Comparison of a separated flow response to localized and global-type disturbances

Monnier, Bruno; Williams, David R.; Weier, Tom; Albrecht, Thomas

doi:10.1007/s00348-016-2199-4

Cited by 5 publications

(7 citation statements)

References 14 publications

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“…In addition, Monnier et al (2016) reported that the circulatory force on a wing in response to an impulse-like pitching motion also follows the same lift reversal behavior as the AFC actuators (e.g. synthetic and burst-blowing jets).…”

Section: Introductionmentioning

confidence: 92%

“…Next we apply the Proper Orthogonal Decomposition (POD) to the transient case of the single burst actuation to gain additional insight into the modes that are responsible for the lift and pitching moment reversal. In a similar experiment, Monnier et al (2016) reported that the temporal coefficient of the second Proper Orthogonal Decomposition (POD) mode correlates with the negative of the lift coefficient variation following a singleburst input. The POD method can reduce a large number of interdependent variables to a much smaller number of independent modes, while retaining as much as possible the variation in the original variables (Kerschen et al 2005).…”

Section: Proper Orthogonal Decomposition (Pod) Of the Flow Fieldmentioning

confidence: 99%

“…When the system is linear and time invariant, the impulse response can be used in a convolution integral to predict the response from any arbitrary input. The impulse-like disturbances excite a broad spectrum of modes within the separated flow, which can trigger multiple instabilities (Monnier et al 2016). Amitay & Glezer (2002a) conducted experiments on a stalled wing using this approach, and identified an initial reversal in the lift increment following a short burst (single-burst) input from a synthetic jet actuator prior to the lift increasing.…”

Section: Introductionmentioning

confidence: 99%

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Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst

Williams

Silva

et al. 2017

47th AIAA Fluid Dynamics Conference

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The separated flow response to single and multiple burst mode actuation over a 2-D airfoil at 12 o angle of attack was studied experimentally. For the single-burst actuation case, surface pressure signals were correlated with the flowfield observations of the roll-up and convection of a large-scale vortex structure that follows the actuator burst input. A spatially localized region of high pressure occurs below and slightly upstream of a "kink" that forms in the shear layer, which is responsible for the lift reversal that occurs within 2.0t + after the burst signal was triggered. Proper orthogonal decomposition of the single-burst flow field shows that the time-varying coefficients of the first two modes correlate with the negative of the lift coefficient and pitching moment coefficient. The dynamic mode decomposition (DMD) of the single-burst flow field data identified the modes related to the kinetic energy growth of the disturbance. The mode with the largest growth rate had a Strouhal number close to that associated with the separation bubble dynamics. However, when multiple bursts are used to control the separation, the interactions between the bursts were observed which depend on the time intervals between the bursts. The convolution integral and DMD were performed on the multiburst flow field datasets. The results indicate that the nonlinear burst-burst interaction only affects the reverse flow strength within the separation bubble, which is related to the main trend of the lift. On the other hand, the linear burst-burst interaction contributes to the high-frequency lift variation associated with the bursts.Key words: Authors should not enter keywords on the manuscript, as these must be chosen by the author during the online submission process and will then be added during the typesetting process (see http://journals.cambridge.org/data/relatedlink/jfmkeywords.pdf for the full list) †

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Section: Introductionmentioning

confidence: 92%

Section: Proper Orthogonal Decomposition (Pod) Of the Flow Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst

Williams

Silva

et al. 2017

47th AIAA Fluid Dynamics Conference

Self Cite

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“…8, the time delay to reach the maximum lift increment depends on the separated flow dynamics, and not on the type of actuation. The initial time delay is the time required for the shear-layer perturbation to evolve into a large-scale vortex that convects over the surface [48,56]. Therefore, it is the fluid dynamic response of the shear layer and separated region that determines the lift response time: not the actuator.…”

Section: A System Response To An Actuator Pulsementioning

confidence: 99%

Alleviating Unsteady Aerodynamic Loads with Closed-Loop Flow Control

Williams

King

2018

AIAA Journal

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The practical benefits and issues related to controlling unsteady loads in gusting flows with active flow control actuators are discussed. Recent methods used to model the response of flight and road vehicles to unsteady flow disturbances, as well as modeling approaches for the dynamic effects of active flow control, are presented in the framework of a feedforward/feedback control architecture. Limitations of the achievable control performance are discussed. For instance, the lift reversal and the delay time required for the lift increment to reach its maximum value are responsible for limiting the bandwidth that can be achieved with active flow control of separated flows. An estimate of the practical gust bandwidth that can be controlled with aircraft is made.

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“…13,14 Holmes 15 designed a wind tunnel capable of generating the sinusoidal streamwise gust with the movement of the tunnel wall. Granlund et al 16 and Monnier et al 17 and Kerstens et al 18 and Strangfeld et al 8 obtained the sinusoidal streamwise gust by oscillating the free stream with the louvers system. These scholars observed deviations in unsteady lift amplitudes and phases from theoretical predictions at high reduced frequencies or at large angles of attack.…”

mentioning

confidence: 99%

Experimental investigation on the unsteady lift of an airfoil in a sinusoidal streamwise gust

Yang

et al. 2017

Physics of Fluids

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The unsteady lift of a stationary airfoil encountering a sinusoidal streamwise gust is experimentally investigated under attached flow conditions. The airfoil has an NACA 0015 profile with a chord length c = 0.5 m. The Reynolds number of the main flow is in the range of 198 000 ⩽ Re ⩽ 331 000. The reduced frequency of the perturbation ω ranges from 0.047 to 0.392. The results show that the fluctuation in the lift force reduces very much at the high frequency. It can be attributed to a significant reduction in the fluctuating pressure difference over the front half of the airfoil. Thus experimental aerodynamic admittance functions for the unsteady lift are lower than theoretical predictions relating to this case with increasing reduced frequencies, though experimental values are close to theoretical values at low reduced frequencies.

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Comparison of a separated flow response to localized and global-type disturbances

Abstract: to generate very similar Lagrangian flow structures. The results suggest a certain degree of universality in the POD modes/flow structures for the separated flow over an airfoil, irrespective of the type of excitation.

Cited by 5 publications

References 14 publications

Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst

Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst

Alleviating Unsteady Aerodynamic Loads with Closed-Loop Flow Control

Experimental investigation on the unsteady lift of an airfoil in a sinusoidal streamwise gust

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