Feedback control of slowly-varying transient growth by an array of plasma actuators

Abstract

Closed-loop feedback control of boundary layer streaks embedded in a laminar boundary layer and experiencing transient growth, which is inherent to bypass boundary layer transition, is experimentally investigated. Streaky disturbances are introduced by a spanwise array of cylindrical roughness elements, and a counter disturbance is provided by a spanwise array of plasma actuators, which are capable of generating spanwise-periodic counter rotating vortices in the boundary layer. Feedback is provided by a spanwise array of shear stress sensors. An input/output model of the system is obtained from measurements of the boundary layer response to steady forcing, and used to design and analyze a proportional-integral controller, which targets a specific spanwise wavenumber of the disturbance. Attention is directed towards a quasi-steady case in which the controller update is slower than the convective time scale. This choice enables addressing issues pertinent to sensing, actuation, and control strategy that are also relevant to the control of unsteady disturbances but without the full complexity of transient effects. The feedback controller and plasma actuators perform well, attenuating the streamwise streaks both in the vicinity of the sensors and farther downstream. The controller remains effective for a range of off-design flow conditions, such as when the free-stream velocity is varied.

Geometry optimization of linear and annular plasma synthetic jet actuators

“…3). The easiest system achieving such effect provides two linear couples of electrodes, in a symmetrical layout [31][32][33][34]. Previous works have established that DBD plasma actuators can influence the fluid dynamics of an airfoil for traveling speeds up to 20 m/s [34][35][36].…”

Reactive control of isolated unsteady streaks in a laminar boundary layer

“…Toward resolving this limitation and the implementation of streak control, in a precursor to the present work, Hanson et al (2010) and Osmokrovic, Hanson & Lavoie (2015), demonstrated that plasma actuator arrays could be used to effectively reduce the energy contained within targeted modes of spanwise-periodic streak disturbances generated using a static array of roughness elements at steady state. Furthermore, Hanson et al (2014) provide an experimental demonstration of feedback control using a proportional integral (PI) controller which actively senses and controls steady and slowly varying streak disturbances introduced by a spanwise array of roughness elements. Targeting the fundamental mode disturbance for reduction (based on the roughness-element spacing), the mode's disturbance energy is shown to be reduced by 94 % at the feedback sensor location in Hanson et al (2014).…”

“…Furthermore, Hanson et al (2014) provide an experimental demonstration of feedback control using a proportional integral (PI) controller which actively senses and controls steady and slowly varying streak disturbances introduced by a spanwise array of roughness elements. Targeting the fundamental mode disturbance for reduction (based on the roughness-element spacing), the mode's disturbance energy is shown to be reduced by 94 % at the feedback sensor location in Hanson et al (2014). Osmokrovic et al (2015) provided an investigation into the geometry and operating parameters used in dielectric barrier discharge plasma actuators, similar to those used here.…”

“…Furthermore, a comprehensive assessment of the limited control bandwidth is made. This work builds upon the steady/slowly varying feedback disturbance control of Hanson et al (2014). To minimize the complexity of the experimental arrangement, a model problem is considered where a localized, rather than spanwise periodic, disturbance is produced using a single roughness element that is controlled by a pair of single-dielectricbarrier-discharge (SDBD) actuators.…”

Robust control of flow separation over a pitching aerofoil using plasma actuators

“…However, the latter, which is the chosen output in both Benard and Moreau (2009) and Cho and Shyy (2011), cannot be measured in real-time in practical flow control applications. Our objective is to solve the problem of directly controlling the unsteady flow separation using real-time velocity measurements, which are available in realistic applications (see, for example, Hanson et al, 2014;Segawa et al, 2010). We propose this flow separation problem as a practical application of the new theoretical results in Marino and Tomei (2015).…”