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The effects of surface roughness on fully developed laminar and transitional flow friction factors and heat transfer coefficients in horizontal circular tubes

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2022年 189卷

作者： Everts, Marilize Robbertse, Pascal Spitholt, Blayne Univ Pretoria Dept Mech & Aeronaut Engn Pretoria South Africa

Although the effect of surface roughness on internal forced convection is considered a mature field, very limited work has been done focussing on the effect of surface roughness in the laminar and transitional flow regimes, especially for fully developed flow. Therefore, the purpose of this study was to experimentally investigate the simultaneous heat transfer and pressure drop characteristics in the laminar and transitional flow regimes for tubes with internally roughened surfaces. Experiments were performed using circular tubes with an internal diameter of 5.14 mm and a length of 5.45 m, with the smooth tube having a relative surface roughness close to 0, and the rough tubes having relative surface roughness values of 0.0 0 03 and 0.0 0 06. Water was used as the test fluid and the experiments were performed for Reynolds numbers between 500 and 9 800, while the Prandtl number varied between 4.32 and 7.01. Three different constant heat fluxes with values of 1, 2 and 3 kW/m(2) were applied to the test section while determining the friction factors from the pressure drop measurements and the heat transfer coefficients, Nusselt numbers and Colburn j-factors, from the measured fluid and surface temperatures. The Colburn j-factors and friction factors behaved similarly throughout the tested Reynolds range and the flow regime boundaries of the heat transfer and pressure drop results corresponded well. An increase in surface roughness favoured an increase in heat transfer in the laminar flow regime, but not in the other flow regimes. When investigating the influence of surface roughness on the critical Reynolds number, three distinct regions were identified and defined, namely, the Dampening region, Enhancing region and Saturating region. For low values of relative surface roughness, the onset of transition was delayed, while transition occurred earlier as the relative surface roughness was increased to moderate and high values. General trends in all three regions were tha

关键词： surface roughness heat transfer pressure drop transitional flow horizontal tubes

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Suspension of a single sphere in a stirred tank with transitional flow

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING 2023年第4期18卷

作者： Wang, Jianghao Huang, Fenglei Zhang, Kun Wang, Chao Li, Zhipeng Gao, Zhengming Derksen, Jos 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 China Natl Bluestar Grp Co Ltd Beijing 100029 Peoples R China Univ Aberdeen Sch Engn Aberdeen AB24 3UE Scotland

The lift-off characteristics of a single spherical particle in a stirred tank with transitional flow generated by a Rushton impeller have been explored in detail by using image capturing and processing techniques. We found three kinds of typical particle suspension motions, namely, the lightest PMMA particle first moves upward from the bottom center of the tank to a certain height and then spirals up to the impeller, the heavier POM particle rises to a certain height vertically and then it spirals down to the tank bottom, the still heavier PTFE and glass particles jump at random when they are rolling irregularly on the tank bottom. The single-phase flow field of the stirred tank was measured by using 2D-PIV technique to address the mechanism of the particle lift-off. The random distribution of the regions with larger liquid velocity closely above the tank bottom might be the reason why the PTFE and glass particles were lifted off randomly. As for the PMMA and POM particles being lifted from the bottom center and then stagnating at a certain height, the bulk flow dominates the particle suspension.

关键词： PIV solid-liquid suspension stirred tank transitional flow

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Curved-streamline transitional flow from mild to steep slopes

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JOURNAL OF HYDRAULIC RESEARCH 2009年第5期47卷 574-584页

作者： Castro-Orgaz, Oscar Hager, Willi H. Inst Agr Sostenible CSIC E-14080 Cordoba Spain ETH VAW CH-8092 Zurich Switzerland

flows from mild to steep slopes are relevant in hydraulic engineering relating to chute spillways and slope changes in irrigation networks. These flows are associated with transitional flow from sub-to super-critical conditions, smooth curvilinear-streamline feature involving a continuous free surface profile, and a rapid variation of the bottom pressure profile. Herein, the transition from a horizontal to a steeply sloping rectangular channel reach is investigated to analyze the application range of the Boussinesq-type equation. Slope breaks with a rounded transition from the brink section to the tailwater channel are considered and compared with the potential flow solution based on the Laplace equation. The Boussinesq-type equation is further compared with test data for a steep downstream slope to investigate the strong curvilinear gravity effect. A singular point analysis is also compared with the Boussinesq approach. The generalized momentum equation for curvilinear flows is developed and compared with the results pertaining to the energy concept.

