Large Eddy Simulation Of Heat Transfer And Flow Characteristics Over Wavy Surfaces

The methods of heat transfer enhancement generally take vortex generators. However, increasing the heat transfer, it also makes flow resistance increased, so that the consumption of the pump power is increasing. The researches have shown that wavy wall flow characteristics are different from the conterpart of flat wall flows. The wavy surface could enhance the surface heat transfer. However, there are few reports of flow and heat transfer over wavy surfaces. The main objective here is to carry on with the investigation of the influence of different wavy surface on heat transfer and flow. Special attention will be given to the analysis of flow drag reduction and heat transfer enhancement over one wavy surface.Large eddy simulation has been employed to flow and heat transfer over solid wavy surface and flexible wavy surface for Re= 13800. The flexible wavy surface is obtained by imposed artificial fluctuation on the solid wavy surface, the vibrationfrequency of the flexible wavy surface is 10Hz.Computation of the solid wavy surface has been made for the five cases of different amplitude to wavelength ration of wall undulation: a / 0.01、0.02、0.03、0.04、0.05 . It is found that the smaller wave amplitude of wavy surface in this study does not form the recirculation in the valley. With increasing almplitude to a / =0.03, the flow separation is appeared in the valley. And the size of recirculation area becomes bigger owing to the earlier separation and the more delayed reattachment. A number of high wall sheer stress and Nusselt number spindle-shaped spots are observed in the up-slope part of the wavy surface. With increasing a / from 0.01 to 0.05,the time-averaged local Nusselt number and the non-dimensional pumping power Pp w are enhanced up to about 84.9% and 13.9%, respectively. And comprehensive coefficient increases the 0.6236. With increasing a / , comprehensive coefficient also increase evidently. It means that under the same pump power consumption , it is better for heat transfer with a bigger wave amplitude surface.A numerical investigation is conducted in a channel with one flexible wavy wall, Computation of the flexible wavy surface has been made for the four cases of different amplitude to wavelength ration of wall undulation: a / 0.01、0.02、0.03、0.04. A detailed analysis is carried out to investigate the pressure,velocity, temperature and so on for a / ? ? 0.03case.The results obtained indicate that periodic fluctuation of the wavy surface induces a periodic variation of pressure between favorable and adverse pressure gradients. It is also found that a number of high wall sheer stress and Nusselt number spindle-shaped spots are observed in the up-slope part of the wavy surface. Nusselt number and friction coefficient change periodically with time. This is different from solid wavy surface cases. With increasing a /? from 0.01 to 0.04,the time-averaged local Nusselt number and comprehensive coefficient show an increase of up to 173.1% and 1.0913, respectively. It means that the better heat transfer performance can be achieved with increasing flexible wall wave amplitude. The results show that flexible wavy wall with a big flexible wall amplitude could remarkably enhance heat transfer and reduce flow drag when compared to solid wavy surface with a same amplitude.