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Communication Dans Un Congrès Année : 2018

Large eddy simulation of turbulent heat transfer in pipe flows of themally-dependent power-law fluids

Résumé

Heat transfer of turbulent forced convection of thermally-dependent power-law fluids, flowing in a heated horizontal pipe at isoflux conditions, is numerically analyzed by Large Eddy Simulations (LES), with an extended Smagorinsky model, at various Pearson numbers (0≤Pn≤5), for two power law indices (n=0.75 and 1), at Reynolds and Prandtl numbers Re=4000 and Pr=1. The apparent viscosity η of the non-newtonian fluid is modeled by η=Kγ^(n-1) , where n is the flow index and K=K°exp[Pn(θ-θ_b)], with K° the consistency at the bulk temperature, Pn=bT_ref the Pearson number, b the parameter of the therrmo-dependence and θ the dimensionless temperature. In the non-Newtonian Smagorinsky model, the turbulent viscosity accounts for the van Driest wall damping function and a correction function for the change in viscosity. This model was implemented in a finite difference laboratory code, with second-order space and time discretization schemes. The time advancement was based on a fractional step method. The grid size 65^3 was found to provide an accurate prediction of the turbulence statistics, in agreement with the literature data and to give a good compromise between the required CPU-time and accuracy. The LES predictions allow a better understanding of the physical mechanisms involved in the non-Newtonian thermally-dependent fluid flows: with increasing Pn, the viscosity is enhanced towards the pipe center, reducing the turbulent fluctuations and the turbulent heat transfer in the bulk. As a consequence, both the friction factor and Nusselt number are significantly reduced when Pn is large. The visualizations of the axial velocity fluctuations show a significant reduction of turbulence for the shear-thinning fluid (n=0.75) when Pn increases.
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Dates et versions

hal-02643473 , version 1 (04-06-2020)

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  • HAL Id : hal-02643473 , version 1

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Paulin Sourou Gnambode, Meryem Ould-Rouiss, Xavier Nicolas, Paolo Orlandi. Large eddy simulation of turbulent heat transfer in pipe flows of themally-dependent power-law fluids. 5th Internationnal conference on Turbulence and Interactions, Jun 2018, Trois-Ilets, Martinique, France. ⟨hal-02643473⟩
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