scholarly journals Role of large-scale coherent structures in impinging jet heat transfer.

1987 ◽  
Vol 20 (1) ◽  
pp. 71-76 ◽  
Author(s):  
KUNIO KATAOKA ◽  
RYUICHI SAHARA ◽  
HISASHI ASE ◽  
TAKAO HARADA
Keyword(s):  
Heat Transfer ◽  
Coherent Structures ◽  
Large Scale ◽  
Impinging Jet

Heat Transfer Characteristics of Baffled Channel Flow

2011 ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Large Scale ◽  
Heat Removal ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Heat ◽  
Two Parameters ◽  
Time Periodic

Heat transfer characteristics of baffled channel flow, where thin baffles are mounted on both channel walls periodically in the direction of the main flow, have been numerically investigated in a laminar range. In baffled channel flow, heat transfer characteristics are significantly affected by large-scale vortices generated due to flow separation at the tips of the baffles. In this investigation, a parametric study has been carried out to identify the optimal configuration of the baffles to achieve the most efficient heat removal from the channel walls. Two key parameters are considered, namely baffle interval (L) and Reynolds number (Re). We elucidate the role of the primary instability, a Hopf bifurcation from steady to a time-periodic flow, in the convective heat transfer in baffled channel flow. We also propose a contour diagram (“map”) of averaged Nusselt number on the channel walls as a function of the two parameters. The results shed light on understanding and controlling heat transfer mechanism in a finned heat exchanger, being quite beneficial to its design.

scholarly journals Heat and mass transfer enhancement strategies by impinging jets: A literature review

2020 ◽  
pp. 227-227
Author(s):  
Florin Bode ◽  
Claudiu Patrascu ◽  
Ilinca Nastase
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Large Scale ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Nozzle Geometry ◽  
Small Scale ◽  
Mixing Enhancement ◽  
Transfer Enhancement

Heat and mass transfer can be greatly increased when using impinging jets, regardless the application. The reason behind this is the complex behavior of the impinging jet flow which is leading to the generation of a multitude of flow phenomena, like: large-scale structures, small scale turbulent mixing, large curvature involving strong normal stresses and strong shear, stagnation, separation and re-attachment of the wall boundary layers, increased heat transfer at the impinged plate. All these phenomena listed above have highly unsteady nature and even though a lot of scientific studies have approached this subject, the impinging jet is not fully understood due to the difficulties of carrying out detailed experimental and numerically investigations. Nevertheless, for heat transfer enhancement in impinging jet applications, both passive and active strategies are employed. The effect of nozzle geometry and the impinging surface macrostructure modification are some of the most prominent passive strategies. On the other side, the most used active strategies utilize acoustical and mechanical oscillations in the exit plane of the flow, which in certain situations favors mixing enhancement. This is favored by the intensification of some instabilities and by the onset of large scale vortices with important levels of energy.

The role of large-scale coherent structures on screech amplitude

2001 ◽  
Author(s):  
Anjaneyulu Krothapalli ◽  
Mehmet Alkislar ◽  
Luiz Lourenco
Keyword(s):  
Coherent Structures ◽  
Large Scale

Convective Heat Transfer in Turbulent Flow Near a Gap

2006 ◽  
Vol 128 (7) ◽  
pp. 701-708 ◽  
Author(s):  
D. Chang ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Vortical Structures

Convective heat transfer in a rectangular duct containing a heated rod forming a narrow gap with a plane wall has been simulated by solving the unsteady Reynolds-averaged Navier-Stokes equations with a Reynolds stress model. Of particular interest is the role of quasi-periodic coherent structures in transporting fluid and heat across the gap region. It is shown that the local instantaneous velocity and temperature vary widely because of large-scale transport by coherent vortical structures forming in pairs on either side of the rod.

LES of a Round Impinging Jet: Investigation of the Link Between Nusselt Secondary Peak and Near-Wall Vortical Structures

2016 ◽  
Author(s):  
Pierre Aillaud ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Heat Transfer ◽  
Axial Velocity ◽  
Large Scale ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Secondary Peak ◽  
Wall Heat Transfer ◽  
Mixing Processes ◽  
Vortical Structures ◽  
The Mean

In an attempt to improve our understanding of the fundamental flow problem that is an impinging jet, a wall-resolved Large Eddy Simulation (LES) is produced to investigate large-scale unsteady flow features, mixing processes near the wall and heat transfer. The simulation focuses on a single unconfined round jet normally impinging on a flat plate at a Reynolds number (based on the pipe diameter and bulk velocity) of Re = 23 000 and for a nozzle to plate distance of H = 2D. This configuration is known to lead to a double peak in the Nusselt distribution. Evaluation of the high order statistics, such as Skewness and Kurtosis of the temporal evolution of axial velocity and wall heat flux, provides first-ever insights into the effect of the vortical structures on the mean wall heat transfer. Heat transfer statistics such as probability density functions (PDF) confirm the ability of LES to reproduce the strong intermittent thermal events responsible for the increase of the mean wall heat transfer radial distribution. Axial velocity and temperature temporal distributions are analysed simultaneously to gain further insight into the mixing process near the wall. In particular, the probabilities of the different cold/hot fluid ejection/injection events prove that the strong intermittent thermal events are linked to a change in the mixing behavior induced by the passage of the large-scale vortical structures. These structures are found to preferentially produce a cold fluid flux towards the wall leading to the local heat transfer enhancement usually identified by the secondary peak.

scholarly journals The role of large-scale vortical structures in transient convective heat transfer augmentation

2013 ◽  
Vol 718 ◽  
pp. 89-115 ◽  
Author(s):  
David O. Hubble ◽  
Pavlos P. Vlachos ◽  
Tom E. Diller
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Vortical Structure ◽  
Time Resolved ◽  
Vortical Structures ◽  
Heat Transfer Augmentation

AbstractThe physical mechanism by which large-scale vortical structures augment convective heat transfer is a fundamental problem of turbulent flows. To investigate this phenomenon, two separate experiments were performed using simultaneous heat transfer and flow field measurements to study the vortex–wall interaction. Individual vortices were identified and studied both as part of a turbulent stagnation flow and as isolated vortex rings impacting on a surface. By examining the temporal evolution of both the flow field and the resulting heat transfer, it was observed that the surface thermal transport was governed by the transient interaction of the vortical structure with the wall. The magnitude of the heat transfer augmentation was dependent on the instantaneous strength, size and position of the vortex relative to the boundary layer. Based on these observations, an analytical model was developed from first principles that predicts the time-resolved surface convection using the transient properties of the vortical structure during its interaction with the wall. The analytical model was then applied, first to the simplified vortex ring model and then to the more complex stagnation region experiments. In both cases, the model was able to accurately predict the time-resolved convection resulting from the vortex interactions with the wall. These results reveal the central role of large-scale turbulent structures in the augmentation of thermal transport and establish a simple model for quantitative predictions of transient heat transfer.

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