关键词： Curvilinear flow One-dimensional flow Open channel Spillway transitional flow Weirs

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VERIFICATION OF APPLICABILITY OF THE TWO-EQUATION TURBULENCE MODELS FOR TEMPERATURE DISTRIBUTION IN transitional flow IN AN ELLIPTICAL TUBE

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THERMAL SCIENCE 2019年 23卷 S1113-S1121页

作者： Lopata, Stanislaw Oclon, Pawel Cracow Univ Technol Inst Thermal Power Engn Fac Mech Engn Krakow Poland

To increase the efficiency, elliptical tubes are often used in cross-flow heat exchangers. For these kinds of heat exchangers the flow field in the tubes exhibits irregularities. Therefore, various flow regimes can be observed: the turbulent, the transitional, and even the laminar one. Therefore, applying typical turbulence models for numerical calculations may cause significant errors, when flow in the heat exchanger tubes is in the transitional or laminar regime. Hence, the average values of flow velocities and temperature in heat exchanger tubes can be calculated incorrectly. The paper presents empirical verification of applying the basic two-equation turbulence models for a transitional flow of water in an elliptical pipe of a heat exchanger.

关键词： transitional flow heat transfer experimental investigation turbulence model

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A confrontation of 1D and 2D RKDG numerical simulation of transitional flow at open-channel junction

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INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS 2009年第7期61卷 752-767页

作者： Ghostine, R. Kesserwani, G. Mose, R. Vazquez, J. Ghenaim, A. Gregoire, C. ENGEES CNRS UMR 7507 UDSIMFS F-67000 Strasbourg France INSA Strasbourg F-67084 Strasbourg France ENGEES UMR 7517 LHYGES CNRSUDS F-67084 Strasbourg France

In this study. a comparison between the 1D and 2D numerical simulation of transitional flow in open-channel networks is presented and completely described allowing for a full comprehension of the modeling water flow. For flow in an open-channel network, mutual effects exist among the channel branches joining at a junction. Therefore, for the 1D study, the whole system (branches and junction) cannot be treated individually. The 1D Saint Venant equations calculating the flow in the branches are then supplemented by various equations used at the junction: a discharge flow conservation equation between the branches arriving and leaving the junction, and a momentum or energy conservation equation. The disadvantages of the 1D study are that the equations used at the junction are of empirical nature due to certain parameters Given by experimental results and moreover they often present a reduced field of validity. On the contrary, for the 2D Study, the entire network is considered as a single unit and the flow in all the branches and junctions is solved simultaneously. Therefore, we simply apply the 2D Saint Venant equations, which are solved by a second-order Runge-Kutta discontinuous Galerkin method. Finally, the experimental results obtained by Hager are used to validate and to compare the two approaches 1D and 2D. Copyright (C) 2009 John Wiley & Sons, Ltd.

