-load conditions are investigated both numerically and experimentally.For numerical simulation,three-dimensional unsteady Reynolds-Averaged Navier–Stokes equations are solved on high-quality structured grids in conjunction with the shear stress transport k–turbulence model by employing the computational fluid dynamics(CFD)software ANSYS-Fluent 14.5.For flow field measurements,a special test rig is designed and the two-dimensional particle image velocimetry(PIV)measurements are conducted in the diffuser midplane to capture the complex flow field and for validation of the CFD results.The analysis of the results has been focused on the flow structure in the diffuser,especially under part-load conditions.The detailed comparison between CFD and PIV results is performed.Vortical flow and recirculation flow patterns in the diffuser are captured and analyzed.Large flow separation and backflow appear under the part-load flow conditions.This paper provides a good data set for developing as well as evaluating the accuracy of various CFD models for capturing the complex flow field in a compact return diffuser used with multistage pumps.展开更多
基金Sponsored by the National Natural Science Foundation of China(10702009)
文摘For high Re number flows,a new computational fluid dynamics （CFD） validation method,namely,wall-surface compatibility criteria method and also called Gao＇s criteria,is proposed to verify near wall flows.As examples,Gao＇s criteria method and other two CFD verification methods （analytic solutions method and grid convergence analysis） are used to verify FLUENT＇s near wall flows solutions for two-dimensional incompressible laminar stagnation-point flows.The exact solution of the Navier-Stokes equations for laminar stagnation-point flows satisfy accurately all Gao＇s criteria,numerical simulations of laminar stagnation-point flows show that when physical parameters （the pressure coefficient and the Stanton number at wall surface） achieve convergence with more and more fine-screen grid,a part of Gao＇s criteria are not satisfied.
文摘The purpose of this article is to review recent PIV Studies from the basic to hybrid analysis, focusing on explaining epoch-making development of PIV. The overwhelming advantage of PIV over other velocity measurement methods is that it enables instantaneous and simultaneous velocity measurement of whole flow fields. We roughly classify PIV development and/or progress into the following five categories; A) Basics of PIV and post-processing. B) Simultaneous measurement of velocity and temperature, and 3D-PIV. C) Application to multiphase turbulent flows. D) Application to fluid machinery. E) Hybridization of PIV and CFD. This paper introduces the epoch-making research results from papers published in international journals as milestones related to (A) to (E), and concludes with additional forecast of future development of PIV research.
文摘Gymnarchus niloticus, a typical freshwater fish, swims by undulations of a long-based dorsal fin aided by the two pectoral fins, while commonly it holds its body rigid and straight. The long flexible dorsal fin is the main propulsor of G niloticus; it has also considerable influence on the streamline profile. This paper proposes a CFD approach to validate that the natural arrangement of the propulsive dorsal fin is optimal. Using morphological data and a smoothness-keeping algorithm, the dorsal fin is ‘virtually＇ moved forward and backward with several displacements from the natural location. For each case, we reconstruct geometry, generate CFD grids, and calculate the pressure, viscous and total drag coefficients respectively. The results show that the pressure and total drag coefficients increase whether the dorsal fin is displaced forward or backward, and that greater displacement from its original position leads to greater pressure and total drag coefficients. This suggests that the natural position of the dorsal fin is significant for maintaining the fish＇s streamline profile and reducing drag.
基金supported by the National Natural Science Foundation of China(Grant No.51279069)the Natural Science Foundation of Jiangsu Province(Grant No.BK20131256)
文摘The internal flow fields in a compact return diffuser under strong part-load conditions are investigated both numerically and experimentally.For numerical simulation,three-dimensional unsteady Reynolds-Averaged Navier–Stokes equations are solved on high-quality structured grids in conjunction with the shear stress transport k–turbulence model by employing the computational fluid dynamics(CFD)software ANSYS-Fluent 14.5.For flow field measurements,a special test rig is designed and the two-dimensional particle image velocimetry(PIV)measurements are conducted in the diffuser midplane to capture the complex flow field and for validation of the CFD results.The analysis of the results has been focused on the flow structure in the diffuser,especially under part-load conditions.The detailed comparison between CFD and PIV results is performed.Vortical flow and recirculation flow patterns in the diffuser are captured and analyzed.Large flow separation and backflow appear under the part-load flow conditions.This paper provides a good data set for developing as well as evaluating the accuracy of various CFD models for capturing the complex flow field in a compact return diffuser used with multistage pumps.
