Oscillatory thermal structures induced by unconfined slot jet impingement

Narayanan, Vinod; Patil, Vishal

doi:10.1016/j.expthermflusci.2007.09.002

Cited by 7 publications

(2 citation statements)

References 17 publications

(31 reference statements)

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“…Very few experimental studies deal with the unsteady analysis of the temperature field in the impinging jet flow (see Narayanan & Patil 2007;O'Donovan & Murray 2007). In the work of Roux et al (2014), unsteady measurements of wall temperature for a round impinging jet at Re = 28 000 with H/D = 3 and 5 are performed, and the convection of successive cold and hot thermal fronts is clearly observed at the same frequency as the near-wall structures.…”

Section: Heat Transfer At the Impingement Wallmentioning

confidence: 98%

Direct numerical simulation of a turbulent jet impinging on a heated wall

et al. 2015

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Direct numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

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Section: Heat Transfer At the Impingement Wallmentioning

confidence: 98%

Direct numerical simulation of a turbulent jet impinging on a heated wall

et al. 2015

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“…From the results of many experiments and numerical simulations about the 2-dimensional impinging jet, it can also be seen that the plane impinging jet is unsteady flow and its symmetry is collapsed by the repeated formation and destruction of vortices in the upper and lower part of the plane jet at high Reynolds number. [9][10][11][12][13][14][15] The objective of the present study is to clarify the cause of the check-mark stain by scrutinizing in depth the numerical data obtained from numerical simulations of the unsteady compressible flow field which is formed when twodimensional plane gas jets collide with a moving vertical strip in a close distance. Studying the unsteady flow field obtained from numerical simulation results of our preceding researches, it was found that the flow field near the plane impinging jet ejected from the air-knife to the steel plate is not steady state but unsteady, and that large turbulent eddies change with time in a regular pattern.…”

Section: -7)mentioning

confidence: 99%

Aerodynamic Investigation about the Cause of Check-mark Stain on the Galvanized Steel Surface

2009

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Infrared thermography for convective heat transfer measurements

2010

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This paper deals with the evolution of infrared (IR) thermography into a powerful optical tool that can be used in complex fluid flows to either evaluate wall convective heat fluxes or investigate the surface flow field behavior. Measurement of convective heat fluxes must be performed by means of a thermal sensor, where temperatures have to be measured with proper transducers. By correctly choosing the thermal sensor, IR thermography can be successfully exploited to resolve convective heat flux distributions with both steady and transient techniques. When comparing it to standard transducers, the IR camera appears very valuable because it is non-intrusive, it has a high sensitivity (down to 20 mK), it has a low response time (down to 20 ls), it is fully two dimensional (from 80 k up to 1 M pixels, at 50 Hz) and, therefore, it allows for better evaluation of errors due to tangential conduction within the sensor. This paper analyses the capability of IR thermography to perform convective heat transfer measurements and surface visualizations in complex fluid flows. In particular, it includes the following: the necessary radiation theory background, a review of the main IR camera features, a description of the pertinent heat flux sensors, an analysis of the IR image processing methods and a report on some applications to complex fluid flows, ranging from natural convection to hypersonic regime.

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Oscillatory thermal structures induced by unconfined slot jet impingement

Cited by 7 publications

References 17 publications

Direct numerical simulation of a turbulent jet impinging on a heated wall

Direct numerical simulation of a turbulent jet impinging on a heated wall

Aerodynamic Investigation about the Cause of Check-mark Stain on the Galvanized Steel Surface

Infrared thermography for convective heat transfer measurements

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