Feedback shear layer control for bluff body drag reduction

Pastoor, Mark; Henning, Lars; Noack, Bernd R.; King, Rudibert; Tadmor, Gilead

doi:10.1017/s0022112008002073

Cited by 269 publications

(192 citation statements)

References 72 publications

(87 reference statements)

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“…In configuration B, with the jet acting at 45 degrees upwards, at the point of separation it is suggested that the size of the wake is increased by deflecting the shear layer upwards. Some theories regarding the influence of wake size on resultant body forces predict that a stretched wake will create increased base pressures by moving vortex structures away from the base surface and so reduced body drag forces (Pastoor 2008;Bearman 1983). Other published work (Rounmeas 2008) suggests that a reduction in wake size will increase base pressures and create lower drag forces.…”

Section: Balance Resultsmentioning

confidence: 99%

“…8 are a result of modification to this lower structure, and its interaction with the base surface in addition to the global reduction in wake size. In effect, the benefits of stretching the wake to move vortices further away from the base outlined by Bearman (1983) and Pastoor (2008), are, in this instance, created by the downward blowing of the jet weakening the lower vortex structure. The weakening of this structure is shown in the reduction in the magnitude of vorticity of the structure, comparing Fig.…”

Section: Pivmentioning

confidence: 99%

“…Often the goal of the investigations is to reduce the size of the wake (Roumeas 2008) in order to reduce drag, however in certain applications it can be argued that a stretched wake structure would create lower drag (Bearman 1983;Pastoor 2008), and no general rule for every bluff body can be applied. However for the bluff body model used in the work reported here a reduction in wake size has been shown to result in a reduction in drag force (Littlewood 2010).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

Littlewood

Passmore

2012

Exp Fluids

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Section: Balance Resultsmentioning

confidence: 99%

Section: Pivmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

Littlewood

Passmore

2012

Exp Fluids

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“…For flow control of the bluff body, drag reduction is closely associated with the shear layer instability [25]. To analyze the flow control mechanism relevant to the shear layer instability, Figure 5 shows the instantaneous iso-contours of local Mach number M l .…”

Section: Self-sustained Oscillations Along the Shear Layermentioning

confidence: 99%

“…From the control perspective, in order to increase the base pressure and reduce the drag, the alternating character of the wake has to be mitigated or delayed [25]. The wake instability is closely associated with the shear-layer instability, and suppression of vortex roll-up inside the shear layer is enabler to increase the base pressure.…”

Section: Characteristics Of Separated Shear-layer Evolutionmentioning

confidence: 99%

Large-eddy simulation of the compressible flow past a tabbed cylinder

Zhao

Sun

2012

Chin. Sci. Bull.

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The compressible flow past a tabbed cylinder has been studied numerically using large-eddy simulation for a free-stream Mach number M∞=0.75 and a Reynolds number based on the diameter Re=2×10 5 . Because of the passive control of the flow past a tabbed cylinder, the mean drag coefficient of tabbed cylinder is less than that of a corresponding circular cylinder with a drag reduction up to 33%. The fluctuating lift coefficient is greatly suppressed to be nearly zero. Drag reduction due to the shearing process prevails over that due to the compressing process in this flow. Through investigating the mechanisms relevant to passive control of the tab, it is found that suppression of the shear layer instability can lead to a higher-base-pressure distribution, which can reasonably be associated with drag reduction and suppression of the lift fluctuations. The analysis of convective Mach number and self-sustained oscillations phenomenon inside the shear layers indicates that both the compressible effect and high-frequency forcing result in suppression of the shear layer instability of tabbed cylinder. circular cylinder, shock wave, compressible turbulence, large-eddy simulation Citation:Xu C Y, Zhao L Q, Sun J H. Large-eddy simulation of the compressible flow past a tabbed cylinder.

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A generalized framework for reduced‐order modeling of a wind turbine wake

et al. 2018

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A reduced-order model for a wind turbine wake is sought from large eddy simulation data. Fluctuating velocity fields are combined in the correlation tensor to form the kernel of the proper orthogonal decomposition (POD). Proper orthogonal decomposition modes resulting from the decomposition represent the spatially coherent turbulence structures in the wind turbine wake; eigenvalues delineate the relative amount of turbulent kinetic energy associated with each mode.Back-projecting the POD modes onto the velocity snapshots produces dynamic coefficients that express the amplitude of each mode in time. A reduced-order model of the wind turbine wake (wakeROM) is defined through a series of polynomial parameters that quantify mode interaction and the evolution of each POD mode coefficients. The resulting system of ordinary differential equations models the wind turbine wake composed only of the large-scale turbulent dynamics identified by the POD. Tikhonov regularization is used to recalibrate the dynamical system by adding additional constraints to the minimization seeking polynomial parameters, reducing error in the modeled mode coefficients. The wakeROM is periodically reinitialized with new initial conditions found by relating the incoming turbulent velocity to the POD mode coefficients through a series of open-loop transfer functions. The wakeROM reproduces mode coefficients to within 25.2%, quantified through the normalized root-mean-square error. A high-level view of the modeling approach is provided as a platform to discuss promising research directions, alternate processes that could benefit stability and efficiency, and desired extensions of the wakeROM. KEYWORDSdynamical system, proper orthogonal decomposition, reduced-order model, wind turbine wake INTRODUCTIONPerformance of wind farms is highly correlated with the wake following a given wind turbine. 1,2 However, for the sake of design efficiency, wakes and wind plants are typically modeled with simplified engineering or empirical relationships. Wind turbine wakes are highly variable, combining effects from the atmospheric boundary layer, interacting with large rotating structures, and often subject to wake-to-wake interaction within a wind plant. 3 Further, wakes evolving from individual turbines are asymmetrical due to the inherent shear in the atmospheric boundary layer and reflect the specific nature of incoming inflow events that vary significantly with diurnal and seasonal cycles and affect the performance of other turbines in a wind plant. 4 Given the complexity of the wind turbine wake, a computationally efficient means of correctly modeling wake dynamics and interaction is crucial to meet the rapid pace at which wind energy is being adopted globally and to address persistent wind plant underperformance.Reduced-order modeling describes a wide range of approaches that approximate complex system dynamics of large or infinite degrees of freedom with a limited, and more manageable, number of degrees of freedom. For applications in turbulence, the goal ...

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Feedback shear layer control for bluff body drag reduction

Cited by 269 publications

References 72 publications

Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

Large-eddy simulation of the compressible flow past a tabbed cylinder

A generalized framework for reduced‐order modeling of a wind turbine wake

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