检索结果-内蒙古大学图书馆

Complexities of the transitional flow Regime Downstream of a Square-Edged Orifice in a Circular Pipe

CHEMICAL ENGINEERING SCIENCE 2025年 310卷

作者： Wadsley, G. K. Fletcher, D. F. Ingram, A. Aubin, J. Trujillo, W. Rosales Simmons, M. J. H. Univ Birmingham Sch Chem Engn Birmingham B15 2TT England Univ Toulouse Lab Genie Chim CNRS F-31400 Toulouse France Univ Sydney Sch Chem & Biomol Engn Sydney NSW 2006 Australia Unilever R&D Port Sunlight Lab Bebington CH63 3JW England

This study presents experimental data to identify transitional flow regime characteristics and assess state-of-theart turbulence models, specifically the Stress Blended Eddy Simulation (SBES), for predicting flow downstream of a square-edged orifice in a circular pipe using two Newtonian glycerol solutions with viscosities of 0.0054 and 0.0093 Pa s. Particle Image Velocimetry (PIV) and pressure drop measurements reveal distinct flow behaviours across regimes, with flow fields notably revealing dependence of regime transition boundaries on fluid viscosity for the same Reynolds number (Re). Maximum normalised velocity magnitude remains constant across all cases, but normalised velocity fluctuation at the orifice is halved for the high-viscosity fluid, indicating viscous damping. Self-similarity based on Re is observed in fully turbulent flows, while higher viscosity delays turbulence onset in the laminar and transitional regimes. This delay is influenced by viscosity and inlet velocity, affecting energy exchange and perturbation dissipation. The suitability of SBES is evaluated against Generalised k-omega (GEKO) and Wall Modelled Large Eddy Simulation (WMLES) turbulence models, as well as the laminar model. The laminar model is applicable only for true laminar flow, and the GEKO model fails to capture complex flow phenomena for both transitional and turbulent cases. Although SBES and WMLES models provide reasonably accurate predictions for high-Re flows, they incorrectly predict Re self-similarity in transitional cases. Discrepancies between SBES and WMLES predictions and experimental data highlight the inability of these models to fully capture the balance between viscous damping and vortex generation, especially for transitional regime flows in this orifice plate geometry.

关键词： CFD PIV transitional flow Instabilities Reynolds Scaling

来源：评论

学校读者我要写书评

暂无评论

Experimental investigation on transitional flow of supercritical hydrocarbon fuel within straight channels of Printed Circuit Heat Exchangers for hypersonic thermal management systems

引用

APPLIED THERMAL ENGINEERING 2025年 259卷

作者： Li, Jingqi Li, Yulong Xiayu, Tianyi Li, Xingjian Zheng, Rudao Beihang Univ Sch Energy & Power Engn Beijing 100191 Peoples R China Beihang Univ Natl Key Lab Sci & Technol Aero Engines Aerothermo Beijing 100191 Peoples R China Beihang Univ Collaborat Innovat Ctr Adv Aeroengine Beijing 100191 Peoples R China

The onboard supercritical CO2 closed Brayton cycle (SCBC) has established an effective thermal management pathway for hypersonic vehicles operating at high Mach numbers. A Printed Circuit Heat Exchanger (PCHE) is employed within the cycle system to facilitate heat transfer between fuel and carbon dioxide, with its thermohydraulic characteristics significantly impacting both power generation and propulsion performance. Given the insufficient research on the flow and heat transfer of hydrocarbon fuels in PCHEs, this study aims to experimentally address the gaps in understanding transition flow for supercritical hydrocarbon fuels, particularly within semi-circular microchannels. We conducted experiments on the flow transitions using a specially designed test piece with a diameter of 1 mm, replicating the PCHE channel characteristics. The experimental Reynolds number range from 300 to 8300 spans laminar, transition, and turbulent flow regimes. Friction factors for ndecane are obtained under adiabatic and heated conditions. The results validate the nomenclature of the quasiturbulent region and reveal that the critical Reynolds numbers for the transitional, quasi-turbulent and hydraulic smooth turbulent regions under adiabatic conditions are 2200, 2440 and 2980, respectively. A reduction in friction drag attributed to boundary layer viscosity is observed to alter the friction factor under heating conditions, while heating influences both the onset and termination of the transition region, but does not affect its width. Classical correlations are compared with the experimental results, and new empirical correlations for both adiabatic and non-adiabatic conditions are developed, showing superior predictive accuracy compared to existing models. This provides a reliable tool for the engineering design of heat exchangers in the onboard thermal manage systems.

