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Effect of anisotropic resistance characteristic on boundary-layer transitional flow

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

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The experiment and analysis of transitional flow in pipe

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Journal of Hydrodynamics 2016年第2期28卷 313-318页

作者：王军杜广生王京盈耿介李冬 School of Energy and Power Engineering Shandong University Jinan 250061 China School of Thermal Engineering Shandong Jianzhu University Jinan 250101 China

The transitional flow in a pipe is important for delivery, but its characteristics remain to be explored. In this paper, the two-dimensional laser Doppler velocimetry （LDV） is used for the study, focusing on the attenuation characteristics of the axial velocity, the variation of the velocity gradient, the effect of the angle between the axis and the resultant velocity vector, and the relationship between the energy coefficient and the flow state. The attenuation characteristics of the axial velocity along the radial direction are obtained. It is shown that with the increase of the Reynolds number, the change rate of the velocity gradient slows down with a similar distribution, and a rapid decrease is seen in the near wall region. The amplitude and the frequency of the angular variation are obviously improved with the increase of the Reynolds number. The instability of the velocity field is enhanced with the increase of the energy coefficient.

关键词： transitional flow attenuation velocity gradient flow instability energy coefficient

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The effects of power law fluid rheology on coil heat transfer for agitated vessel in the transitional flow regime

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CANADIAN JOURNAL OF CHEMICAL ENGINEERING 2004年第6期82卷 1275-1283页

作者： Ricci, E Kelly, WJ Villanova Univ Dept Chem Engn Villanova PA 19085 USA

A CFD model of heat transfer from power-law fluids to helical cooling coils in the transitional flow regime of a baffled tank mixed with a pitched blade turbine was developed with Fluent (TM). The model captured local temperature and velocity gradients. Simulations were run, varying Re, Pr, K and n. The results indicate that a Sieder-Tate type correlation, with the exponent on and the coefficient in front of the Reynolds number being a function of n, is recommended for estimating ho. Also, a new two coil bank design was found to be more efficient when 450 < Re < 650.

关键词： pitched blade transitional flow power law fluids heat transfer coils

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Experimental Investigation of transitional flow in Porous Media with Usage of a Pore Doublet Model

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TRANSPORT IN POROUS MEDIA 2014年第2期101卷 333-348页

作者： Khayamyan, Shervin Lundstrom, T. Staffan Gustavsson, L. Hakan Lulea Univ Technol S-97187 Lulea Sweden

The transition from laminar to turbulent flow in porous media is studied with a new method. To mimic interconnected pores, a simplified geometry consisting of a pipe with a relatively large diameter that is split into two parallel pipes with different diameters is studied. This is a pore-doublet setup and the pressure drops over the parallel pipes are recorded by pressure transducers for different flow rates. Results show that the flow in the parallel pipes is redistributed when turbulent slugs pass through one of them. The presence of the slugs is revealed by positive skewness in the pressure signals as well as an increase of the standard deviation of the pressure drops and correlation between the pressure drops of the pipes. A frequency analysis of the pressure drops show that lower band frequency pressure variations in one pipe are communicated to the other pipe while higher band frequencies are filtered out.

关键词： Porous media transitional flow Turbulent flow Pore-doublet model Pipe flow

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Simulation of airfoil dynamic stall suppression with a burst control blade in a transitional flow regime

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JOURNAL OF THE BRAZILIAN SOCIETY OF MECHANICAL SCIENCES AND ENGINEERING 2022年第8期44卷 1-12页

作者： Salimipour, Erfan Yazdani, Shima Ghalambaz, Mehdi Quchan Univ Technol Dept Mech Engn Quchan Iran Duy Tan Univ Inst Res & Dev Da Nang 550000 Vietnam Duy Tan Univ Fac Elect Elect Engn Da Nang 550000 Vietnam

The present study numerically analyzed the effect of a passive flow control method to suppress the dynamic stall phenomenon on a NACA 0012 airfoil exposed to a uniform free flow at the transitional Reynolds number of 1.3 x 10(5). A thin blade was mounted on the airfoil's leading edge to control the separation bubble burst. The fluid relations of motion are the unsteady Reynolds-Averaged Navier-Stokes equations, solved implicitly by a second-order finite-volume solver. A three-equation transitional turbulence model with the capability of separation bubble prediction was used. Numerical results for several pressure distributions and aerodynamic coefficients were compared with available experimental results. The agreement was fair, confirming the reliability of the utilized computational method in the stall conditions. Results from the current work demonstrated that the control blade could prevent the separation bubble burst leading to a reduction in the static and dynamic stall effects. The blade caused a delay in the onset of the flow separation and improved the lift and drag coefficients, particularly in the pitch down motion of the airfoil. For the attack angle range between 5o and 15o, a significant dynamic stall control was observed, while at a wider range, the blade effect was low. The dynamic stall is a significant phenomenon resulting in a blade vibration due to the aeroelastic or hydrodynamic effects. The dynamic stall can lead to the flutter phenomenon that may cause the structure to break.

