Adaptive control of low-Reynolds number aerodynamics in uncertain environments: Part 1. Disturbance regimes and flow characteristics

For a wing operating under a chord Reynolds-number condition of O(104) or lower, flow separation often results due to uncertain free-stream conditions, such as wind gust. Consequently, aerodynamic performance can fluctuate greatly. In this study, we focus on the control of aerodynamic forces on a SD7003 airfoil due to free-stream fluctuations at the chord Reynolds number of 1000 using a dielectric barrier discharge (DBD) actuator. In Part 1, based on open-loop flow responses, the Strouhal number and reduced frequency of the free-stream unsteadiness characterize disturbance regimes: transition of the flow regimes along with qualitative changes in lift-drag characteristics, reflecting the changes in stall vortex patterns. In parallel, a closed-loop controller adopting a penalty-based adaptive law, based on linearized system parameter estimates, is also investigated. This combination of minimal modeling and adaptive parameterization can suppress substantial oscillations in aerodynamic forces. The mitigation of fluctuating forces is achieved via two means: modifying wall pressure near the actuator and promoting reduced, out-of-phase vortex evolution. These two mechanisms combine differently depending on the disturbance regimes. The results offer improved understandings of flow physics for developing effective control mechanisms.