关键词： Hypersonic Closed Brayton cycle Printed Circuit Heat Exchangers Hydrocarbon fuel transitional flow

来源：评论

学校读者我要写书评

暂无评论

transitional flow IN CHANNEL JUNCTIONS

引用

Journal of Hydrodynamics 2004年第4期16卷 464-467页

作者： NIHan-gen LIUYa-kun StateKeyLaboratoryofCoastalandOffshoreEngineering DalianUniversityofTechnologyDalian116024China

On the basis of energy and continuity equations a simple one-dimensionalformulation was proposed to predict the transitional flow at an open-channel junction. An empilicalrelation between the junction losses, the junction angle, and the discharge ratio was suggestedwhich agrees well with the experimental results. The results calculated by the present formulationfor the depth ratio were compared with the results of earlier one-dimensional formulations andexperiments. It is found that the present results coincide better with experiments than those ofothers.

关键词： open channel junctions energy losses transitional flow

来源：评论

学校读者我要写书评

暂无评论

transitional flow in the Venous Side of Patient-Specific Arteriovenous Fistulae for Hemodialysis

引用

ANNALS OF BIOMEDICAL ENGINEERING 2016年第8期44卷 2388-2401页

作者： Bozzetto, Michela Ene-Iordache, Bogdan Remuzzi, Andrea IRCCS Ist Ric Farmacol Mario Negri Dept Biomed Engn Via GB Camozzi 3 I-24020 Ranica BG Italy Univ Bergamo Dept Management Informat & Prod & Engn Viale Marconi 5 I-24044 Dalmine BG Italy

Arteriovenous fistula (AVF) is the first choice for providing vascular access for hemodialysis patients, but maintaining its patency is challenging. AVF failure is primarily due to development of neointimal hyperplasia (NH) and subsequent stenosis. Using idealized models of AVF we previously suggested that reciprocating hemodynamic wall shear is implicated in vessel stenosis. The aim of the present study was to investigate local hemodynamics in patient-specific side-to-end AVF. We reconstructed realistic geometrical models of four AVFs from magnetic resonance images acquired in a previous clinical study. High-resolution computational fluid dynamics simulations using patient-specific blood rheology and flow boundary conditions were performed. We then characterized the flow field and categorized disturbed flow areas by means of established hemodynamic wall parameters. In all AVF, either in upper or lower arm location, we consistently observed transitional laminar to turbulent-like flow developing in the juxta-anastomotic vein and damping towards the venous outflow, but not in the proximal artery. High-frequency fluctuations of the velocity vectors in these areas result in eddies that induce similar oscillations of wall shear stress vector. This condition may importantly impair the physiological response of endothelial cells to blood flow and be responsible for NH formation in newly created AVF.

关键词： Hemodialysis Vascular access Computational fluid dynamics transitional flow Wall shear stress Disturbed flow

来源：评论

学校读者我要写书评

暂无评论

transitional flow in intracranial aneurysms - A space and time refinement study below the Kolmogorov scales using Lattice Boltzmann Method

引用

COMPUTERS & FLUIDS 2016年 127卷 36-46页

作者： Jain, Kartik Roller, Sabine Mardal, Kent-Andre Univ Siegen Simulat Tech & Sci Comp Holderlinstr 3 D-57076 Siegen Germany Simula Res Lab Ctr Biomed Comp POB 134 N-1325 Lysaker Norway Univ Oslo Dept Math N-0316 Oslo Norway

