The Influence of Vortex Generators on the Drag and Heat Transfer From a Circular Cylinder Normal to an Airstream

1969 ◽  
Vol 91 (1) ◽  
pp. 91-99 ◽  
Author(s):  
T. R. Johnson ◽  
P. N. Joubert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Angular Position ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Experimental Investigations ◽  
Stagnation Line

Experimental investigations were carried out to examine the effect of vortex generators on drag and heat transfer from a circular cylinder in a crossflow. The cylinder was fitted with two rows of vortex generators which were symmetrically placed on either side of and parallel to the front stagnation line. One configuration of vortex generator was used and the angular position of the rows from the front stagnation line was varied. In the heat transfer runs the vortex generator position remained unvaried. Results are presented to show the variation of drag coefficient with Reynolds number for several angular positions of the generator rows. Results are also presented to show the variation of Nusselt number with Reynolds number both for a cylinder with and without generators. These show that both decreases in drag coefficient and increases in Nusselt number can be obtained when vortex generators are fitted.

Combined Influence of Fluid Viscoelasticity and Inertia on Forced Convection Heat Transfer From a Circular Cylinder

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
C. Sasmal ◽  
Mohd Bilal Khan ◽  
R. P. Chhabra
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Average Nusselt Number ◽  
A Priori ◽  
Convection Heat Transfer ◽  
Weissenberg Number ◽  
Elasticity Number

Abstract In this study, the combined influence of fluid viscoelasticity and inertia on the flow and heat transfer characteristics of a circular cylinder in the steady laminar flow regime have been studied numerically. The momentum and energy equations together with an appropriate viscoelastic constitutive equation have been solved numerically using the finite volume method over the following ranges of conditions: Reynolds number, 0.1≤Re≤20; elasticity number (= Wi/Re, where Wi is the Weissenberg number), 0≤El≤0.5; Prandtl number, 10≤Pr≤100 for Oldroyd-B and finitely extensible nonlinear elastic-Peterlin (FENE-P) (with two values of the chain extensibility parameter L2, namely 10 and 100) viscoelastic fluid models including the limiting case of Newtonian fluids (El = 0). New extensive results are presented and discussed in terms of the streamline and isotherm profiles, drag coefficient, distribution of the local and surface averaged Nusselt number. Within the range of conditions embraced here, the separation of boundary layers (momentum and thermal) is seen to be completely suppressed in an Oldroyd-B fluid whereas it is accelerated for a FENE-P fluid in comparison with that seen for a Newtonian fluid otherwise under identical conditions. At a fixed elasticity number, both the drag coefficient and average Nusselt number are seen to be independent of the Reynolds number beyond a critical value for an Oldroyd-B fluid. In contrast, the drag coefficient decreases and the average Nusselt number increases with Reynolds number for a FENE-P fluid at a constant value of the elasticity number. Finally, a simple correlation for the average Nusselt number for a FENE-P fluid is presented which facilitates the interpolation of the present results for the intermediate values of the governing parameters and/or its a priori estimation in a new application.

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

Fluid Flow and Heat Transfer Behavior for Turbulent Flows in a Tube With Vortex Generator Pairs for an Efficient Heat Exchanger

2018 ◽  
Author(s):  
Md. Islam ◽  
Z. Chong ◽  
S. Bojanampati
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Turbulent Flows ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Tube Diameter ◽  
Vortex Generators ◽  
Blockage Ratio ◽  
Delta Winglet

Various technologies have been developed to enhance flow mixing and heat transfer in order to develop an efficient compact heat exchanging devices. Vortex generators/turbulent promoters generate the vortices which reduce the boundary layer thickness and introduce the better mixing of the fluid to enhance the heat transfer. In this research experimental investigations have been carried out to study the effect of delta winglet vortex generator pairs on heat transfer and flow behavior. To generate longitudinal vortex flow, two pairs of the delta winglet vortex generators (DWVG) with the length of 10mm and winglet-pitch to tube-diameter ratio (PR = 4.8) are mounted on the inner wall of a circular tube. The DWVG pairs with two different winglet-height to tube-diameter ratios (Blockage ratio, BR = 0.1 and 0.2), three attack angles (α = 10°, 20°, 30°) and three spacings between leading edges (S = 10, 15 and 20mm) are studied. The experiments were conducted with DWVGs pairs for the air flow range of Reynolds numbers 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number and friction factor. The experimental results indicate that DWVG pair in a tube results in a considerable enhancement in Nusselt number (Nu) with some pressure penalty. It is found that DWVG increases Nu up to 85% over the smooth tube. It is also observed that Nusselt number increases with Re, blockage ratio and attack angle. Friction factor decreases with Re but increases with blockage ratio, spacing and attack angle. And 30° DWVG pair with S = 20mm, BR = 0.2 gets the highest friction factor. The Highest thermal performance enhancement (TPE) was noticed for α = 10°, S = 20mm, BR = 0.2 for turbulent flows. To obtain qualitative information on the flow behavior and vortex structures, flow was visualized by laser sheet using smoke as a tracer supplied at the entrance of the test section. The generation and development of longitudinal vortices influenced by DWVG pairs were clearly observed.

