Organized vortex motion in periodically perturbed turbulent separated flow over a backward-facing step

Yoshioka, Shuya; Obi, Shinnosuke; Masuda, Shinji

doi:10.1016/s0142-727x(01)00092-3

Cited by 67 publications

(35 citation statements)

References 14 publications

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“…Although the flow conditions and actuation level differ (the latter cannot be directly compared due to different slot widths and definitions of the forcing amplitude), the curve for forcing level A j = 0.3 agrees reasonably well with the experimental data. Yoshioka, Obi & Masuda (2001) report a maximum reduction in reattachment length of 30 % for a forcing amplitude A j = 0.3, which provides further support for the present results. The reduction of the reattachment length is linked to increased turbulent stresses near separation, which lead to a higher growth rate of the shear layer.…”

Section: 2supporting

confidence: 89%

Feedback control for form-drag reduction on a bluff body with a blunt trailing edge

2012

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The objective of this numerical study is to increase the base pressure on a backwardfacing step via linear feedback control, to be ultimately translated to a drag reduction on a blunt-based bluff body. Two backward-facing step cases are simulated: a laminar two-dimensional (2D) flow at a Reynolds number of Re θ = 280, and a turbulent three-dimensional (3D) flow at Re θ = 1500 using large-eddy simulation. The control is effected by a full-span slot jet with zero-net-mass-flux, and two jet locations are examined. Linear system identification is performed to characterize the flow response to actuation, used to synthesize a control law. The control strategy is based on the premise that an attenuation of the instantaneous pressure fluctuations on the base of the step should lead to an increase in the time-averaged base pressure. Open-loop harmonic forcing is examined within a broad frequency range for both the 2D and 3D flows, which are found to respond differently to actuation. The controllers based on disturbance attenuation lead to sensible increases in base pressure (up to 70 % in 2D and 20 % in 3D) with higher efficiency than the best results achieved in open-loop. The results support the conjecture about the link between the base pressure fluctuations and mean, although it is shown that such a black-box model approach is not suitable for optimization without further physical insight.

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Section: 2supporting

confidence: 89%

Feedback control for form-drag reduction on a bluff body with a blunt trailing edge

2012

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“…Experimental studies for the same flow by Yoshioka et al [23] demonstrate a maximum reduction in the baseline separation length of around 30 per cent, well reproduced by the simulation. Phase-averaged vortical patterns reported by Dejoan & Leschziner [7] are remarkably similar to those in figure 2, despite the very different geometry, large differences in flow conditions, especially in the ratio of pre-separation boundary-layer momentum thickness to the length of the separated shear layer, and a factor 30 difference in the respective Reynolds numbers.…”

Section: Slot Jetssupporting

confidence: 66%

“…Yet, Yoshioka et al [23] show this actuation frequency to give the maximum reduction in recirculation length, supporting the supposition that the shear-layer mode is of subordinate importance to the optimum actuation frequency. Consistently, Neumann & Wengle [22] also report, based on a range of LES computations for a flow separating from a curved step, an optimal actuation frequency at St H = 0.2, which corresponds to St L = 0.8.…”

Section: Slot Jetsmentioning

confidence: 88%

Simulation of slot and round synthetic jets in the context of boundary-layer separation control

Leschziner

Lardeau

2011

Phil. Trans. R. Soc. A.

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Synthetic jets-also referred to as mass-less jets-offer the potential of effective, on-demand, fluid-based control of separating boundary layers on highly loaded aerodynamic surfaces, without the need for a mass source. However, the control authority that may optimally be derived from such jets, and any generality of the underlying flow physics are obscured by the wide range of geometric and flow parameters that contribute to their performance characteristics. The present article reviews the state-of-the art in the area of computational modelling and simulation of synthetic jets, with emphasis placed on key fluid-mechanics phenomena. The review is divided into two principal parts, one focusing on slot jets and the other on round jets. Within the latter part, ongoing research by the authors on the simulation of synthetic jets discharged into a separated boundary layer is highlighted as an example of the current status in this area.

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“…4 shows the X-coordinate at which U/U 0 measured at Y/H = 0.06 (measuring point nearest the bottom wall) changes its sign. This location is regarded as the reattaching point of the flow that is separated at the downstream edge of the T-junction (8) , and the distance between X/B = 0 and this X-coordinate is defined as the reattaching length L. Figure 5 shows the variation of L/B against AR and VR. L increases as VR is increased but it is quite insensitive to AR.…”

Section: Experimental Apparatus and Proceduresmentioning

confidence: 99%

Three-Dimensional Structure of Turbulent Flow in Mixing T-junction

Hirota

Asano

Nakayama

et al. 2006

JSME international journal. Ser. B, Fluids and thermal engineer

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Experimental results on the turbulent mixing of hot and cold airflows in a T-junction are reported, which simulates the HVAC unit used in an automobile air conditioning system. Experiments are conducted keeping Reynolds number and temperature of the main flow at 2.5 × 10 4 and 12• C, respectively, and the velocity of the branch flow (60 • C) is changed for three velocity ratios of 0.5, 1 and 2. The flow from the branch is separated at the edge of the T-junction and forms a large separation bubble. Longitudinal vortices are formed around this separation bubble, thus the flow field has a three-dimensional structure. In spite of such a complex flow field, the mean temperature in the thermal mixing layer shows quite uniform distributions in the spanwise direction, and the strong turbulence produced around the separation bubble does not work effectively to the thermal mixing of hot and cold airflows.

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Organized vortex motion in periodically perturbed turbulent separated flow over a backward-facing step

Cited by 67 publications

References 14 publications

Feedback control for form-drag reduction on a bluff body with a blunt trailing edge

Feedback control for form-drag reduction on a bluff body with a blunt trailing edge

Simulation of slot and round synthetic jets in the context of boundary-layer separation control

Three-Dimensional Structure of Turbulent Flow in Mixing T-junction

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