Influence of Rheological Parameters on Turbulent Heat Transfer in Drag-Reducing Viscoelastic Channel Flow

2010 ◽  
Author(s):  
Takahiro Tsukahara ◽  
Takahiro Ishigami ◽  
Junya Kurano ◽  
Yasuo Kawaguchi
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Channel Flow ◽  
Reduction Rate ◽  
Turbulent Channel Flow ◽  
Weissenberg Number ◽  
Turbulent Heat Transfer ◽  
Rheological Parameters ◽  
Uniform Heat Flux ◽  
Turbulent Heat

Direct numerical simulations (DNS) of a drag-reducing viscoelastic turbulent channel flow with heat transfer had been carried out for three kinds of rheologically different fluids (e.g., different values of Weissenberg number). The molecular Prandtl number was set to be 0.1–2.0. A uniform heat-flux condition was employed as the thermal boundary condition. In this paper, we present various statistical turbulence quantities including the mean and fluctuating temperatures, the Nusselt number (Nu), and the cross-correlation coefficients and discuss about their dependence on the rheological parameters and the Prandtl-number dependency of the obtained drag-reduction rate and heat-transfer reduction rate.

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.

Heat transfer in a turbulent channel flow with square bars or circular rods on one wall

2015 ◽  
Vol 776 ◽  
pp. 512-530 ◽  
Author(s):  
S. Leonardi ◽  
P. Orlandi ◽  
L. Djenidi ◽  
R. A. Antonia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Prandtl Number ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Turbulent Heat ◽  
Turbulent Prandtl Number ◽  
Smooth Wall ◽  
Roughness Elements ◽  
Smooth Channel

Direct numerical simulations (DNS) are carried out to study the passive heat transport in a turbulent channel flow with either square bars or circular rods on one wall. Several values of the pitch (${\it\lambda}$) to height ($k$) ratio and two Reynolds numbers are considered. The roughness increases the heat transfer by inducing ejections at the leading edge of the roughness elements. The amounts of heat transfer and mixing depend on the separation between the roughness elements, an increase in heat transfer accompanying an increase in drag. The ratio of non-dimensional heat flux to the non-dimensional wall shear stress is higher for circular rods than square bars irrespectively of the pitch to height ratio. The turbulent heat flux varies within the cavities and is larger near the roughness elements. Both momentum and thermal eddy diffusivities increase relative to the smooth wall. For square cavities (${\it\lambda}/k=2$) the turbulent Prandtl number is smaller than for a smooth channel near the wall. As ${\it\lambda}/k$ increases, the turbulent Prandtl number increases up to a maximum of 2.5 at the crests plane of the square bars (${\it\lambda}/k=7.5$). With increasing distance from the wall, the differences with respect to the smooth wall vanish and at three roughness heights above the crests plane, the turbulent Prandtl number is essentially the same for smooth and rough walls.

Turbulent Heat Transfer in Plane Couette Flow

2004 ◽  
Author(s):  
Phuong M. Le ◽  
Dimitrios V. Papavassiliou
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Prandtl Number ◽  
Couette Flow ◽  
Channel Flow ◽  
Turbulent Dispersion ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Turbulence Structure ◽  
Plane Couette Flow

Direct numerical simulations of a turbulent plane Couette flow are combined with Lagrangian scalar tracking of thermal markers that are released in the flow field to determine the behavior of an instantaneous scalar line source located at the wall. The resulting probability density functions are used to calculate the behavior of instantaneous line sources of heat at the wall of the channel. The method is applied for fluids with a range of molecular Prandtl number, Pr, between 0.1 and 15,000, giving emphasis on the high Pr cases. The issues that are investigated are the effect of the Pr on turbulent dispersion, and the effect of the turbulence structure on turbulent heat transfer. The flow field for plane Couette flow is fundamentally different than that for channel flow, because the whole Couette flow domain is a constant stress region that forms an extensive logarithmic layer. For an instantaneous source at the wall, it is found that in both the channel flow and the Couette flow cases there are similar stages of development of the marker cloud that depend on the Prandtl number. This dependence becomes stronger as the Pr increases. However, this similarity is only qualitative.

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