Impact of Delta-Winglet Pair of Vortex Generators on the Thermal and Hydraulic Performance of a Triangular Channel Using Al2O3–Water Nanofluid

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Hamdi E. Ahmed ◽  
M. Z. Yusoff
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Volume Fraction ◽  
Vortex Generator ◽  
Attack Angle ◽  
Vortex Generators ◽  
Triangular Channel ◽  
Delta Winglet ◽  
The Heat Transfer Coefficient

This paper presents the laminar forced convection of Al2O3–water nanofluid in a triangular channel, subjected to a constant and uniform heat flux at the slant walls, using delta-winglet pair (DWP) of vortex generator which is numerically investigated in three dimensions. The governing equations of mass, momentum, and energy are solved using the finite volume method (FVM). The nanofluid properties are estimated as constant and temperature-dependent properties. The nanoparticle concentrations and diameters are in ranges of 1–4% and 25–85 nm, respectively. Different attack angles of vortex generators are examined which are 7 deg, 15 deg, 30 deg, and 45 deg with range of Reynolds number from 100 to 2000. The results show that the heat transfer coefficient is remarkable dependent on the attack angle of vortex generators and the volume fraction of nanoparticles. The heat transfer coefficient increases as the attack angle increases from 7 deg to 30 deg and then diminishes at 45 deg. The heat transfer rate remarkably depends on the nanoparticle concentration and diameter, attack angle of vortex generator and Reynolds number. An increase in the shear stress is found when attack angle, volume fraction, and Reynolds number increase.

Performance Analysis for Elliptical Tube Longitudinal Vortex Generators

2011 ◽  
Vol 383-390 ◽  
pp. 6037-6041
Author(s):  
Jun Jie Zhou ◽  
Xue Hong Wu ◽  
Xiao Qian Li ◽  
Jin Yin Huang ◽  
Ding Biao Wang
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Coefficient ◽  
Vortex Generator ◽  
Heat Transfer Process ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Tube Heat Exchanger ◽  
Comprehensive Performance

In this paper, three-dimensional numerical simulation is conducted on the flow and heat transfer process for elliptical tube heat exchanger with rectangular vortex generators and triangular vortex generator by Fluent software, respectively, and the performance for elliptical tube heat exchanger with plate fin is compared. The results show that the Nusselt number increases with the increase in Reynolds number for the inlet velocity range from 1 to 5m/s, friction coefficient decreases with the increase in Reynolds number; at the same Reynolds number, Nusselt number for fin with Vortex Generators and friction coefficient are higher than that of elliptical tube with plate fin ; the vortex generator shape and angle of attack have a great impact on the comprehensive performance within a simulated attack angle and the velocity, at the same pump power, the comprehensive performance for heat exchanger with the rectangular vortex generator increase up to 10%.

scholarly journals Heat Transfer Enhancement and Flow Physics Behavior of Fluid in Circular Tube with Insert

2019 ◽  
Vol 8 (3) ◽  
pp. 1708-1715
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Leading Edge ◽  
Working Fluid ◽  
Literature Study

The paper presents computational fluid dynamics study of non-conventional insert vortex generator using Commercial software, to analyze the effect of vortex generator insert on heat transfer augmentation and fluid flow behavior. The study was done for Reynolds number 10000, 15000, 25000, 35000 and 45000 with working fluid as air flowing through a tube with a constant heat flux of 1000 w/m2. Current study validates the experimental results from the literature study. The heat transfer of these inserts with various geometrical arrangements viz. pitch to projected length ratio, angle of attack and height to inner diameter ratio are investigated here with the help of computational fluid dynamics software. The physical mechanism of formation and development of vortex flow from the leading edge to trailing edge of the insert is studied and it is observed that Nusselt number increases as an increment in Reynolds number. The ratio of augmented Nusselt number to smooth tube Nusselt number is found to be decreasing with increase in Reynolds number.

scholarly journals Heat transfer from a rotating circular cylinder in the steady regime: Effects of Prandtl number

