Numerical Simulations of Turbulent Flume Heat Transfer at Pr = 5.4: Impact of the Smallest Temperature Scales

2005 ◽  
Author(s):  
R. Bergant ◽  
I. Tiselj
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Numerical Simulations ◽  
Passive Scalar ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Temperature Scales ◽  
Highly Correlated

In the present paper a role of the smallest diffusive scales of a passive scalar field in the near-wall turbulent flow was examined with pseudo-spectral numerical simulations. Temperature fields were analyzed at friction Reynolds number Reτ = 170.8 and at Prandtl number, Pr = 5.4. Results of direct numerical simulation (DNS) were compared with the under-resolved simulation where the velocity field was still resolved with the DNS accuracy, while a coarser grid was used to describe the temperature field. Since the smallest temperature scales remained unresolved in this simulation, an appropriate spectral turbulent thermal diffusivity was applied to avoid pileup at higher wave numbers. In spite of coarser numerical grid, the temperature field is still highly correlated with the DNS results, and thus point to practically negligible role of the diffusive temperature scales on the macroscopic behavior of the turbulent heat transfer.

DNS of Heat Transfer Reduction in Viscoelastic Turbulent Channel Flows

2015 ◽  
Author(s):  
Kyoungyoun Kim ◽  
Radhakrishna Sureshkumar
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Reduction Rate ◽  
Turbulent Channel Flow ◽  
Passive Scalar ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Uniform Heat Flux ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes

A direct numerical simulation (DNS) of viscoelastic turbulent channel flow with the FENE-P model was carried out to investigate turbulent heat transfer mechanism of polymer drag-reduced flows. The configuration was a fully-developed turbulent channel flow with uniform heat flux imposed on both walls. The temperature was considered as a passive scalar. The Reynolds number based on the friction velocity (uτ) and channel half height (δ) is 125 and Prandtl number is 5. Consistently with the previous experimental observations, the present DNS results show that the heat-transfer coefficient was reduced at a rate faster than the accompanying drag reduction rate. Statistical quantities such as root-mean-square temperature fluctuations and turbulent heat fluxes were obtained and compared with those of a Newtonian fluid flow. Budget terms of the turbulent heat fluxes were also presented.

Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pipe Flow ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Pitch Ratio ◽  
The Mean

In the current investigation, we performed large eddy simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow in order to study the effects of periodically mounted square ribs on heat transfer characteristics. The ribs were implemented on a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models were used to model Reynolds stresses and turbulent heat flux terms. A constant and uniform wall heat flux was imposed on all the solid boundaries. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number is fixed at Pr = 0.71. The blockage ratio (BR) based on the pipe diameter and rib height is fixed with 0.0625, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology, we focus on its effects on the characteristics of turbulent heat transfer. Mean flow and temperature fields are presented in the form of streamlines and contours. How the surface roughness, manifested by the wall-mounted ribs, affects the mean streamwise-velocity profile was investigated by comparing the roughness function. Local heat transfer distributions between two neighboring ribs were obtained for the pitch ratios under consideration. The flow structures related to heat transfer enhancement were identified. Friction factors and mean heat transfer enhancement factors were calculated from the mean flow and temperature fields, respectively. Furthermore, the friction and heat-transfer correlations currently available in the literature for turbulent pipe flow with surface roughness were revisited and evaluated with the LES data. A simple Nusselt number correlation is also proposed for turbulent heat transfer in ribbed pipe flow.

Turbulent Heat Transfer Enhancement in Round Tubes by Inserting Triple Twisted-Tapes

2015 ◽  
Author(s):  
S. Eiamsa-ard ◽  
P. Promthaisong ◽  
V. Chuwattanakul
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Flow Characteristics ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Round Tube ◽  
Constant Wall Temperature ◽  
Twisted Tapes ◽  
Twist Ratio

Turbulent flow characteristics and heat transfer performances in a round tube equipped with triple twisted tapes are investigated numerically. Effects of the triple twisted tapes at different twist ratios on the heat transfer and thermal performance characteristics are reported. The results of velocity and temperature fields, and the local heat transfer coefficients as well as the flow structure in tube with tape inserts are also given. A round tube wall is subjected to a constant wall temperature condition. Thermal field, heat transfer and fluid flow characteristics are studied using computational fluid dynamics (CFD) analysis. Computations, based on a finite volume method, are carried out by utilizing the Renormalized Group (RNG) k-ε turbulence model. The investigation is carried out for triple twisted tapes with y/W = 2.0, 3.0 and 4.0 in round tubes for laminar air flow with Reynolds numbers between 500 and 2000. It is found that the use of triple twisted tapes with smallest twist ratio of y/W = 2.0 results in the highest heat transfer and friction factor while the use of the tapes with the largest twist ratio (y/W = 4.0) results in the highest thermal performance. The highest thermal performances based on the constant pumping power criterion of the tubes equipped triple twisted tapes with y/W = 2.0, 3.0 and 4.0 are 2.43, 2.63 and 2.73, respectively.

