Experimental study of the K-regime of breakdown in straight and swept wing boundary layers

Chernoray, Valery; Bakchinov, Andrey; Козлов, В. В.; Löfdahl, Lennart

doi:10.1063/1.1366667

Cited by 9 publications

(6 citation statements)

References 8 publications

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“…Therefore, their results are subject to the same limitations with respect to choosing the physically correct saddle point. However, on extending the straight wing and 30 • swept-wing experimental investigation of Chernoray et al (2001) to a 45 • swept-wing boundary-layer, Pratt et al (2001) recently showed results for spots, which in the linear domain are qualitatively similar to that in figure 6. While this lends some credibility to our saddle-point solutions, it should be emphasized once again that for a proof we still need a practically implementable collision check for three-dimensional wave packets.…”

Section: Spatio-temporal Analysis Of Primary Crossflow Vorticesmentioning

confidence: 85%

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On the spatio-temporal stability of primary and secondary crossflow vortices in a three-dimensional boundary layer

Koch¹

2002

J. Fluid Mech.

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To examine possible links between a global instability and laminar–turbulent breakdown in a three-dimensional boundary layer, the spatio-temporal stability of primary and secondary crossflow vortices has been investigated for the DLR swept-plate experiment. In the absence of any available procedure for the direct verification of pinching for three-dimensional wave packets the alternative saddle-point continuation method has been applied. This procedure is known to give reliable results only in a certain vicinity of the most unstable ray. Therefore, finding no absolute instability by this method does not prove that the flow is absolutely stable. Accordingly, our results obtained this way need to be confirmed experimentally or by numerical simulations. A geometric interpretation of the time-asymptotic saddle-point result explains certain convergence and continuation problems encountered in the numerical wave packet analysis. Similar to previous results, all our three-dimensional wave packets for primary crossflow vortices were found to be convectively unstable.Due to prohibitive CPU time requirements the existing procedure for the verification of pinching for two-dimensional wave packets of secondary high-frequency instabilities could not be implemented. Again saddle-point continuation was used. Surprisingly, all two-dimensional wave packets of high-frequency secondary instabilities investigated were also found to be convectively unstable. This finding was corroborated by recent spatial direct numerical simulations of Wassermann & Kloker (2001) for a similar problem. This suggests that laminar–turbulent breakdown occurs after the high-frequency secondary instabilities enter the nonlinear stage, and spatial marching techniques, such as the parabolized stability equation method, should be applicable for the computation of these nonlinear states.

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Section: Spatio-temporal Analysis Of Primary Crossflow Vorticesmentioning

confidence: 85%

“…Spatial DNS by Konzelmann (1990) removed this limitation and extended the results into the nonlinear regime. Recently Chernoray et al (2001) investigated spatio-temporal flow patterns in a straight and weakly swept-wing boundary layer experimentally.…”

Section: Spatio-temporal Analysis Of Primary Crossflow Vorticesmentioning

confidence: 99%

On the spatio-temporal stability of primary and secondary crossflow vortices in a three-dimensional boundary layer

Koch¹

2002

J. Fluid Mech.

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“…Thus, as we understand it, the most likely situation in the APG region has not been clarified. Chernoray et al (2001) have experimentally studied the influence of a 30 • sweep angle on K-breakdown in the APG region on a wing. Disturbances were triggered by roughness elements placed periodically along the spanwise direction at 30 % chord, and a single-frequency sound wave.…”

Section: Introductionmentioning

confidence: 99%

Transition mechanisms in a three-dimensional boundary-layer flow with pressure-gradient changeover

Fransson

Talamelli

Brandt³

et al. 2005

J. Fluid Mech.

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The laminar breakdown of a three-dimensional flat-plate boundary-layer flow with favourable and ensuing adverse pressure gradient (APG), generic for an infinite swept wing, is investigated in detail by means of spatial direct numerical simulations. Emphasis is on transition mechanisms in the region of adverse pressure gradient where the undistorted laminar base flow also becomes unstable with respect to Tollmien–Schlichting (TS) waves that are most amplified if two-dimensional with respect to the local streamwise direction. The influence of finite-amplitude crossflow vortices, coming from the region of favourable pressure gradient, on the TS instability properties is investigated. It turns out that crossflow-vortex-induced secondary instabilities are the most amplified disturbances even for low-amplitude vortex modes. The TS waves act as generators of fundamental low-frequency secondary modes, but are neither important for their growth nor for breakdown. As for active disturbance control, any method aiming at attenuating two-dimensional TS waves must fail. On the other hand, the passive upstream-flow-deformation technique also delays transition in the APG region.

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“…The spatial wave trains excited by local harmonic source are used to study the laminar-turbulent transition of a three-dimensional and modulated boundary layer. 2,3…”

Section: Introductionmentioning

confidence: 99%

“…The spatial wave trains excited by local harmonic source are used to study the laminar-turbulent transition of a threedimensional and modulated boundary layer. 2,3 The approach for the experiments with the controlled disturbances is also effective for high-speed flows. The first experiments with artificial disturbances at high-speed flow were provided by Kendall.…”

Section: Introductionmentioning

confidence: 99%

Evolution of localized artificial disturbance in 2D and 3D supersonic boundary layers

Yatskikh

Yermolaev

Kosinov

et al. 2018

Proceedings of the Institution of Mechanical Engineers, Part G:

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The evolution of a controlled broadband wave packet in flat-plate and swept-wing supersonic boundary layers was experimentally investigated at Mach number M = 2. The wave packet was introduced into the boundary layer by a localized pulse electrical discharge. The structure and evolution downstream of the wave packet were studied by hot-wire measurements. It was found that the wave packet has a symmetric shape in a flat-plate boundary layer, whereas there is asymmetry in case of a swept-wing one. The spectral analysis of the development of different modes of the wave packet was provided.

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Experimental study of the K-regime of breakdown in straight and swept wing boundary layers

Cited by 9 publications

References 8 publications

On the spatio-temporal stability of primary and secondary crossflow vortices in a three-dimensional boundary layer

On the spatio-temporal stability of primary and secondary crossflow vortices in a three-dimensional boundary layer

Transition mechanisms in a three-dimensional boundary-layer flow with pressure-gradient changeover

Evolution of localized artificial disturbance in 2D and 3D supersonic boundary layers

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