Most Computational Fluid Dynamics (CFD) studies of hemodynamics in intracranial aneurysms are based on the assumption of laminar flow due to a relatively low (below 500) parent artery Reynolds number. A few studies have recently demonstrated the occurrence of transitional flow in aneurysms, but these studies employed special finite element schemes tailored to capture transitional nature of flow. In this study we investigate the occurrence of transition using a standard Lattice Boltzmann Method (LBM). The LBM is used because of its computational efficiency, which in the present study allowed us to perform simulations at a higher resolution than has been done in the context of aneurysms before. The high space-time resolutions of 8 mu m and 0.11 mu s resulted in nearly 1 x 10(9) cells and 9 x 10(6) time steps per second and allowed us to quantify the turbulent kinetic energy at resolutions that are of the order of the Kolmogorov scales. We perform an in-depth space and time refinement study on 2 aneurysms;one was previously reported laminar, while the other was reported transitional. Furthermore, we investigate the critical Reynolds number at which the flow transitions in aneurysms under time constant inflow conditions. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Intracranial aneurysm Lattice Boltzmann Method Convergence transitional flow

来源：评论

学校读者我要写书评

暂无评论

transitional flow In A Right-Angled Compound Open Canal Junction

引用

IRRIGATION AND DRAINAGE 2016年第1期65卷 73-84页

作者： Biswal, S. K. Mohapatra, P. K. Muralidhar, K. Natl Inst Technol Agartala Dept Civil Engn Tripura West 799055 India Indian Inst Technol Kanpur 208016 Uttar Pradesh India

Compound open canal junctions are of considerable importance in many engineering applications. This paper presents the details of the experimental procedure and the transitional flow characteristics over a partially rough bed in a right-angled canal junction. To record the instantaneous flow velocity, a 3D downward-facing acoustic Doppler velocimeter is used. A simplified mathematical model is employed to give a reasonable prediction of experimental results of a small portion of the data recorded. The hydraulics of flow at the canal junction, wherein the flow regime changes from subcritical to supercritical, is observed. The experimental results are presented in light of a dimensionless framework. The results reveal that the physical model describes the flow features well when there are changes in flow state from sub- to supercritical. Results of the present observation are compared with the available literature data. Being the first real study of transitional flow, the present work has provided valuable basic information about fundamental aspects of the hydrodynamics model. Copyright (c) 2016 John Wiley & Sons, Ltd.

关键词： compound canal junction transitional flow Froude number map stream traces head loss turbulence stress

来源：评论

学校读者我要写书评

暂无评论

transitional flow analysis in the carotid artery bifurcation by proper orthogonal decomposition and particle image velocimetry

引用

MEDICAL ENGINEERING & PHYSICS 2013年第7期35卷 898-909页

作者： Kefayati, Sarah Poepping, Tamie L. Univ Western Ontario Dept Phys & Astron London ON N6A 3K7 Canada Univ Western Ontario Dept Med Biophys Schulich Sch Med & Dent London ON N6A 3K7 Canada

Blood flow instabilities in the carotid artery bifurcation have been highly correlated to clot formation and mobilization resulting in ischemic stroke. In this work, Ply-measured flow velocities in normal and stenosed carotid artery bifurcation models were analyzed by means of proper orthogonal decomposition (POD). Through POD analysis, transition to more complex flow was visualized and quantified for increasing stenosis severity. While no evidence of transitional flow was seen in the normal model, the 50%-stenosed model started to show characteristics of transitional flow, which became highly evident in the 70% model, with greatest manifestation during the systolic phase of the cardiac cycle. By means of a model comparison, we demonstrate two quantitative measures of the flow complexity through the power-law decay slope of the energy spectrum and the global entropy. The more complex flow in the 70%-stenosed model showed a flatter slope of energy decay (-0.91 compared to -1.34 for 50% stenosis) and higher entropy values (0.26 compared to 0.17). Finally, the minimum temporal resolution required for POD analysis of carotid artery flow was found to be 100 Hz when determined through a more typical energy-mode convergence test, as compared to 400 Hz based on global entropy values. (c) 2012 IPEM. Published by Elsevier Ltd. All rights reserved.

