Adaptive Control of Separated Flow

Abstract

Adaptive closed-loop control is used to optimize the lift-to-drag ratio of post-stall separated flow over a NACA 0025 airfoil using multiple amplitudemodulated (AM) or burst-modulated (BM), zero-net-mass-flux (ZNMF) actuators that cover the central 33% span of the airfoil. A simplex optimization approach uses the lift and drag measured by a strain-gauge balance for feedback and searches for the optimal AM or BM actuation parameters in a closed-loop fashion. An energy penalty function based on the electrical power consumption of the actuators is added to the cost function to study the tradeoff between the aerodynamic performance and the power requirement. In the baseline post-stall separated flow over the airfoil, two dominant characteristic frequencies are identified via flow visualization and hot-wire anemometry: the convective instability of the separated shear layer and the global instability of the vortex shedding in the wake. Closedloop control increases the lift-to-drag ratio by a factor of 2-3 via smallamplitude AM and BM forcing of nonlinear interactions between these instabilities. I.

Capabilities of the dielectric barrier discharge plasma actuator for multi-frequency excitations

“…The amplitude of fluctuation is larger and then more difficult to be dissipated further downstream. Initially, it was expected that superposition or burst modulation are preferred if the objective is to act on two frequencies of the free flow (to act on the shear layer and wake instabilities as suggested by [14,29]). The present results highlight the non linear response of the actuator when it operates in ring modulation.…”

Wind-turbine wakes responding to stably stratified flow over complex terrain

“…[1,14,15]. Therefore, the effect of thermal stratifications in complex terrain can be investigated as next step.…”

“…As first step, we will discuss the characteristics of the velocity profile in relation to the hill position. Following [1], we define a speed up effect as a velocity increase, and a blockage effect and an adverse pressure gradient effect as a velocity decrease at luv and lee, in each case in relation to the reference velocity profile over homogeneous surface.…”

“…The deformation of the wind while passing over hilly terrain increases the turbulence and advects it leewards into possible wind-turbine wakes [1], [2]. Considering the ABL, the ambient turbulence impacts the fatigue loading of a wind turbine and controls the entrainment of ambient air into the wake and, therefore, its characteristics.…”

“…The individual impacts of complex terrain [1], [2] and of the ABL [3], [4], [5], [6] on windturbine wakes have been investigated in several studies within the last years. The deformation of the wind while passing over hilly terrain increases the turbulence and advects it leewards into possible wind-turbine wakes [1], [2].…”