翼型绕流的洛伦兹力控制机理

在翼型上翼面壁面附近流场中形成的流向洛伦兹力,可提升翼型的升力减小阻力,然而制约其推广应用的主要瓶颈是极为低下的控制效率,为提高洛伦兹力的控制效率,需研究其控制机理.以翼型绕流的洛伦兹力控制为例,利用双时间步Roe格式及水槽对其进行数值及实验研究.结果表明:洛伦兹力的控制效果随着来流速度的增加而下降,升力增幅和阻力减幅与来流速度大小呈反比关系,但升力增加和阻力减小的规律不变,都是升力先急剧增加随后缓慢增加,而阻力先急剧减小然后再缓慢增加,基本原因为升力和阻力先受洛伦兹力推力的影响而分别增加和减小,随后洛伦兹力作用增加翼面壁面摩擦力,导致升力减小和阻力增加,流向洛伦兹力还导致翼型壁面压力下降,增加翼型升力和压差阻力;壁面摩擦力导致的升力降幅比壁面压力变化导致的升力增幅小,壁面压力变化起主导作用;洛伦兹力推力对阻力的降幅比压差阻力的增幅大,洛伦兹力推力起主导作用,因此阻力减小.

Control of flow around hydrofoil using the Lorentz force

The Lorentz force can be used to control the boundary layer flow of low-conduction fluids; however, its lowest control efficiency has become the main bottleneck in its engineering application. In order to enhance the control efficiency of Lorentz force, we need to study its potential control mechanism. In the present paper, the flow around hydrofoil when using Lorentz force has been simulated numerically by use of dual-time-step Roe method as well as studied experimentally in a water tank. Results show that the hydrofoil drag decreases sharply first and reincreases later, showing that the control effect of the Lorentz force is reduced with the increase of stream velocity, as well as the amplitude-change of the lift and drag; however, the lift increases continuously. The basic mechanism of this phenomenon is that the Lorentz force can form Lorentz force thrust, which increases the wall friction and decreases the pressure on the hydrofoil surface; at the incipient stage of control, the Lorentz force thrust decreases the drag and increases the lift immensely, soon afterwards, due to the action of Lorentz force, the drag increases with the increase of wall shear force and the lift increases with the decrease of upper surface pressure, so that the thrust can increase both the drag and lift.