Heat Transfer in Separated Flow behind a Circular Cylinder for Reynolds Numbers from 120 to 30000 (2nd Report, Unsteady and Three-Dimensional Characteristics) (original) (raw)
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Unsteady heat transfer from a circular cylinder for Reynolds numbers from 3000 to 15,000
International Journal of Heat and Fluid Flow, 2004
Unsteady heat transfer from a circular cylinder to the cross-flow of air was investigated experimentally for Reynolds numbers from 3000 to 15000. Fluctuating heat transfer on the cylinder surface was measured using a heat flux sensor, and time-spatial characteristics of the heat transfer were measured using an infrared thermograph. The present measurements showed that the alternating rolling-up of the shear layers that separated from the cylinder forms an alternating reattached flow at the rear of the cylinder in the range of Re > 5000 -8000, due to the forward movement of the vortex formation region with increasing Reynolds number. This leads to a sharp increase in the time-averaged Nusselt number around the rear stagnation point of the cylinder. The heat transfer in the separated flow region has spanwise nonuniformity throughout the examined Reynolds number range. The wavelength of this nonuniformity corresponds to that of the streamwise vortices formed in the near-wake.
Heat transfer from a cylinder in the wake flow
International Communications in Heat and Mass Transfer, 2000
In this experimental study, heat transfer from a circular cylinder placed behind an obstacle in cross-flow was investigated. In the experiments two types of cylindrical obstacles, one with circular cross-section and the other with square cross-section, were used in order to test the effect of geometrical shape of the obstacle on heat transfer from the test cylinder. In addition, the effects of obstacle size and the separation between the obstacle and the test cylinder were investigated in the interval of Reynolds numbers 1,100 < Re < 19,500 and for the dimensionless separation ratios ranging from 0.8 to 9. Based on the measurements, average Nusselt number was determined using lumped heat capacitance method. From the results, it is observed that the shape and size of the obstacle significantly affect the heat transfer from a cylinder in the wake flow region.
Analysis of low Reynolds number flow around a heated circular cylinder
Journal of Mechanical Science and Technology, 2009
The objective of this study is to investigate the forced convection from and the flow around a heated cylinder. Experimental and computational results are presented for laminar flow around a heated circular cylinder with a diameter of 10 mm. The experiments were carried out using Particle Image Velocimetry (PIV) in a wind tunnel, and numerical simulations using an in-house code and a commercial software package, FLUENT. This paper presents comparisons for vorticity and temperature contours in the wake of the cylinder. Experimental and computational results are compared with those available in the literature for heated and unheated cylinders. An equation is suggested for a temperature-dependent coefficient defining a reference temperature to be used in place of the constant used in other studies. An attempt is also made to correct differences between average cylinder surface temperature and measured interior temperature of the cylinder.
STUDY OF TURBULENT FLOW DOWNSTREAM FROM A LINEAR SOURCE OF HEAT PLACED INSIDE THE CYLINDER WAKE
iaeme
A turbulent flow downstream from a linear source of heat placed inside the cylinder wake has been studied numerically in this paper. Special attention has been paid to the cylinder wake effect on the source of heat diffusion in downstream flow. The turbulent model has been applied a standard - two equations model and the two-dimensional Reynolds Averaged Navier–Stokes (RANS) equations are discretized with the second order upwind scheme. The SIMPLE algorithm, which is developed using control volumes, is adopted as the numerical procedure. Calculations were performed for a wide variation of the Reynolds numbers. The investigations reveal that with increasing Reynolds number, the instabilities appear in the wake zone, showing an oscillatory flow, also called von Karman Vortex Street. His geometry has an important influence on the thermal field and the diffusion process. Comparison of numerical results with the experimental data available in the literature is satisfactory.
International Journal of Heat and Mass Transfer, 2014
In this paper, a numerical investigation is performed to study the mixed convective flow and heat transfer characteristics past a square cylinder in cross flow at incidence. Utilizing air (Pr = 0.71) as an operating fluid, computations are carried out at a representative Reynolds number (Re) of 100. Angles of incidences are varied as, 0°6 a 6 45°. Effect of superimposed positive and negative cross-flow buoyancy is brought about by varying the Richardson number (Ri) in the range À1.0 6 Ri 6 1.0. The detail features of flow topology and heat transport are analyzed critically for different angles of incidences. The thermo fluidic forces acting on the cylinder during mixed convection are captured in terms of the drag (C D), lift (C L), and moment (C M) coefficients. The results show that the lateral width of the cylinder wake reduces with increasing a and the isotherms spread out far wide. In the range 0°< a < 45°, C D reduces with increasing Ri. The functional dependence of C M with Ri reveals a linear relationship. Thermal boundary layer thickness reduces with increasing angle of incidences. The global rate of heat transfer from the cylinder increases with increasing a.
