纳秒等离子体激励控制翼型流动分离机理研究

为研究纳秒介质阻挡放电(NSDBD)等离子体控制翼型流动分离的物理机理,采用已建立的NSDBD唯象学模型耦合非定常Navier-Stokes方程模拟纳秒等离子体对流场的作用。使用非定常雷诺平均NavierStokes方程(URANS)和大涡模拟(LES)两种求解方法,研究纳秒等离子体激励对NACA0015翼型流动分离控制。结果表明:NSDBD等离子体激励促使边界层提前转捩,转捩对控制流动分离起重要作用;NSDBD激励开始时在翼型前缘形成展向涡,展向涡促使分离剪切层失稳并最终进入尾迹,展向涡贴近壁面运动,将外区的高能气流带入近壁区,使上翼面流场结构发生变化,然后翼型前缘流动提前转捩促使流动经过一个小层流分离泡后发生湍流再附,最终在上翼面形成稳定的附着流动。

Investigation on Mechanisms of Separation Control over an Airfoil Using Nanosecond Pulsed Plasma Actuator

A constructed one-zone inhomogeneous phenomenological model of Nanosecond Dielectric Barrier Discharge (NSDBD) is coupled with the unsteady Navier-Stokes equations to model the effects of nanosecond plasma actuation on flowfield. The coupled system is solved by using unsteady Reynolds-Averaged Navier-Stokes equations (URANS) which can predict the compression-expansion wave structures and wave speed well compared with experimental results and can be applied to simulate the flow control by using NSDBD. The model is adopted to investigate the separation control airfoil using NSDBD plasma actuator. The separation-control mechanisms over NACA0015 are investigated by using URANS and Large-Eddy Simulation (LES). It is found that the transition from laminar to turbulence can be promoted by plasma actuation, and that flow transition acts as an important factor in the flow-separation control. At the Begining of the actuation, each actuation can produce a spanwise vortex around the separation point near the leading edge. The spanwise vortices make the separated free-shear layer unstable and shedding away, move downstream along the upper wall, and bring outer flow with high kinetic energy into the near wall region to change the flow structures over the airfoil. Then, the flow around the leading edge of the airfoil reattach after encountering a separation bubble because of the earlier transition. At last, the flow on the upper surface of the airfoil become fully attached.