Direct numerical simulation of heat transfer from a cylinder immersed in the production and decay regions of grid-element turbulence

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Title: Direct numerical simulation of heat transfer from a cylinder immersed in the production and decay regions of grid-element turbulence
Authors: Paul, I
Papadakis, G
Vassilicos, JC
Item Type: Journal Article
Abstract: The present direct numerical simulation (DNS) study, the first of its kind, explores the effect that the location of a cylinder, immersed in the turbulent wake of a grid-element, has on heat transfer. An insulated single square grid-element is used to generate the turbulent wake upstream of the heated circular cylinder. Due to fine-scale resolution requirements, the simulations are carried out for a low Reynolds number. Three locations downstream of the grid-element, inside the production, peak and decay regions, respectively, are considered. The turbulent flow in the production and peak regions is highly intermittent, non-Gaussian and inhomogeneous, while it is Gaussian, homogeneous and fully turbulent in the decay region. The turbulence intensities at the location of the cylinder in the production and decay regions are almost equal at 11Â %, while the peak location has the highest turbulence intensity of 15Â %. A baseline simulation of heat transfer from the cylinder without oncoming turbulence was also performed. Although the oncoming turbulent intensities are similar, the production region increases the stagnation point heat transfer by 63Â %, while in the decay region it is enhanced by only 28Â %. This difference cannot be explained only by the increased approaching velocity in the production region. The existing correlations for the stagnation point heat transfer coefficient are found invalid for the production and peak locations, while they are satisfied in the decay region. It is established that the flow in the production and peak regions is dominated by shedding events, in which the predominant vorticity component is in the azimuthal direction. This leads to increased heat transfer from the cylinder, even before vorticity is stretched by the accelerating boundary layer. The frequency of oncoming turbulence in production and peak cases also lies close to the range of frequencies that can penetrate the boundary layer developing on the cylinder, and therefore the latter is very responsive to the impinging disturbances. The highest Nusselt number along the circumference of the cylinder is shifted 45 degrees from the front stagnation point. This shift is due to the turbulence-generating grid-element bars that result in the prevalence of intense events at the point of maximum Nusselt number compared to the stagnation point.
Issue Date: 25-Jul-2018
Date of Acceptance: 10-Apr-2018
URI: http://hdl.handle.net/10044/1/66642
DOI: https://dx.doi.org/10.1017/jfm.2018.331
ISSN: 0022-1120
Start Page: 452
End Page: 488
Journal / Book Title: Journal of Fluid Mechanics
Volume: 847
Copyright Statement: © 2018 Cambridge University Press. This paper has been accepted for publication and will appear in a revised form, subsequent to peer-review and/or editorial input by Cambridge University Press.
Sponsor/Funder: Commission of the European Communities
Commission of the European Communities
Funder's Grant Number: 320560
FP7 - 317269
Keywords: Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
turbulence simulation
vortex interactions
wakes
FREE-STREAM-TURBULENCE
LOW-REYNOLDS-NUMBER
STAGNATION-REGION
BOUNDARY-LAYER
GENERATED TURBULENCE
VELOCITY-GRADIENTS
TURBINE CASCADE
FLOW
WAKES
INTERFACE
01 Mathematical Sciences
09 Engineering
Fluids & Plasmas
Publication Status: Published
Online Publication Date: 2018-05-23
Appears in Collections:Faculty of Engineering
Aeronautics



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