关键词： open channel junctions Saint Venant equations discontinuous Galerkin method momentum conservation transitional flow steady flow

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Parallel Compatible Transition Closure Model for High-Speed transitional flow

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AIAA JOURNAL 2017年第9期55卷 3040-3050页

作者： Xu, Jiakuan Bai, Junqiang Fu, Ziyuan Qiao, Lei Zhang, Yang Xu, Jinglei Northwestern Polytech Univ Sch Aeronaut Xian 710072 Shaanxi Peoples R China Xi An Jiao Tong Univ Sch Aerosp Xian 701149 Shaanxi Peoples R China Beihang Univ Sch Energy & Power Engn Beijing 100191 Peoples R China

A single-point transition closure model that incorporates analytical results by stability theory in a reasonably wide range of Mach numbers has been formulated for supersonic/hypersonic boundary-layer flows, which includes two transport equations to specify the transition onset locations: one for the eddy-viscosity coefficient of laminar fluctuations and another for intermittency factor. The effects of compressibility are modeled through solutions of laminar self-similar boundary layer at subsonic and supersonic conditions with a totally local closure. Then, to form a complete transition turbulence model, the proposed transition model is coupled with the compressible k-omega shear stress transport turbulence model. In the end, several sets of well-documented flow cases are chosen to validate the present transition model, and the results are in satisfactory accord with experimental data. Proven by the numerical tests, the present model is capable of predicting well the supersonic/hypersonic transition onset that is dominated by the first and second Mack instability modes and laminar separation mode.

关键词： transitional flow Incompressible Boundary Layer Aerodynamic Configurations Kinematic Viscosity Turbulence Models Shear Stress Reynolds Averaged Navier Stokes Direct Numerical Simulation Compressibility Effect Turbulence Kinetic Energy

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Convective heat transfer and pressure drop characteristics of graphene-water nanofluids in transitional flow

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INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER 2021年 121卷

作者： Demirkir, Cayan Erturk, Hakan Bogazici Univ Dept Mech Engn TR-34342 Istanbul Turkey

The convective heat transfer and flow behavior of graphene-water nanofluids are studied experimentally by focusing on transitional flow. Graphene-water nanofluids with different particle mass fractions (0.025, 0.1 and 0.2%) are produced following two-step method and using PVP as a surfactant. Thermo-physical characterization is performed by measuring viscosity and thermal conductivity of the nanofluids. Convection characteristics are experimentally studied from laminar to turbulent flow regimes. It is seen that pressure drop increases dramatically in the transition region, and laminar to turbulent transition shifts to lower Reynolds numbers with increasing nanoparticle concentration. The transition initiates at a Reynolds number of 2475 for water, while it initiates at 2315 for the nanofluid with 0.2% particle mass fraction. Increase in mean heat transfer coefficient and Nusselt numbers are nearly identical at different Reynolds numbers and axial positions along the test tube in the laminar flow for nanofluids and water due to dominance of conduction enhancement mechanisms on the heat transfer increase in laminar flow. Beyond laminar flow regime, enhancement of Nusselt number is observed indicating that thermophoresis and Brownian motion are more effective heat transfer augmentation mechanisms. The maximum heat transfer enhancement is observed as 36% for a Reynolds number of 3950.

关键词： Nanofluid Graphene Convective heat transfer transitional flow Pressure drop Thermophoresis

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Fully Local Formulation of a Transition Closure Model for transitional flow Simulations

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AIAA JOURNAL 2016年第10期54卷 3015-3023页

作者： Xu, Jiakuan Bai, Junqiang Qiao, Lei Zhang, Yang Fu, Ziyuan Northwestern Polytech Univ Sch Aeronaut Xian 710072 Shaanxi Peoples R China

Anew computational fluid dynamics compatible transition model for the natural transition and laminar separation bubble induced transition is established using two transport equations with consideration of analysis results through linear stability theory linear stability theory. One transport equation is introduced to describe the growth of the laminar kinetic energy in the boundary layer. In addition, another transport equation of intermittency factor is built to trigger the transition by controlling the source term of turbulent kinetic energy equation. Finally, applying the two transport equations to a shear stress transport turbulence model completes a four-equation transition turbulence model. Comparisons of predictions using the new model with wind-tunnel experiments of the Schubauer and Klebanoff flat plate, S809 airfoil, Aerospatiale-A airfoil, and DLR-F5 wing validate the predictive qualities of the new transition turbulence model.

