DNS Study of Turbulent Flow and Heat Transfer over Wavy Surfaces

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Abstract
Direct numerical simulation was performed for low Reynolds number turbulent flows over wavy surfaces and related heat transfer for the Prandtl number of 0.71. Geometric cases taken were the sine curve and its asymmetric deformations, i.e., wave crests shifted in upstream or downstream directions. Totally eight sets of geometrical parameters are tested for four steps of the wave amplitude (a/δ = 0, 0.025, 0.05, 0.10), but the mean pressure gradient driving the working fluid was kept constant through the simulations. The use of wavy surface resulted in remarkable enhancement of the bulk Nusselt number with deterioration of flow rate, and the pumping power saving was thus suggested. For the three patterns of wavy surfaces at a/δ = 0.1, values of the bulk Nusselt number are roughly four times as large as that of flat plate case consuming the same pumping power. Asymmetric deformation of wave affects the flow and thermal properties in a mild manner, but both upstream and downstream shifting of wave crests resulted in further heat transfer enhancement of 5 to 10 percent. Two-dimensional distributions of various turbulence statistics were presented, and detailed discussion was given to near wall phenomena causing the heat transfer enhancement.

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