Turbulent Heat Transfer Studies in Annulus With Inner Cylinder Rotation

1977 ◽  
Vol 99 (1) ◽  
pp. 12-19 ◽  
Author(s):  
T. M. Kuzay ◽  
C. J. Scott
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Annular Channel ◽  
Outer Wall ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Experimental Investigations ◽  
Turbulent Heat ◽  
Radial Temperature ◽  
Axial Temperature

Experimental investigations of turbulent heat transfer are made in a large-gap annulus with both rotating and nonrotating inner cylinder. The vertical annular channel has an electrically heated outer wall; the inner wall is thermally and electrically insulated. The axial air flow is allowed to develop before rotation and heating are imparted. The resulting temperature fields are investigated using thermocouple probes located near the channel exit. The wall heat flux, wall axial temperature development, and radial temperature profiles are measured. For each axial Reynolds number, three heat flux rates are used. Excellent correlation is established between rotational and nonrotational Nusselt number. The proper correlation parameter is a physical quantity characterizing the flow helix. This parameter is the inverse, of the ratio of axial travel of the flow helix in terms of hydraulic diameter, per half revolution of the spinning wall.

Direct Numerical Simulation of Condensing Stratified Flow

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Djamel Lakehal ◽  
Marco Fulgosi ◽  
George Yadigaroglu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Scaling Laws ◽  
Interfacial Shear Stress ◽  
Stratified Flow ◽  
Passive Scalar ◽  
Interfacial Shear ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat

The paper discusses the results of a detailed direct numerical simulation study of condensing stratified flow, involving a sheared steam-water interface under various thermal and turbulent conditions. The flow system comprises a superheated steam and subcooled water flowing in opposite directions. The transport equations for the two fluids are alternately solved in separate domains and then coupled at the interface by imposing mass, momentum, and energy jump conditions with phase change. The effects induced by changes in the interfacial shear were analyzed by comparing the relevant statistical flow properties. New scaling laws for the normalized heat transfer coefficient (HTC), K+, have been derived for both the steam and liquid phases. The steam-side law is found to compare with the passive-scalar law obtained hitherto by (Lakehal et al.(2003, “Direct Numerical Simulation of Turbulent Heat Transfer Across a Mobile, Sheared Gas-Liquid Interfaces,” ASME J. Heat Transfer, 125, pp. 1129–1139) in that HTC scales with Pr−3∕5. A close inspection of the transfer rates on the liquid side reveals a consistent relationship between K+, the local wave deformation or curvature and the interfacial shear stress. The surface divergence model of Banerjee et al. (2004, “Surface Divergence Models for Scalar Exchange Between Turbulent Streams,” Int. J. Multiphase Flow, 30(8), pp. 965–977) is found to apply in the liquid phase, too.

DNS of Turbulent Heat Transfer in Channel Flow With Heat Conduction in the Solid Wall

2001 ◽  
Vol 123 (5) ◽  
pp. 849-857 ◽  
Author(s):  
Iztok Tiselj ◽  
Robert Bergant ◽  
Borut Mavko ◽  
Ivan Bajsic´ ◽  
Gad Hetsroni
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Channel Flow ◽  
Temperature Fluctuations ◽  
Heat Fluxes ◽  
Wall Turbulence ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Fluid Temperature

The Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in the two-dimensional turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed at constant friction Reynolds number 150 and Prandtl numbers between 0.71 and 7 considering the fluid temperature as a passive scalar. The obtained statistical quantities like root-mean-square temperature fluctuations and turbulent heat fluxes were verified with existing DNS studies obtained with ideal thermal boundary conditions. Results of the present study were compared to the findings of Polyakov (1974), who made a similar study with linearization of the fluid equations in the viscous sublayer that allowed analytical approach and results of Kasagi et al. (1989), who performed similar calculation with deterministic near-wall turbulence model and numerical approach. The present DNS results pointed to the main weakness of the previous studies, which underestimated the values of the wall temperature fluctuations for the limiting cases of the ideal-isoflux boundary conditions. With the results of the present DNS it can be decided, which behavior has to be expected in a real fluid-solid system and which one of the limiting boundary conditions is valid for calculation, or whether more expensive conjugate heat transfer calculation is required.

Sign in / Sign up

Export Citation Format

Share Document