http://cwrowley.princeton.edu/papers/Cattafesta-PAS08.pdf

Active control of flow-induced cavity oscillations

An adaptive disturbance rejection algorithm is developed for the standard control problem The multiple input-multiple output (MIMO) system and controller are represented as ARMARKOV/Toeplitz models, and the parameter matrix of the compensator is updated online by means of a gradient algorithm The algorithm requires minimal knowledge of the plant, specifically, the numerator of the ARMARKOV model of the transfer function from the control inputs to the performance variables is required No knowledge about the spectrum of the disturbance is needed Experimental results demonstrating tonal and broadband disturbance rejection in an acoustic duct are presented

Adaptive disturbance rejection using ARMARKOV/Toeplitz models

First-principle-based models of the dynamics of flow systems are often of limited use for model-based control design, not only because of their nonlinear and infinite-dimensional nature, but also because the control input is generally specified as a boundary condition. Proper orthogonal decomposition and Galerkin projection are among the most effective and commonly used methods to obtain reduced-order models of flow dynamics. However, the final form of these models may not account for the presence of a forcing or control input. From a control design perspective, it is desirable to obtain a reduced-order model in which the control input appears explicitly in the dynamic equations. In this paper, two methods for control input separation are introduced and comparatively evaluated in experimentally based reduced-order modeling of cavity flow, both in their ability to reconstruct the forced flowfield and to provide models suitable for feedback control design. The proposed methods, namely, 1) actuated proper orthogonal decomposition expansion and 2) L 2 optimization, extend the baseline flow model through the use of innovation vectors, which capture the deviation of the actuated flow from the baseline space. The new methods address some of the issues associated with the subdomain separation technique employed in our previous works. Linear-quadratic regulator controllers, built using models obtained from the new methods, have been tested on a cavity flow experiment. Although the new models perform satisfactorily and comparably to our previous models in terms of suppression of cavity tones, they offer a substantial advantage in terms of the required input power to achieve a similar or better performance.

Control Input Separation Methods for Reduced-Order Model-Based Feedback Flow Control

This work is focused on the development of a new control separation approach for reducedorder model based feedback control and its implementation in subsonic cavity flows. The model is derived by applying Proper Orthogonal Decomposition in conjunction with Galerkin projection of the Navier-Stokes equations onto the resulting spatial eigenfunctions. The new method adds the effect of the control input as an additional set of basis. The model is derived for the baseline and a forced flow condition. When the new model was tested numerically, the new separation method showed noticeable changes when the control input was introduced into the system. A feedback controller based on the LQR methodology was designed and tested experimentally in the GDTL subsonic cavity flow facility of The Ohio State University. For control design, 4 modes were sufficient to capture the main features of the cavity flow. While experimental result showed that the new separation approach has similar effect on the flow behavior as our previous approach, we believe that the new methodology is a more suitable procedure for deriving control-oriented models. Furthermore, the new model does not require identification of the control input region in the data used to derive the reduced order model, which is not possible in many flow control applications.

Reduced order model for feedback control of cavity flow - The effects of control input separation

We present a first attempt and preliminary results on the development and application of feedback control to high-speed and high Reynolds number axisymmetric jets. In particular, we demonstrate control authority on the near pressure field of a Mach 0.9 jet with a Reynolds number based on jet diameter of 7.8 × 10. Open-loop forcing experiments are presented wherein our in-house developed plasma actuators are shown to have two distinct effects on the near pressure field. At low forcing Strouhal numbers (StDF’s) near the jet column mode instability, a sharp peak in the pressure fluctuations is observed. At higher StDF’s (close to the initial-shear-layer instability) a broad minimum is observed in the nearfield pressure fluctuations, and especially in its axisymmetric mode. An online gradientbased extremum-seeking feedback control scheme is implemented; it uses the RMS of the azimuthal-mode-filtered pressure fluctuations to optimize the StDF. The actual cost function for optimization can be selected as the RMS of various individual pressure azimuthal modes, or a combination thereof. The controller can be setup to either seek a maximum or a minimum with negligible reconfiguration. Preliminary experimental results are presented to demonstrate satisfactory performance in both operating regimes. Starting from either side of the minimum or maximum, the controller is shown to drive the StDF to the respective optimum and maintain the value over time.

/pdf/towards-feedback-control-of-high-speed-and-high-reynolds-4h6r4aoas6.pdf

Towards Feedback Control of High-Speed and High-Reynolds-Number Jets

Actuation devices are crucial components of closed-loop flow control schemes. Synthetic jetlike actuators, which are commonly employed in cavity flow control, exhibit a dynamic response that, if ignored, may significantly affect the overall characteristics of the closed-loop system. This paper presents the development and implementation of a dynamic compensator for a synthetic jetlike compression driver actuator which has been successfully implemented for feedback control of subsonic cavity flows. A time-delay model of the actuator dynamics is obtained from experimental data using subspace-based identification methods. The model is designed to match the frequency response of the physical system in a frequency range of interest that covers the resonance frequencies of the cavity. The model is then used for the synthesis of a dynamic controller which employs a Smith predictor in conjunction with an H ∞ mixed-sensitivity design. Order reduction is applied to obtain a low-order digital controller amenable to real-time applications. The compensator is retrofitted to an existing cavity flow control architecture, and used to force the actuator output to closely follow the input commands, thereby compensating undesirable actuator dynamics. Experiments show that the integration of the actuator compensator within the cavity control system significantly improves closed-loop performance.

Dynamic Compensation of a Synthetic Jetlike Actuator for Closed-Loop Cavity Flow Control

This paper considers development of an dynamic compensator for a synthetic-jet-like compression driver actuator, which has been successfully used for feedback control of subsonic cavity flow. System identification and feedback control design are performed using the experimental data of actuator dynamics. Subspace-based identification method is implemented to construct an control-oriented actuator model containing time delay. The resulting model matches the physical system effectively in the frequency domain, covering the frequency range of cavity oscillation where the actuator operates. Based on a Smithpredictor-type control structure, H1 mixed-sensitivity method is employed to synthesize a feedback controller for the actuator system. The feedback controller forces the actuator output to closely follow a control signal generated by a cavity flow controller, thereby compensating the undesirable actuator dynamics. Integration of the actuator compensator with the cavity control system improves the overall control performance by reducing uncertainties caused by the actuator dynamics.

Dynamic Compensator for a Synthetic-Jet-Like Compression Driver Actuator in Closed-Loop Cavity Flow Control

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Dynamic Compensation of a Synthetic Jetlike Actuator for Closed-Loop Cavity Flow Control

Dynamic Compensator for a Synthetic-Jet-Like Compression Driver Actuator in Closed-Loop Cavity Flow Control