关键词： Numerical simulation transitional flow Dynamic stall Control blade Navier-Stokes equations

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PIV measurements and analysis of transitional flow in a reduced-scale model: Ventilation by a free plane jet with Coanda effect

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BUILDING AND ENVIRONMENT 2012年 56卷 301-313页

作者： van Hooff, T. Blocken, B. Defraeye, T. Carmeliet, J. van Heijst, G. J. F. Eindhoven Univ Technol Bldg Phys & Serv POB 513 NL-5600 MB Eindhoven Netherlands Katholieke Univ Leuven Div Bldg Phys B-3001 Louvain Belgium Katholieke Univ Leuven Dept Biosyst VCBT MeBioS B-3001 Louvain Belgium ETH Swiss Fed Inst Technol Zurich CH-8093 Zurich Switzerland Swiss Fed Labs Mat Testing & Res Empa Lab Bldg Sci & Technol CH-8600 Dubendorf Switzerland Eindhoven Univ Technol Fluid Dynam Lab NL-5600 MB Eindhoven Netherlands

Knowledge of indoor ventilation airflow is essential for creating a healthy, comfortable and energy-efficient indoor climate in buildings, airplanes, cars, ships, etc. In the past decades, numerical methods such as Computational Fluid Dynamics (CFD) have become primary tools to assess indoor airflow. However, validation of numerical simulations by high-quality experimental data is imperative. Although a lot of studies have focused on experimental data for turbulent ventilation flow, there is a lack of experimental data for transitional ventilation flow. transitional ventilation flow is in general associated with relatively low air velocities inside the enclosure. This paper presents detailed Particle Image Velocimetry (PIV) measurements and an analysis of transitional flow in a ventilated enclosure. The isothermal forced mixing ventilation flow is driven by a transitional plane jet. The measurements are performed in a reduced-scale water-filled model for slot Reynolds numbers ranging from 800 to 2500. flow visualizations indicate that this range of Reynolds numbers results in transitional flow, including the development of large coherent structures in the outer region of the jet. The measurements are analyzed in terms of mean velocity near the inlet and in the entire flow domain, and in terms of turbulence intensity and vorticity. Specific attention is given to the Coanda effect by which the free plane jet develops into a wall jet. The experimental data and analysis are specifically intended to support the development and validation of numerical models for ventilation flow. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： transitional flow Enclosed space Forced mixing ventilation Particle image velocimetry (PIV) Model validation Coanda effect

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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年第Sup4期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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Transition from turbulent to transitional flow in the top half of a stirred tank

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CHEMICAL ENGINEERING SCIENCE 2013年 98卷 218-230页

作者： Machado, Marcio B. Bittorf, Kevin J. Roussinova, Vesselina T. Kresta, Suzanne M. Univ Alberta Dept Chem & Mat Engn Edmonton AB T6G 2V4 Canada

The limits of fully developed turbulence are defined in the wall jet and in the recirculation flow for three different impeller geometries: A310, HE3 and PBTD. At two different tank scales, mean velocity profiles in both the wall jet and the recirculation flow were measured to determine whether the condition of fully turbulent self-similarity is satisfied. Higher impeller Reynolds numbers are able to keep the flow fully turbulent higher in the tank. In addition to the expected effect of impeller Reynolds number, the fluid also affected the flow regime. Measurements in a pilot scale stirred tank gave similar results. Although the power number is often constant for Re > 20 000, an impeller Re >= 300 000 is required to keep the flow in the fully turbulent regime in the top third of the tank and in the recirculation zone. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Stirred tank Mixing transitional flow Turbulence Wall jet Fully turbulent

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Numerical simulation on time-mean characteristics of flow and heat transfer of in line double-column cylinders in the transitional flow using compound grid system

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INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID 2017年 74卷 200-211页

作者： Zhou, Shaodong Xi, Guannan Shanghai Jiao Tong Univ 800 Dong Chuan Rd Minhang Dist Shanghai 200240 Peoples R China Nantong Univ 9 Se Yuan Rd Nantong 226019 Peoples R China

A computational model using a compound grid system for the in-line double column cylinders was developed to investigate the mechanisms of heat transfer enhancement in transitional flow. The results show that flow instability of wake flow causes two different effects, time-mean effect and statistical fluctuation effect (i.e. obtained from the time mean effect and the statistical fluctuation parameters, respectively), to enhance the heat transfer of the downstream cylinders. According to the clue, time-mean velocity and temperature in the wake of the upstream cylinders as the time-mean effect were investigated. It was found that fast recovery of velocity and temperature improves the effective Reynolds number and temperature difference. Then velocity cross-correction and velocity temperature cross-correction in the wake of the upstream cylinders as statistical fluctuation effect were investigated. It was found that the fluid mixing enhances the motion in a certain direction near the front face of cylinders. (C) 2016 Elsevier Ltd and IIR. All rights reserved.

关键词： Convection Heat transfer enhancement Heat exchanger Compound grid system transitional flow

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Analysis of transitional flow and heat transfer over turbine blades: algebraic versus low-Reynolds-number turbulence model

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 2001年第9期215卷 1003-1018页

作者： Sarkar, S Indian Inst Technol Dept Mech Engn Kanpur 208016 Uttar Pradesh India

The numerical simulation of flow and heat transfer over turbine blades involving laminar-turbulent transition is presented. The predicted results are compared with the experimental surface heat transfer and pressure distributions for two transonic turbine blades over a wide range of flow conditions. The time-dependent, mass-averaged Navier-Stokes equations are solved by an explicit four-stage Runge-Kutta scheme in the finite volume formulation. Local time stepping, variable-coefficient implicit residual smoothing and a full multigrid method have been implemented to accelerate the steady state calculation. The turbulence is simulated by the algebraic Baldwin-Lomax model together with an explicitly imposed model for transition. For comparison, the low-Reynolds-number version of the two-equation (k-epsilon) model of Chien is also used. The modified Baldwin-Lomax model performs well in predicting the onset of laminar-turbulent transition, whereas the Chien model shows a tendency to mimic the transition early and over a shorter distance.

关键词： Navier-Stokes analysis transitional flow turbine blade

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