In this paper,we present a direct numerical simulation(DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number(Re = 1) in a three-dimensional straight channel flow for the first time,using the Giesekus constitutive model for the fluid.In order to generate and maintain the turbulent fluid motion in the straight channel,a sinusoidal force term is added to the momentum equation,and then the elastic turbulence is numerically realized with an initialized chaotic velocity field and a stretched conformation field.Statistical and structural characteristics of the elastic turbulence therein are analyzed based on the detailed information obtained from the DNS.The fluid mixing enhancement effect of elastic turbulence is also demonstrated for the potential applications of this phenomenon.
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.
Actively cooled thermal protection system has great influence on the engine of a hypersonic vehicle, and it is significant to obtain the thermal and stress distribution in the system. So an analytic estimation and numerical modeling are performed in this paper to investigate the behavior of an actively cooled thermal protection system. The analytic estimation is based on the electric analogy method and finite element analysis(FEA) is applied to the numerical simulation. Temperature and stress distributions are obtained for the actively cooled channel walls with three kinds of nickel alloys with or with no thermal barrier coating(TBC). The temperature of the channel wall with coating has no obvious difference from the one with no coating, but the stress with coating on the channel wall is much smaller than that with no coating. Inconel X-750 has the best characteristics among the three Ni-based materials due to its higher thermal conductivity, lower elasticity module and greater allowable stress. Analytic estimation and numerical modeling results are compared with each other and a reasonable agreement is obtained.
Wang XinzhiHe YurongZheng YanMa JunjunH. Inaki Schlaberg
