Pressure Output Feedback Control of Tollmien–Schlichting Waves in Falkner–Skan Boundary Layers

Tol, H. J.; Kotsonis, Marios; Visser, Coen C. de

doi:10.2514/1.j057010

Cited by 5 publications

(5 citation statements)

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“…2013 b ; Tol et al. 2019), the feedforward design minimizes the local norm even more than the feedback one. Nevertheless, for both configurations, the minimization of the cost functional allowed the local norm of not to exceed, before , a threshold given by the norm at .…”

Section: Feedforward Versus Feedback Controlmentioning

confidence: 99%

“…2012; Tol et al. 2019), the robustness to stability for a feedback design obtained with a robust synthesis method is not a problem. Next, we examine performance robustness, which is a different issue.…”

Section: Feedforward Versus Feedback Controlmentioning

confidence: 99%

“…2013 b ; Vemuri et al. 2018; Tol, Kotsonis & de Visser 2019). In this case, though, there may be a significant time delay before the effect of actuation may be seen by the sensor, because perturbations are convected at a finite rate by the underlying base flow: the farther downstream is, the longer the delay.…”

Section: Introductionmentioning

confidence: 98%

“…2018 a ; Tol et al. 2019; and many others), a synthesis method dating back to the 1960s (Kalman 1964). Despite being theoretically optimal with respect to a performance criterion, this method comes with no guarantees on stability margins (Doyle 1978).…”

Section: Introductionmentioning

confidence: 99%

“…Tol et al. (2019) also obtained some unstable controllers when trying to control Tollmien–Schlichting (TS) waves in an incompressible two-dimensional (2-D) boundary layer using LQG synthesis on a feedback set-up. Belson et al.…”

Section: Introductionmentioning

confidence: 99%

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Reactive control of second Mack mode in a supersonic boundary layer with free-stream velocity/density variations

et al. 2023

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We consider closed-loop control of a two-dimensional supersonic boundary layer at $M=4.5$ that aims at reducing the linear growth of second Mack mode instabilities. These instabilities are first characterized with local spatial and global resolvent analyses, which allow us to refine the control strategy and to select appropriate actuators and sensors. After linear input–output reduced-order models have been identified, multi-criteria structured mixed $H_{2}$ / $H_{\infty }$ synthesis allows us to fix beforehand the controller structure and to minimize appropriate norms of various transfer functions: the $H_{2}$ norm to guarantee performance (reduction of perturbation amplification in nominal condition), and the $H_{\infty }$ norm to maintain performance robustness (with respect to sensor noise) and stability robustness (with respect to uncertain free-stream velocity/density variations). Both feedforward and feedback set-ups, i.e. with estimation sensor placed respectively upstream/downstream of the actuator, allow us to maintain the local perturbation energy below a given threshold over a significant distance downstream of the actuator, even in the case of noisy estimation sensors or free-stream density variations. However, the feedforward set-up becomes completely ineffective when convective time delays are altered by free-stream velocity variations of $\pm$ 5 %, which highlights the strong relevance of the feedback set-up for performance robustness in convectively unstable flows.

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