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Well-resolved direct numerical simulation (DNS) is applied to investigate strongly heated air flow in a vertical pipe ( L = 30 D ) at inlet Reynolds numbers of Re 0 = 4240 and 6020. The DNS is based on the experimental cases of Shehata and McEligot (1995) and shows excellent agreement with heat-transfer and flow statistical results. Flow relaminarization is observed in the strongly heated cases. We apply a new semi-local wall coordinate to replace the conventional one. With the semi-local wall coordinates, which considers the local property variation, both the velocity and temperature fields show the process of relaminarization. This relaminarization is also indicated by the significant decrease of turbulence intensity and Reynolds shear stress. In the quasi-laminar flow, the viscous sublayer becomes thicker. Turbulence in this layer shows a growing anisotropic character. And turbulence in the pipe center becomes approximately isotropic. This two-layer character is clearly displayed by flow visualization. [ABSTRACT FROM AUTHOR]

Numerical study is made of heat transfer enhancement in the narrow channel with insulated walls in air steady flow around a heated spherical dimple, when its relative depth is varied from 0 to 0.26 (in terms of spot diameter) at a defined Reynolds number 4 × 10 4 based on bulk velocity and dimple spot diameter. The applicability of multiblock computational technologies for solution of Reynolds and energy equations with the implication of an implicit factorized finite-volume algorithm and overlapping different-scale structured grids of different topology, as well as the verification of the shear stress transfer model (SST model) modified with regard to the streamline curvature within the framework of Leschziner–Rodi–Isaev’s approach is assessed from the comparison of numerical predictions obtained by different SSTM versions. Flow regimes in a spherical dimple, as its depth is increased, are classified on the basis of the analysis of change in the jet–vortex flow structure in the dimple and its wake in the channel. In what follows, special attention is paid to asymmetric flow around a dimple with the greatest vortex heat transfer enhancement. [ABSTRACT FROM AUTHOR]