DNS of heat transfer in transitional, accelerated boundary layer flow over a flat plate affected by free-stream fluctuations

Wissink, Jan G.; Rodi, W.

doi:10.1016/j.ijheatfluidflow.2009.06.003

Cited by 4 publications

(3 citation statements)

References 17 publications

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“…Every case is simulated approximated for 15 flow-through times or 250 vortex shedding cycles. This shows that our simulation has been run for much longer time than the previous DNS studies (Wissink & Rodi 2006, 2009.…”

Section: Boundary Conditions and Computational Mesh Detailsmentioning

confidence: 86%

“…To the best of the authors' knowledge, only a handful of numerical studies are available in the literature on the subject of laminar heat transfer (Wissink & Rodi 2006, 2009Xiong & Lele 2007;Bhaskaran & Lele 2010;Wissink & Rodi 2011a,b;Venema et al 2011Venema et al , 2014. The studies of Xiong & Lele (2007) and Bhaskaran & Lele (2010) are large eddy simulations (LES), while the studies of Venema et al (2011Venema et al ( , 2014 are semi Direct Numerical Simulations (DNS), in the sense that the turbulence generating body is not fully resolved.…”

Section: Primary Factors Affecting Laminar Heat Transfermentioning

confidence: 99%

“…Numerical studies also have painted a better picture of this mechanism. For example, the DNS studies of Wissink & Rodi (2006), Wissink & Rodi (2009, 2011a showed that the increase in heat transfer occurs through an up-wash of hot fluid away from the cylinder and a down-wash of cold fluid towards the cylinder. The LES studies of Xiong & Lele (2007) and Bhaskaran & Lele (2010) observed longitudinal stream-wise vortical structures that increase heat transfer by being stretched along the surface of the turbine blade.…”

Section: Mechanism Of Heat Transfer Enhancementmentioning

confidence: 99%

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

2018

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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 11 %, while the peak location has the highest turbulence intensity of 15 %. 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 63 %, while in the decay region it is enhanced by only 28 %. 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.

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Section: Boundary Conditions and Computational Mesh Detailsmentioning

confidence: 86%

Section: Primary Factors Affecting Laminar Heat Transfermentioning

confidence: 99%

Section: Mechanism Of Heat Transfer Enhancementmentioning

confidence: 99%

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

2018

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Direct numerical simulation of heat transfer from the stagnation region of a heated cylinder affected by an impinging wake

Wissink

Rodi

2011

J. Fluid Mech.

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The effect of an incoming wake on the flow around and heat transfer from the stagnation region of a circular cylinder was studied using direct numerical simulations (DNSs). Four simulations were carried out at a Reynolds number (based on freestream velocity and cylinder diameter D) of Re D = 13 200: one two-dimensional (baseline) simulation and three three-dimensional simulations. The three-dimensional simulations comprised a baseline simulation with a uniform incoming velocity field, a simulation in which realistic wake data -generated in a separate precursor DNSwere introduced at the inflow plane and, finally, a simulation in which the turbulent fluctuations were removed from the incoming wake in order to study the effect of the mean velocity deficit on the heat transfer in the stagnation region. In the simulation with realistic wake data, the incoming wake still exhibited the characteristic meandering behaviour of a near-wake. When approaching the regions immediately above and below the stagnation line of the cylinder, the vortical structures from the wake were found to be significantly stretched by the strongly accelerating wall-parallel (circumferential) flow into elongated vortex tubes that became increasingly aligned with the direction of flow. As the elongated streamwise vortical structures impinge on the stagnation region, on one side they transport cool fluid towards the heated cylinder, while on the other side hot fluid is transported away from the cylinder towards the free stream, thereby increasing the heat transfer. The DNS results are compared with various semi-empirical correlations for predicting the augmentation of heat transfer due to free-stream turbulence.

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The logarithmic and power law behaviors of the accelerating, turbulent thermal boundary layer

Castillo

Hussain

2017

Physics of Fluids

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Direct numerical simulation of spatially evolving thermal turbulent boundary layers with strong favorable pressure gradient (FPG) shows that the thermal fluctuation intensity, θ′+ and the Reynolds shear stress, u′v′¯+ exhibit a logarithmic behavior spanning the meso-layer (e.g., 50≤y+≤170). However, the mean thermal profile is not logarithmic even in the zero pressure gradient (ZPG) region; instead, it follows a power law. The maxima of u′2¯+ and v′θ′¯+ change little with the strength of acceleration, while v′+, w′+, and u′v′¯+ continue to decay in the flow direction. Furthermore, θ′+ and u′θ′¯+ surprisingly experience changes from constants in ZPG to sharp rises in the FPG region. Such behavior appears to be due to squashing of the streaks which decreases the streak flank angle below the critical value for “transient growth” generation of streamwise vortices, shutting down production [W. Schoppa and F. Hussain, “Coherent structure generation near-wall turbulence,” J. Fluid Mech. 453, 57–108 (2002)]. The streamwise vortices near the wall, although shrink because of stretching, simultaneously, also become weaker as the structures are progressively pushed farther down to the more viscous region near the wall. While the vortical structures decay rapidly in accelerating flows, the thermal field does not—nullifying the myth that both the thermal and velocity fields are similar.

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DNS of heat transfer in transitional, accelerated boundary layer flow over a flat plate affected by free-stream fluctuations

Cited by 4 publications

References 17 publications

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

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

Direct numerical simulation of heat transfer from the stagnation region of a heated cylinder affected by an impinging wake

The logarithmic and power law behaviors of the accelerating, turbulent thermal boundary layer

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