Closed-loop computational fluid dynamics simulations with time-varying boundary conditions for circulation control

We develop a computational fluid dynamics (CFD) framework to design a feedback circulation control system to compensate for fluctuations in the fixed-wing aircraft caused by wind gusts. Circulation control actions are realized using dynamic boundary conditions in the CFD simulations. The dynamic flow responses with the circulation control are obtained by solving the unsteady Reynolds-averaged Navier-Stokes equations. The dynamic lift responses at several oscillation frequencies of wind gusts and the plenum chamber pressure, which controls the circulation, are also obtained. A system identification algorithm from control theory establishes the transfer functions corresponding to the frequency responses. Based on the transfer functions and the aerodynamic characteristics of circulation control, a feedback circulation control algorithm is designed. The performance of the feedback control system is verified by the CFD simulation coupled with the controller as time-varying boundary conditions. At each time step, the controller determines the parameters in the boundary condition according to the instantaneous lift calculated in the previous time step. The simulation results show that the circulation control effectively compensates for the lift perturbations caused by vertical directional wind gusts. The proposed unsteady CFD simulation frameworks provide high-fidelity evaluations of feedback control systems, and it will save costly efforts to set up unsteady wind-tunnel experiments.