Analysis of flow around a heated circular cylinder
2008
The objective of this study is to investigate the forced convection from and the flow around a heated cylinder. Experimental and computational results are presented for laminar flow around a heated circular cylinder with a diameter of 10 mm. The experiments were carried out using Particle Image Velocimetry (PIV) in a wind tunnel, and numerical simulations using an in-house code and a commercial software package, FLUENT. This paper presents comparisons for vorticity and temperature contours in the wake of the cylinder. Experimental and computational results are compared with those available in the literature for heated and unheated cylinders. An equation is suggested for a temperature-dependent coefficient defining a reference temperature to be used in place of the constant used in other studies. An attempt is also made to correct differences between average cylinder surface temperature and measured interior temperature of the cylinder.
2016
Considerable attention has been given to flows passing over bluff bodies such as cylinders. This is due to their importance in applications such as heat exchanger, cooling towers and electronic circuit cooling. It has been proved that flow performance and heat transfer could be improved remarkably if the cylinders rotate and flow stabilizers/blockers are used to increase residence time and Nusselt number. This is due to the effect of the vortical structures in the wake region on the drag and heat transfer coefficients. Therefore, forced convection heat transfer across stationary and rotating horizontal cylinder dissipating uniform heat flux was investigated numerically and experimentally in this work. The maximum values of rotational and crossflow Reynolds numbers attained were 960 and 160, respectively. The non-dimensional rotational velocity (α) was varied from 0 to 6. Finite volume numerical simulations using ANSYS were performed. Average temperatures of the cylinder surface were measured by using a thermal camera and the flow profile was captured by High Speed Photography and LDV, offering new experimental results for correlation purposes. Results show that the maximum average heat transfer rate occurs at the same Reynolds number whilst the minimum value occurs at the higher rotational Reynolds number. At higher rotational Reynolds numbers the Nusselt number is nearly independent of Reynolds number and thermal boundary conditions. Comparison with previous numerical studies showed good agreement.
The present work is an initiative towards improving heat transfer and reducing drag for the case of flow past cylinder by utilizing triangular wake splitter. Flow past circular cylinder and cylinder with triangular and rectangular wake splitter has been studied for low Reynolds number 5, 20, 40, 50, 60, 80, 100,200. Flow and thermal analyses were performed for the case of constant wall temperature. Length of wake splitter in both configurations is taken to be equal to diameter of cylinder. Fluent 6.2.16 is used for the purpose of analysis. An incompressible SIMPLEC finite volume code employing a non-staggered grid arrangement is used. Second order upwind scheme is used for convective terms. Time discretization is implicit and a Second order Crank-Nicholson scheme is employed. Effect of wake splitter on wake formation, vortex generation, Nusselt number, heat transfer has been numerically studied and variations have been plotted. Validation has been carried out for average Nusselt number on single cylinder for Reynolds number 200 and results were found to be in good agreement with available experimental and numerical work. Heat transfer with drag coefficient 8% lower compared to bare cylinder. Performance of triangular wake splitter has been found to be similar to rectangular wake splitter. Results point triangular wake splitter has been found to be 17% more and towards cylinder with triangular wake splitter being more efficient than other configurations.
Flow over and forced convection heat transfer around a semi-circular cylinder at incidence
International Journal of Heat and Mass Transfer, 2012
Wake dynamics and forced convective heat transfer characteristics past a semi-circular cylinder at incidence have been investigated numerically. Utilizing air as an operating fluid computations are carried out for wide ranges of the Reynolds number (80 6 Re 6 180) and angle of incidences (0 6 a 6 180°). Angle of incidence reveals three flow separation zones. Structure properties of shear layer and vortex motions on each flow separation zones are analyzed critically. Functional dependence of drag (C D), lift (C L), and moment (C M) coefficients on the angle of incidence is explored and analyzed in detail. Increase in angle of incidence increases streamline curvature. A structural similarity is observed between the contours of vorticity and the corresponding isotherms. Strouhal number shows a decreasing trend up to certain values of a and thereafter it increases marginally. A new correlation of Strouhal number as a function of Re and a has been established for the present range of Reynolds numbers. At the singularity points a sudden jump in local Nusselt number distribution is observed. The trend of variation of average Nusselt number with a is similar to that of Strouhal number variation. The average Nusselt number is found to vary as Re 0:529 ð1 þ aÞ À0:0476 .