Control of coherent structures in reattaching laminar and turbulent shear layers

Roos, Frederick W.; Kegelman, Jerome T.

doi:10.2514/3.9553

Cited by 147 publications

(28 citation statements)

References 9 publications

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“…This is the case in the work of Miranda et al (2005) who use an oscillating flap and find that the optimal forcing frequency for a sharp-edged airfoil is, as in the previous studies, equal to the frequency of the vortex shedding which is naturally developed in the uncontrolled post-stall flow. Miranda et al (2005) also show that the same conclusion can be drawn from the early studies of Seifert and Pack (1999) and Roos and Kegelman (1986) provided that a proper calculation of the Strouhal number is proceeded. Audier et al (2012) exhibit a significant lift increase on a NACA 0012 profile when the forcing frequency applied through a surface DBD actuator is equal to the vortex shedding one.…”

Section: Introductionsupporting

confidence: 67%

Experimental closed-loop control of separated-flow over a plain flap using extremum seeking

Chabert¹,

Dandois

Garnier

2016

Exp Fluids

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Section: Introductionsupporting

confidence: 67%

Experimental closed-loop control of separated-flow over a plain flap using extremum seeking

Chabert¹,

Dandois

Garnier

2016

Exp Fluids

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“…It has been shown in previous investigations 3 that a rectangular roughness element submerged in a subsonic flat-plate boundary layer causes spontaneous vortex shedding downstream, similar to what happens in the wake of a backward facing step. 20 Flow over a cavity has been investigated actively for the acoustic resonance mechanisms. For a proper cavity length to height ratio, the cavity also leads to spontaneous vortex shedding downstream.…”

Section: Resultsmentioning

confidence: 99%

Effects of Cavities and Protuberances on Transition over Hypersonic Vehicles

Chang

Choudhari

et al. 2011

41st AIAA Fluid Dynamics Conference and Exhibit

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Surface protuberances and cavities on a hypersonic vehicle are known to cause several aerodynamic or aerothermodynamic issues. Most important of all, premature transition due to these surface irregularities can lead to a significant rise in surface heating. To help understand laminar-turbulent transition induced by protuberances or cavities on a Crew Exploration Vehicle (CEV) surface, high-fidelity numerical simulations are carried out for both types of trips on a CEV wind tunnel model. Due to the large bluntness, these surface irregularities reside in an accelerating subsonic boundary layer. For the Mach 6 wind tunnel conditions with a roughness Reynolds number Re kk of 800, it was found that a protuberance with a height to boundary layer thickness ratio of 0.73 leads to strong wake instability and spontaneous vortex shedding, while a cavity with identical geometry only causes a rather weak flow unsteadiness. The same cavity with a larger Reynolds number also leads to similar spontaneous vortex shedding and wake instability. The wake development and the formation of hairpin vortices for both protuberance and cavity were found to be qualitatively similar to that observed for an isolated hemisphere submerged in a subsonic, low speed flat-plate boundary layer. However, the shed vortices and their accompanying instability waves were found to be slightly stabilized downstream by the accelerating boundary layer along the CEV surface. Despite this stabilizing influence, it was found that the wake instability spreads substantially in both wall-normal and azimuthal directions as the flow is evolving towards a transitional state. Similarities and differences between the wake instability behind a protuberance and a cavity are investigated. Computations for the Mach 6 boundary layer over a slender cylindrical roughness element with a height to the boundary layer thickness of about 1.1 also shows spontaneous vortex shedding and strong wake instability. Comparisons of detailed flow structures associated with protuberances at subsonic and supersonic edge Mach numbers indicate distinctively different instability mechanisms. Nomenclature

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“…These peaks correspond to the forcing frequency (n ≈ 0.5) and its harmonics and subharmonics. Generally, the moderate reduction levels observed in this study can be explained with a reduced effectiveness of the shear-layer excitation in the transitional range [8].…”

Section: Resultsmentioning

confidence: 91%

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

Neumann

2003

Proc Appl Math and Mech

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Control of coherent structures in reattaching laminar and turbulent shear layers

Cited by 147 publications

References 9 publications

Experimental closed-loop control of separated-flow over a plain flap using extremum seeking

Experimental closed-loop control of separated-flow over a plain flap using extremum seeking

Effects of Cavities and Protuberances on Transition over Hypersonic Vehicles

On time‐dependent behaviour of controlled turbulent flow with separation and reattachment

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