On the use of lagrangian variables in descriptions of unsteady boundary-layer separation

Cowley, Stephen J.; Dommelen, L. L. van; Lam, Shui T.

doi:10.1098/rsta.1990.0165

Cited by 46 publications

(19 citation statements)

References 64 publications

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“…As seen in figure 10(a), the flow leading up to this bursting event has the ingredients for unsteady boundary layer separation -significant negative velocity gradient in the stream direction along the line ω = 0. See, for example, Cowley, Van Dommelen & Lam (1990). The separation thus triggers rapid growth of the observed multipole vortex structure, which quickly pulls itself outside the boundary layer.…”

Section: Analysis Of Highest-resolution Resultsmentioning

confidence: 99%

Investigation of a drag reduction on a circular cylinder in rotary oscillation

Shiels

Leonard

2001

J. Fluid Mech.

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Drag reduction in two-dimensional flow over a circular cylinder, achieved using rotary oscillation, was investigated with computational simulations. In the experiments of Tokumaru & Dimotakis (1991), this mechanism was observed to yield up to 80% drag reduction at Re = 15 000 for certain ranges of frequency and amplitude of sinusoidal rotary oscillation. Simulations with a high-resolution viscous vortex method were carried out over a range of Reynolds numbers (150-15 000) to explore the effects of oscillatory rotational forcing. Significant drag reduction was observed for a rotational forcing which had been very effective in the experiments. The impact of the forcing is strongly Reynolds number dependent. The cylinder oscillation appears to trigger a distinctive shedding pattern which is related to the Reynolds number dependence of the drag reduction. It appears that the source of this unusual shedding pattern and associated drag reduction is vortex dynamics in the boundary layer initiated by the oscillatory cylinder rotation. The practical efficiency of the drag reduction procedure is also discussed.

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Section: Analysis Of Highest-resolution Resultsmentioning

confidence: 99%

Investigation of a drag reduction on a circular cylinder in rotary oscillation

Shiels

Leonard

2001

J. Fluid Mech.

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“…It may be noted that this form of G can also be obtained from an argument discussed by Van Dommelen (1981) which requires regularity in the Lagrangian solution for the streamwise particle positions x and velocities u (see also Cowley et al 1990). …”

Section: Form Of the Terminal Singularitymentioning

confidence: 99%

“…The terminal solution describes the flow in the immediate vicinity of the separation point in a reference frame moving with the fluid particle which becomes longitudinally compressed to zero thickness as t + t, (Van Dommelen 1981;Cowley et al 1990). This particle is located within the boundary layer along the zero-vorticity line in accordance with the MRS conditions.…”

Section: Properties Of the Terminal Solutionmentioning

confidence: 99%

“…Van Dommelen K . FK Cassel, F. T. Smith and J. D. A. Walker & Shen (1982) hypothesized that the solution for the streamwise particle positions in Lagrangian coordinates should remain regular up to the time of separation; therefore, a local Taylor series expansion for the solution of the momentum equation near the point of separation was constructed, and the solution of the continuity equation (which becomes singular) was represented as an asymptotic series (see also Cowley, Van Dommelen & Lam 1990). An alternative derivation due to Elliott et al (1983) reproduced the same structure in Eulerian coordinates; a brief summary of this approach follows.…”

Section: Form Of the Terminal Singularitymentioning

confidence: 99%

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The onset of instability in unsteady boundary-layer separation

1996

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The process of unsteady two-dimensional boundary-layer separation at high Reynolds number is considered. Solutions of the unsteady non-interactive boundary-layer equations are known to develop a generic separation singularity in regions where the pressure gradient is prescribed and adverse. As the boundary layer starts to separate from the surface, however, the external pressure distribution is altered through viscous-inviscid interaction just prior to the formation of the separation singularity; hitherto this has been referred to as the first interactive stage. A numerical solution of this stage is obtained here in Lagrangian coordinates. The solution is shown to exhibit a high-frequency inviscid instability resulting in an immediate finite-time breakdown of this stage. The presence of the instability is confirmed through a linear stability analysis. The implications for the theoretical description of unsteady boundary-layer separation are discussed, and it is suggested that the onset of interaction may occur much sooner than previously thought.

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“…Subsequent work has incorporated the influence of heat transfer with the new models and also to extend the theory into the hypersonic regimes. The theory described in He et al (1992) Recent advances in the theory of unsteady separation (Van Dommelen & Cowley, 1990;Cowley et al 1991) have suggested that when a three-dimensional boundary layer undergoes a process of unsteady separation from a surface, a generic structure develops in a high Reynolds number flow. It is suggested that the eruption takes the form of a sharply focussed tongue of fluid that moves rapidly away from the surface.…”

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confidence: 99%

Computational and Analytical Methods in Nonlinear Fluid Dynamics

Walker¹

1993

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On the use of lagrangian variables in descriptions of unsteady boundary-layer separation

Cited by 46 publications

References 64 publications

Investigation of a drag reduction on a circular cylinder in rotary oscillation

Investigation of a drag reduction on a circular cylinder in rotary oscillation

The onset of instability in unsteady boundary-layer separation

Computational and Analytical Methods in Nonlinear Fluid Dynamics

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