Ultra-local model-based control of the square-back Ahmed body wake flow

Abstract

This paper presents a new model-free control approach applied to a dynamical fluidic system. The main objective is to evaluate the ability of this closed-loop control technique to control the bistability of a turbulent wake flow past to a square-back Ahmed body. This bistable behavior occurs for some configurations depending mainly on the ground clearance. Due to the unsteady position of the wake vortex cores, the bistable phenomenon is responsible of a strong variation of the lateral force (drift force) and of a slight drag increase. Consequently, mitigating the wake symmetry-breaking modes can induce a substantial drag reduction. The feedback controller controls the drift using its ultralocal approximation and the estimation of its dynamics. The control signal is then applied to lateral blower actuators to suppress the spanwise bistability. The drift force is used as feedback to sense the wake flow, and concomitant velocity, forces, and pressure measurements are performed at a nominal Reynolds number of Reh = 2.86 × 105 to quantify and demonstrate the effectiveness of the present closed-loop control. Results show that for various actuation velocity ratios, the bistability suppression can lead to a drag reduction up to 2.5% with an energy consumption evaluated to be less than 0.6% of the aerodynamic power saving for the worst investigated case.

Effects of Rear Angle on the Turbulent Wake Flow between Two in-Line Ahmed Bodies

“…The / values for DB_0 and DB_35 is comparable to The length of the reverse flow region behind the isolated square back model is L r /H = 1.36. This value is comparable to L r /H = 1.39 reported in previous studies [10,38]. In the presence of a follower, the length of the reverse flow region behind the square back model (L r /H = 1.53) increased by 13%.…”

Mechanics of bluff body drag reduction during transient near-wake reversals

“…Moreover, the side-alternating control promotes the vortex shedding dynamics in the wake resulting in a detrimental impact on the drag. Similarly, Brackston et al (2016) with oscillating side flaps and Plumejeau et al (2019) also with pulsed jets have shown similar mixed 2 % drag reduction using similar feedback control with linear control methods. To mitigate the lateral bi-stable dynamics, only passive control methods have proven to be satisfyingly efficient in terms of associated drag reductions.…”

Robust active flow control over a range of Reynolds numbers using an artificial neural network trained through deep reinforcement learning

“…1 Since the pioneering work of Prandtl about the use of active flow control (AFC) for delaying boundary layer separation, 2 AFC has witnessed a fast growth and has become an increasingly important technology for the pursuit of industrial and sustainable solutions. 3 Prospective applications of AFC to problems of industrial and environmental importance include, to name a few, reducing the aerodynamic drag on aircrafts, 4,5 manipulating the vortex in the wake of bluff bodies, [6][7][8][9][10] and optimizing the design and performance of wind turbines [11][12][13] and gas turbines. 14 Nevertheless, finding efficient strategies for performing AFC remains a challenge.…”