关键词： Atherosclerotic plaque Blood flow velocity Entropy Carotid artery stenosis PIV POD Pulsatile flow transitional flow Turbulence

来源：评论

学校读者我要写书评

暂无评论

transitional flow in a Rushton Turbine Stirred Tank

引用

AICHE JOURNAL 2017年第8期63卷 3610-3623页

作者： Zhang, Yulong Gao, Zhengming Li, Zhipeng Derksen, J. J. Beijing Univ Chem Technol Beijing Adv Innovat Ctr Soft Matter Sci & Engn Beijing 100029 Peoples R China Beijing Univ Chem Technol Sch Chem Engn State Key Lab Chem Resource Engn Beijing 100029 Peoples R China Univ Aberdeen Sch Engn Aberdeen AB24 3UE Scotland

The way in which the single phase flow of Newtonian liquids in the vicinity of the impeller in a Rushton turbine stirred tank goes through a laminar-turbulent transition has been studied in detail experimentally (with Particle Image Velocimetry) as well as computationally. For Reynolds numbers equal to or higher than 6000, the average velocities and velocity fluctuation levels scale well with the impeller tip speed, that is, show Reynolds independent behavior. Surprising flow structures were measured-and confirmed through independent experimental repetitions-at Reynolds numbers around 1300. Upon reducing the Reynolds number from values in the fully turbulent regime, the trailing vortex system behind the impeller blades weakens with the upper vortex weakening much stronger than the lower vortex. Simulations with a variety of methods (direct numerical simulations, transitional turbulence modeling) and software implementations (ANSYS-Fluent commercial software, lattice-Boltzmann in-house software) have only partial success in representing the experimentally observed laminar-turbulent transition. (C) 2017 American Institute of Chemical Engineers

关键词： transitional flow stereoscopic particle image velocimetry computational fluid dynamics stirred tank Rushton turbine

来源：评论

学校读者我要写书评

暂无评论

transitional flow over an elliptic cone at Mach 8

引用

JOURNAL OF SPACECRAFT AND ROCKETS 2001年第6期38卷 941-945页

作者： Xiao, XD Edwards, JR Hassan, HA N Carolina State Univ Raleigh NC 27695 USA

The k-zeta transitional/turbulence model is used to study the transitional flow over an elliptic cone of aspect ratio of 2:1 at Mach 8 and a range of Reynolds numbers. Although the configuration has been the subject of detailed experimental and computational investigations, it has not been possible to determine with certainty the instability mechanisms responsible for transition. The present analysis suggests that none of the obvious mechanisms, i.e., second-mode or crossflow, are responsible for the transition. Instead, a form of bypass transition resulting from large-amplitude disturbances appears to reproduce quite well the experimentally measured heat-transfer data and the onset and the extent of transition over a wide range of Reynolds numbers.

关键词： transitional flow Mach Numbers Aspect Ratio Eddy Viscosity Angle of Attack Heat Transfer Boundary Layer Thickness Navier Stokes Equations Surface Roughness Turbulence Models

来源：评论

学校读者我要写书评

暂无评论

Effect of anisotropic resistance characteristic on boundary-layer transitional flow

引用

Applied Mathematics and Mechanics(English Edition) 2022年第12期43卷 1935-1950页

作者： Zheng HONG Zhengyin YE Kangling WU Kun YE National Key Laboratory of Science and Technology on Aerodynamic Design and Research Northwestern Polytechnical UniversityXi'an 710072China

It is observed that the feather surface exhibits anisotropic resistances for the streamwise and spanwise *** obtain a qualitative understanding about the effect of this anisotropic resistance feature of surface on the boundary-layer transitional flow over a flat plate,a simple phenomenological model for the anisotropic resistance is established in this *** means of the large eddy simulation(LES)with high-order accurate finite difference method,the numerical investigations are *** numerical results show that with the spanwise resistance hindering the formation of vortexes,the transition from laminar flow to turbulent flow can be delayed,and turbulence is weakened when the flow becomes fully turbulent,which leads to significant drag reduction for the *** the contrary,the streamwise resistance renders the flow less stable,which leads to the earlier transition and enhances turbulence in the turbulent region,causing a drag increase for the ***,it is indicated that a surface with large resistance for spanwise flow and small resistance for streamwise flow can achieve significant drag *** present results highlight the anisotropic resistance characteristic near the feather surface for drag reduction,and shed a light on the study of bird’s efficient flight.

关键词： anisotropic resistance transitional flow drag reduction numerical simulation

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：