关键词： transitional flow Compressible Boundary Layer NACA 0036 Kinetic Energy Numerical Simulation Turbulence Models Shear Stress Wind Tunnels Kinematic Viscosity Reynolds Averaged Navier Stokes

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Numerical Simulation of transitional flow Past a Wing Using Flux Reconstruction Method

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AIAA JOURNAL 2016年第4期54卷 1424-1437页

作者： Skarolek, Vilem Miyaji, Koji Yokohama Natl Univ Grad Sch Environm & Informat Sci 79-5 Tokiwadai Yokohama Kanagawa 2408501 Japan Yokohama Natl Univ Dept Ocean & Space Syst Engn 79-5 Tokiwadai Yokohama Kanagawa 2408501 Japan

In this paper, the capabilities of a high-order flux reconstruction scheme for the implicit large-eddy simulations of a transitional flow at a low Reynolds number of 60,000 around the SD7003 wing are examined. This is the case posed in the First and Second International Workshops on the high-order computational fluid dynamics method held in 2012 and 2013. The correction function used in the flux reconstruction scheme is the Radau polynomial, which is equivalent to the discontinuous Galerkin scheme. A time-accurate implicit lower/upper symmetric Gauss-Seidel solution algorithm for the application of the flux reconstruction scheme to complex unsteady flows is developed, and it is found to be able to produce comparable results to the explicit Runge-Kutta scheme while achieving better computational efficiency. Simulations are carried out at alpha = 4 and 8 deg with polynomials of degree p = 1, 2, and 3 resulting in second-, third-, and fourth-order-accurate flux reconstruction schemes, respectively. Two structured hexahedral O-grid domains that differ in the grid resolution in a circumferential direction on the upper surface of the wing are considered, with a maximum of 2,000,000 degrees of freedom for the fourth-order (p = 3) simulations on the finer domain. The results are validated by comparison with many reference data obtained from various high-order schemes using time-accurate explicit/implicit methods. The results agree reasonably well. The developed method with the flux reconstruction scheme can be a reliable tool of implicit large-eddy simulations for low-Reynolds-number flows.

关键词： transitional flow Direct Numerical Simulation Freestream Mach Number Explicit and Implicit Methods Solution Algorithm Lift Coefficient Taylor Green Vortex Laminar Separation Bubble Skin Friction Coefficient Kelvin Helmholtz Instability

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Navier-Stokes airfoil computations with e^N transition prediction including transitional flow regions

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AIAA JOURNAL 2000年第11期38卷 2059-2066页

作者： Stock, HW Haase, W DLR German Aerosp Res Ctr Inst Design Aerodynam D-38108 Braunschweig Germany DaimlerChrysler Aerosp AG Flight Phys Dept Mil Aircraft Div D-81663 Munich Germany

The flow around laminar airfoils is computed using a Navier-Stokes method coupled to a transition prediction method based on the e(N) approach. Applying point transition at the predicted transition location produces a strong viscous/inviscid interaction region that prevents the coupled system from converging, whereas the introduction of transitional flow regions resolves that problem. The emphasis is not placed on the development of new transitional flow models but primarily on producing convergence, applying modified, available models. A comprehensive computational study is performed in a strong adverse and zero pressure gradient airfoil flow region, as the transitional lengths differ considerably for the different models. A conventional model, which is applicable in flow regions where transition is predicted well upstream of laminar separation, is proposed, together with a special transitional length model for flows where the boundary layer stays laminar up to separation. The flows over the DoAL3 and the NLF(1)-0416 laminar airfoils are investigated. The coupled Navier-Stokes and eN methods are shown to produce converged results. Furthermore, the values far lift and drag are in excellent agreement with the free transition measurements.

关键词： NLF(1) 0416 transitional flow Reynolds Averaged Navier Stokes Angle of Attack Laminar Turbulent Transition Low Turbulence Pressure Tunnel Skin Friction Freestream Mach Number Nacelles Compressibility

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