Evidence of flow vortex signatures on wall fluctuating temperature using unsteady infrared thermography for an acoustically forced impinging jet

Roux, Stéphane; Fénot, Matthieu; Lalizel, Gildas; Brizzi, Laurent-Emmanuel; Dorignac, Eva

doi:10.1016/j.ijheatfluidflow.2014.05.010

Cited by 13 publications

(8 citation statements)

References 30 publications

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“…The investigations of Vejrazka et al (2005), Buchlin (2011) and Roux et al (2011Roux et al ( , 2014 are in better agreement with the approach of Jambunathan et al (1992), suggesting a strong relationship between the large-scale vortical structures and the secondary maximum of Nu . 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).…”

Section: Heat Transfer At the Impingement Wallsupporting

confidence: 65%

“…The cold spots are elongated in the radial direction, leading to a filament propagation of the heat transfer (black arrows in figure 13b). This phenomenon has already been observed by Hadziabdic & Hanjalic (2008) and Roux et al (2014). In these previous studies, no link between the cold spots and a particular feature of the secondary vortices has been established.…”

Section: Large-scale Organisationmentioning

confidence: 63%

“…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. However, without synchronised velocity/temperature measurements, it is not possible to precisely link the vortex location to the increase or decrease in local heat transfer.…”

Section: Heat Transfer At the Impingement Wallmentioning

confidence: 99%

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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 Wallsupporting

confidence: 65%

Section: Large-scale Organisationmentioning

confidence: 63%

Section: Heat Transfer At the Impingement Wallmentioning

confidence: 99%

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

et al. 2015

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“…The first peak, which is located in the vicinity of the stagnation point, is believed to be caused by a strong acceleration of the fluid away from the center of the jet and with a flapping of the impingement position [14]. The secondary peak appears approximately two nozzle diameters away from the stagnation point, which is thought to be linked to large-scale vortical structures issuing from the jet shear layer [15]. Further, the influence of nozzle shapes on the heat transfer characteristic of impinging gas jets has been also investigated in various experimental studies, e.g., [16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Near-Wall Thermal Processes in an Inclined Impinging Jet: Analysis of Heat Transport and Entropy Generation Mechanisms

Ries

Klingenberg

et al. 2018

Energies

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In this work, near-wall thermal transport processes and entropy generation mechanisms in a turbulent jet impinging on a 45 ∘ -inclined heated surface are investigated using a direct numerical simulation (DNS). The objectives are to analyze the subtle mechanisms of heat transport in the vicinity of an inclined impinged wall, to determine the causes of irreversibilities that are responsible for the reduction of performance of impingement cooling applications and to provide a comprehensive dataset for model development and validation. Results for near-wall thermal characteristics including heat fluxes are analyzed. An entropy production map is provided from the second law analysis. The following main outcomes can be drawn from this study: (1) the location of peak heat transfer occurs not directly at the stagnation point; instead, it is slightly shifted towards the compression side of the jet, while at this region, the heat is transported counter to the temperature gradient; (2) turbulent thermal and fluid flow transport processes around the stagnation point are considerably different from those found in other near-wall-dominated flows and are strongly non-equilibrium in nature; (3) heat fluxes appear highly anisotropic especially in the vicinity of the impinged wall; (4) in particular, the heated wall acts as a strong source of irreversibility for both entropy production related to viscous dissipation and to heat conduction. All these findings imply that a careful design of the impinged plate is particularly important in order to use energy in such a thermal arrangement effectively. Finally, this study confirms that the estimation of the turbulent part of the entropy production based on turbulence dissipation rates in non-reacting, non-isothermal fluid flows represents a reliable approximate approach within the second law analysis, likewise in the context of computationally less expensive simulation techniques like RANS and/or LES.

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“…This certainly explains why the community has tried to understand the physical mechanisms affecting the wall heat transfer since the early detailed flow visualizations published by Popiel and Trass [8], highlighting the interaction between the well known vortical structures developing in a free jet and the impinged wall. A large number of studies focusing on the link between this unsteadiness present in impinging jet flows and the wall heat transfer can be found in the literature [9][10][11][12][13][14][15][16][17]. These basic studies, however, have mainly focused on the flat plate impingement.…”

Section: Introductionmentioning

confidence: 99%