2012 ◽  
Vol 16 (1) ◽  
pp. 79-91 ◽  
Author(s):  
Varun Sharma ◽  
Kumar Dhiman
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Circular Cylinder ◽  
Prandtl Number ◽  
Rotation Rate ◽  
Average Nusselt Number ◽  
Steady Regime ◽  
Rotating Circular Cylinder ◽  
Prandtl Numbers

In this work, effects of Prandtl number on the heat transfer characteristics of an unconfined rotating circular cylinder are investigated for varying rotation rate (? = 0 - 5) in the Reynolds number range 1 - 35 and Prandtl numbers range 0.7 - 100 in the steady flow regime. The numerical calculations are carried out by using a finite volume method based commercial CFD solver FLUENT. The isotherm patterns are presented for varying values of Prandtl number and rotation rate in the steady regime. The variation of the local and the average Nusselt numbers with Reynolds number, Prandtl number and rotation rate are presented for the above range of conditions. The average Nusselt number is found to decrease with increasing value of the rotation rate for the fixed value of the Reynolds and Prandtl numbers. With increasing value of the Prandtl number, the average Nusselt number increases for the fixed value of the rotation rate and the Reynolds number; however, the larger values of the Prandtl numbers show a large reduction in the value of the average Nusselt number with increasing rotation rate.

scholarly journals Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel With Cylindrical Vortex Generators

1996 ◽  
Author(s):  
Richard G. Hibbs ◽  
Sumanta Acharya ◽  
Yi Chen ◽  
Dimitris E. Nikitopoulos ◽  
Tod A. Myrum
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Transfer Rates ◽  
Average Mass ◽  
Side Walls

The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls: all four walls along each pass are active and have mass transfer from their surfaces but the ribs are non-participating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected inter-rib modules. Results are presented for Reynolds number in the range of 5,000 to 40,000. pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the inter-rib profiles along the ribbed walls more uniform. Along the side walls, horseshoe vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

scholarly journals Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel With Cylindrical Vortex Generators

1998 ◽  
Vol 120 (3) ◽  
pp. 589-600 ◽  
Author(s):  
R. G. Hibbs ◽  
S. Acharya ◽  
Y. Chen ◽  
D. E. Nikitopoulos ◽  
T. A. Myrum
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Transfer Rates ◽  
Average Mass ◽  
Side Walls

The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two-pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls; all four walls along each pass are active and have mass transfer from their surfaces but the ribs are nonparticipating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected interrib modules. Results are presented for Reynolds number in the range of 5000 to 40,000, pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise-averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the interrib profiles along the ribbed walls more uniform. Along the side walls, vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

scholarly journals Numerical Study on the Influence of Vortex Generator Arrangement on Heat Transfer Enhancement of Oil-Cooled Motor

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6870
Author(s):  
Junjie Zhao ◽  
Bin Zhang ◽  
Xiaoli Fu ◽  
Shenglin Yan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Vortex Generator ◽  
Attack Angle ◽  
Vortex Generators ◽  
Dimensionless Number ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Longitudinal Distance

At present, vortex generators have been extensively used in radiators to improve the overall heat transfer performance. However, there is no research on the effect of vortex generators on the ends of motor coils. Meanwhile, the current research mainly concentrates on the attack angle, shape and size, and lacks a detailed study on the transverse and longitudinal distance and arrangement of vortex generators. In this paper, the improved dimensionless number is used as the key index to evaluate the overall performance of enhanced heat transfer. Firstly, the influence of the attack angle on heat transfer enhancement is discussed through a single pair of rectangular vortex generators, and the results demonstrate that the vortex generator with a 45° attack angle is superior. On this basis, we compare the effects of different longitudinal distances (2 h, 4 h, and 6 h, h meaning the height of vortex generator) on enhanced heat transfer under four distribution modes: Flow-Up (FU), Flow-Down (FU), Flow-Up-Down (FUD), Flow-Down-UP (FDU). Thereafter, the performances of different transverse distances (0.25 h, 0.5 h, and 0.75 h) of the vortex generators are numerically simulated. When comparing the longitudinal distances, FD with a longitudinal distance of 4 h (FD-4h) performs well when the Reynolds number is less than 4000, and FU with a longitudinal distance of 4 h (FU-4h) performs better when the Reynolds number is greater than 4000. Similarly, in the comparison of transverse distances, FD-4h still performs well when the Reynolds number is less than 4000, and FU with a longitudinal distance of 4 h and transverse distance of 0.5 h (FU-4h − 0.5h) is more prominent when the Reynolds number is greater than 4000.

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