电磁力作用下绕流减阻与优化控制

Drag Reduction and Optimal Control of Cylinder Wake Via Lorentz Force

电介质溶液中,电磁场产生的Lorentz力可以控制流体的运动。将其用于钝体绕流时,可以减少阻力、抑制分离和消除涡街。为了使这种控制更加经济和有效,电磁场的强度即控制强度,应当是优化的,随流场实时调正的。基于优化控制理论,以圆柱绕流的电磁优化控制为例,推导了流场电磁控制的性能指标表达式和协态方程,并对雷诺数Re为200流场的非线性优化控制问题进行了数值研究,流场的基本方程为指数极坐标中考虑场力的Navier-Stokes方程,计算采用交替方向隐式格式和快速傅里叶变换格式。得到了优化电磁场强度的变化规律,讨论了该优化控制下,流场和圆柱表面阻力和升力的变化过程。研究结果表明,通过优化控制,可以达到减少阻力、抑制分离和消除涡街及涡生振荡的目的。

The flow of the weak electrolyte solution can be controlled by Lorentz forces generated by the suitably chosen magnetic and electric fields,which can be used for the drag reduction,the suppression of vortex shedding and the vortex street in the flow over a bluff body.In order to get a large control effect with small power input,the interaction parameter N,the ratio of the electromagnetic force to the inertia force serving as control input in the control process,should be optimized according to the instantaneous flow field.An adjoint-based ensemble optimization method of control algorithms was developed via Lorentz forces.The performance index and adjoint equations in the expolential-polar coordinates were derived.Numerical simulations based on the Navier-Stokes equations and its adjoint equations for optimal control of cylinder wake were carried out for Reynolds number Re=200.Based on the Navier-Stokes equations considering the electromagnetic body force,i.e.Lorentz force,in the exponential-polar coordinates,the numerical investigations were carried out by means of an alternative-direction implicit algorithm and a fast Fourier transform algorithm.The variation of the optimal interaction parameters with time were described based on calculated results,and the evolution of the flow field and the variation of the drag and lift forces on the cylinder surface in the control process were discussed.The results show that the suppression of vortex shedding,reduction in drag force,absorption of vibration and suppression of noise can be implemented by the optimal control.