Kazuaki Sugawara

DNS of Three-Dimensional Unsteady Separated Flow and Heat Transfer Around a Downward Step

The direct numerical simulation methodology was employed to analyze the unsteady features of a three-dimensional separated flow and heat transfer around a downward step in a rectangular channel. Numerical calculations were carried out using the finite difference method. The Reynolds number Re based on the mean velocity at inlet and the step height was varied from 300 to 1000. The channel expansion ratio ER is 2.0 under a step aspect ratio of 36.0. It is found that the flow is steady upto Re = 500, but becomes sensibly unsteady at Re = 600 as accompanying a remarkable increase of the three-dimensionality of the flow and temperature fields. Nusselt number reaches its maximum in the reattachment flow region and also in the neighborhood of the side wall, and their locations depend greatly upon Re.Copyright

DNS of Expansion Ratio Effects on Three-Dimensional Unsteady Separated Flow and Heat Transfer Around a Downward Step

The direct numerical simulation methodology was employed to analyze the unsteady features of a three-dimensional separated flow and heat transfer around a downward step in a rectangular channel, and to clarify systematically the channel expansion ratio effects upon them. Numerical calculations were carried out using the finite difference method. The Reynolds number Re based on the mean velocity at inlet and the step height was varied from 300 to 1000. The channel expansion ratio ER is 1.5, 2.0 and 3.0 under a step aspect ratio of 36.0. It is found that the flow is steady upto Re = 500 but becomes sensibly unsteady at Re = 700 for all the three expansion ratios. In the case of ER = 2.0, the separated shear layer is most unstable. In the case of ER = 1.5, the longitudinal vortices formed near the side walls of channel are strongest. Nusselt number reaches its maximum in the reattachment flow region and also in the neighborhood of the side wall, and their locations depend greatly upon ER and Re.Copyright

LES of Turbulent Separated Flow and Heat Transfer in a Symmetric Expansion Plane Channel

LES method is applied to simulate numerically a turbulent separated and reattached flow and heat transfer in a symmetric expansion plane channel of expansion ratio 2.0. Smagorinsky model is used in the analysis and fundamental equations are discretized by means of the finite difference method, and their resulting finite difference equations are solved using SMAC method. The calculations are conducted for Re = 15000. It is found that the present numerical results, in general, agree well with the previous experimental ones. The complicated vortical flow structures in the channel and their correlations with heat transfer characteristics are visualized through various fields of flow quantities.Copyright