Investigation of the Flow Structure on a Flat Plate Induced by Unsteady Plasma Actuation with DNS Methods

An investigation into the flow characteristic on a flat plate induced by an unsteady plasma was conducted with the methods of direct numerical simulations（DNS）.A simplified model of dielectric barrier discharge（DBD） plasma was applied and its parameters were calibrated with the experimental results.In the simulations,effects of the actuation frequency on the flow were examined.The instantaneous flow parameters were also drawn to serve as a detailed study on the behavior when the plasma actuator was applied to the flow.The result shows that induced by the unsteady actuation,a series of vortex pairs which showed dipole formation and periodicity distribution were formed in the boundary layer.The production of these vortex pairs indicated a strong energy exchange between the main flow and the boundary layer.They moved downstream under the action of the free stream and decayed under the influence of the fluid viscosity.The distance of the neighboring vortices was found to be determined by the actuation frequency.Interaction of the neighboring vortices would be ignored when the actuation frequency was too small to make a difference.

Numerical analysis on phase change material melting process of a conical spiral tube energy storage tank

Spiral tube heat exchangers have been widely used in phase change energy storage due to the compact structure and large heat transfer area.Therefore,this study numerically analyzes the effects of spiral tube diameter,number of rotations,and unsteady heat source on the melting process in conical spiral tube energy storage tanks using Fluent software.The results indicate that when the tube diameter is increased from 8 to 11 mm and the number of rotations is increased from 5 to 8,the melting time is extended by 15.74%and 17.83%,respectively.The energy storage capacity increases by 0.64%and 1.83%,respectively.The average energy storage rate decreases by 13.05%and 13.58%,respectively.Furthermore,the sinusoidal wave heat source with small heat source periods has little effect on the melting process,while large heat source periods can significantly accelerate the melting.And the influence of amplitudes on the thermal storage performance under large heat source periods is more obvious.When the heat source period is increased from 2 to 160 min and the amplitude is increased from 5 to 20 K,the melting time is reduced by 24.50%and 17.20%,respectively.The total energy storage capacity decreases by 6.36%and increases by 1.62%,respectively.The average energy storage rate increases by 24.03%and 22.74%,respectively.The study provides guidance for the performance optimization of spiral tube phase change systems.