Simulation of Active Drag Reduction for a Square-Back Vehicle

Wassen, Erik; Eichinger, Sándor; Thiele, Frank

doi:10.1007/978-3-642-11735-0_16

Cited by 26 publications

(20 citation statements)

References 17 publications

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“…from which one can estimate the apparent mean bubble length. For the present Reynolds number, the measured L r = 1.50 ± 0.01 agrees with other numerical or experimental studies (Wassen et al 2010;Lahaye et al 2014;Volpe et al 2015) of this flow configuration. From the v distribution in figure 5(b), we conclude that the mean wake is dominated by a large clock-wise recirculating motion.…”

Section: Baseline Flowsupporting

confidence: 91%

“…Without curved appendices, steady blowing increases base pressure by approximately 5 %, reducing the drag by at most 3 % in the range C µ ∈ [0, 0.015], corresponding to blowing velocities V j /U o ∈ [0, 1.1]. This performance agrees with drag reductions obtained by previous studies with similar steady jet amplitudes in axisymmetric or square-back models (Freund & Mungal 1994;Wassen et al 2010;Krentel et al 2010). In the case of steady blowing, while no difference is measured up to C µ ∼ 7.5 × 10 −3 (V j /U o ∼ 0.55), the Coanda effect improves base pressure recovery at higher blowing velocities.…”

Section: Impact On the Base Pressure And Wake Flowsupporting

confidence: 88%

Bluff body drag manipulation using pulsed jets and Coanda effect

et al. 2016

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The impact of fluidic actuation on the wake and drag of a 3D blunt body is experimentally investigated. The wake is forced by jets pulsed tangentially to the main flow with variable frequency and velocity. Depending on the forcing conditions, two flow regimes can be identified. First, for a broadband range of frequencies comprising the natural wake instabilities, the convection of the jet structures enhances wake entrainment, shortening the recirculating flow length with an augmentation of the bluff body drag. Further increase of the actuation frequency induces a wake fluidic boat-tailing by shear-layer deviation. It additionally lowers turbulent intensity and entrainment of high momentum fluid in the shear layer, leading to an overall reduction of the wake fluctuating kinetic energy. The association of both mechanisms is responsible for a raise of base pressure and decrease of the model's drag. The physical features of such regimes are discussed on the basis of drag, pressure and velocity measurements at several upstream conditions and control parameters. By adding curved surfaces at the jet outlets to take advantage of the so-called Coanda effect, periodic actuation can be further reinforced leading to drag reductions of about 20 % in unsteady regime. In general, the unsteady Coanda blowing not only intensifies the base pressure recovery but also preserves the effect of unsteady high frequency forcing on the turbulent field. The present results encourage the development of fluidic control in road vehicles' aerodynamics as well as provide a complement to our current understanding of bluff body drag and its manipulation.Comment: 47 pages, 35 figures, extended versio

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“…Furthermore, an elongated recirculation area (black solid line) is clearly visible. The obtained recirculation length L r = 1.15h (reported in Table 1) agrees well with previous studies [58,36,57]. The cross-stream velocity contour-plot shows the variability of the flow in the wall normal direction.…”

Section: Baseline Flowsupporting

confidence: 90%

“…This tendency is inverted for the "moderate frequency" region St A ∈ [0.15, 0.6], where the drag decreases. Again, an opposite tendency is obtained for F D and p i which well agrees with experimental and numerical investigations of the literature [52,58]. The gray area in Figure 9 represents a positive drag difference, while the white area represents a negative drag difference.…”

Section: Open-loop Investigationsupporting

confidence: 88%

Sliding mode control applied to a square-back Ahmed body

Chovet

Feingesicht

Plumjeau

et al. 2020

European Journal of Mechanics - B/Fluids

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We consider the first closed-loop separation control experiment on an Ahmed body using a robust, modelbased strategy called "sliding mode control" (SMC). The goal is to reduce and further maintain the aerodynamic drag of the square-back Ahmed body flow at Re h = 9 × 10 4 (based on the body height). This study also investigates the practical feasibility of this approach which shows a great promise for industrial applications. The flow is manipulated by a slotted jet placed on the top trailing edge, combined with a predefined angle direction, and sensed by a drag balance. Base pressure and lift measurements are also obtained in real-time. The interaction between the air jet actuator and the mean near-wake flow are depicted by means of Particle Image Velocimetry. In order to compare this closed-loop strategy we first present two open-loop ones. Continuous blowing is initially used to directly influence the recirculation area and hence achieve a reduction in the drag. Approximately a drag reduction of 8% is accomplished making this approach the "optimal case" control strategy. However, because steady blowing mechanisms lead to the highest energy consumption scheme, this strategy will only serve as the first open-loop control reference. The second open-loop strategy involves three periodic forcing frequencies, St A = 0.0765, 0.135 & 0.405. The influence of these frequencies on the near-wake, and its further drag modification, will be further examined. The proposed sliding mode control (closed-loop strategy) is applied to the same Ahmed body configuration and compared to the open-loop cases. It will be designed on the basis of a simplified input-output model which was recently defined for another flow control application. Last, a second experiment is conducted so to show the disturbance rejection of the controller, corroborating the robustness and efficiency of this control approach. Its limitations and difficulties on an experimental setup are also discussed. SMC is able to reduce and maintain the drag to a desire set-point regardless external flow perturbations. Our control strategy was recently used in another context (flow reattachement on a wing) with the same robustness. These successes make guess it is applicable to multiple experimental and industrial contexts.

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“…They have been observed in the separated flows over the rear window of a notch-back vehicle (Lawson, Garry & Faucompret 2007) or past a three-dimensional double backward facing step (Herry, Keirsbulck & Paquet 2011). High degrees of asymmetry have also been obtained in experiments and numerical simulations of the flow past three-dimensional geometries despite the symmetry of the set-up (Lee, Paik & Lee 2009;Wassen, Eichinger & Thiele 2010); they might be the signature of a comparable instability. Analogous dynamics in the natural wake past the reference Ahmed geometry (Ahmed, Ramm & Faitin 1984) are also reported in Part 1 of this study (Grandemange, Gohlke & Cadot 2013b).…”

mentioning

confidence: 90%

Turbulent wake past a three-dimensional blunt body. Part 2. Experimental sensitivity analysis

2014

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The sensitivity of the flow around three-dimensional blunt geometry is investigated experimentally at Reynolds number $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}9.2\times 10^4$. Vertical and horizontal control cylinders are used to disturb the natural flow which is the superposition of two reflectional symmetry breaking states (see Part 1 of this study, Grandemange, Gohlke & Cadot, J. Fluid Mech., vol. 722, 2013b, pp. 51–84). When the perturbation breaks the symmetry of the set-up, it can select one of the two asymmetric topologies so that a mean side force is found. When the reflectional symmetry is preserved, some positions of horizontal and vertical control cylinders alter the natural bi-stability of the flow which may result in drag reduction. In addition, it is found that the horizontal perturbation affects the lift force especially when the top and bottom mixing layers are disturbed. The ability of the disturbances to suppress the bi-stable behaviour is discussed and, introducing a formalism of induced drag, a quantification of the impact on the drag of the cross-flow forces observed for the natural bi-stable wake is suggested. Finally, a general concept for a control strategy of separated flows past three-dimensional bluff bodies can be drawn up from these analyses.

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Simulation of Active Drag Reduction for a Square-Back Vehicle

Cited by 26 publications

References 17 publications

Bluff body drag manipulation using pulsed jets and Coanda effect

Sliding mode control applied to a square-back Ahmed body

Turbulent wake past a three-dimensional blunt body. Part 2. Experimental sensitivity analysis

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