Control of the separated flow downstream of a backward-facing step using visual feedback

Abstract

The separated flow downstream of a backwardfacing step is controlled using visual information for feedback. This is done when looking at the flow from two vantage points. Flow velocity fields are computed in real time and used to yield inputs to a control loop. This approach to flow control is shown to be able to control the detached flow in the same way as has been done before by using the area of the recirculation region downstream of the step as the input for a gradient descent optimization scheme. Visual feedback using real-time computations of two-dimensional velocity fields also allows for novel inputs in the feedback scheme. As a proof of concept, the spatially averaged value of the swirling strength λ Ci is successfully used as the input for an automatically tuned proportional-integral-derivative controller.

Closed-loop separation control over a sharp edge ramp using genetic programming

“…This result shows that the observation of the back flow area is equivalent to the observation of the variation of the separation length. This is in agreement with the recent work of Gautier and Aider (2013). Furthermore, the monotonic evolution of the back flow area versus the momentum coefficient ( Fig.…”

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

“…For a BFS whose separating boundary layer has 3-D flow fluctuations at sufficiently high Reynolds number, the wake flow exhibits global instability and is an "oscillator" flow; most previous studies agree on the existence of a shedding/step mode and a lower frequency flapping or bubble pumping mode [13][14][15]. Previous numerical [15,16] and experimental [8,[17][18][19] feedback control studies have been performed; with the exception of [15], the sensor signal has been either based on wake velocity measurements or a measure of the reattachment length.…”

“…In numerical simulations, optimal control in which the adjoint equations are solved can be used [9,22], but these methods cannot be extended to experiments. Finally, sensor signals based on flow field, rather than body-mounted sensing, can provide extra insights into the flow physics [19], but again will not be applicable in real moving-body experiments outside of the wind/water tunnel.…”

Closed-loop separation control using machine learning

“…Its offline and online accuracy has been demonstrated and detailed by Champagnat et al (2011) and Gautier & Aider (2014b). Furthermore this acquisition method was successfully used in Davoust, Jacquin & Leclaire (2012), Gautier & Aider (2013a) and Gautier & Aider (2014a). Velocity fields are computed over an area of (17.2 × 4.6) × 10 −4 m 2 which translates into a (9 × 3)h 2 area.…”