Experimental study of instability modes in a three-dimensional boundary layer

Mueller, Bernhard; Bippes, H.

doi:10.2514/6.1987-1336

Cited by 28 publications

(14 citation statements)

References 2 publications

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“…Earlier experiments by Arnal et al, 5 Poll, 6 Bippes and NitschkeKowsky, 7 Miiller and Bippes, 8 Dagenhart et al, 9 and Dagenhart and Saric 10 have shown that both stationary and traveling crossflow vortices are present within the three-dimensional boundary layers of swept-wing flows. These instabilities are spawned from inflections in the mean velocity profile and are prevalent in regions of favorable pressure gradients (i.e., near the leading edge).…”

Section: Introductionmentioning

confidence: 96%

Evolution of stationary crossflow vortices in boundary layers on swept wings

Joslin

1995

AIAA Journal

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The spatial evolution of crossflow-vortex disturbances in a laminar boundary layer on a swept wing is computed by the direct numerical simulation of the incompressible Navier-Stokes equations. A wall-normal velocity distribution of steady suction and blowing at the wing surface is used to generate a strip of equally spaced and periodic disturbances along the span. Three simulations are conducted to study the effect of initial amplitude on both the disturbance evolution and to provide a database for transition-onset prediction methods. As an example application, a theory for a transition model is compared with the direct numerical simulations data. In each simulation, the vortex disturbances first enter a chordwise region that can be described as linear growth; then, the individual disturbances coalesce downsteam and either superpose linearly or interact nonlinearly with adjacent modes; finally, the crossflow vortices enter a region that contains strong nonlinear interactions sufficient to generate inflectional velocity profiles. As the initial amplitude of the disturbance increases (roughness size increases), the length of the evolution to breakdown decreases. In the example application, the three simulations collapse onto a single curve, which is an intermittency correlation for a transition model.

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Section: Introductionmentioning

confidence: 96%

Evolution of stationary crossflow vortices in boundary layers on swept wings

Joslin

1995

AIAA Journal

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“…The situation is somewhat different in three-dimensional boundary layers, such as those over swept wings. In a low-disturbance environment it has been experimentally demonstrated [14][15][16] that stationary cross-flow vortices are preferentially excited and the location of their appearance is intimately tied to micron-sized roughness in the model; this correlation was investigated by Radeztsky et al [17] who found an increase in the transition Reynolds number with subsequent levels of polishing of the wall. Radeztsky et al also placed isolated roughness elements on their swept surface to find a dependence of the transition "point" on roughness location, dimensions and spanwise spacing of the elements.…”

Section: Introductionmentioning

confidence: 98%

Görtler vortices promoted by wall roughness

Bottaro

Zebib

1997

Fluid Dyn. Res.

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Numerical experiments are conducted to investigate spatially developing Grrtler vortices and the way in which wall roughness promotes their formation and growth. Several different types of walls are examined and their relative merits as vortex promoters assessed. The only disturbances of the flow are due to the rough wall; hence, at each downstream station the local field feels (1) the upstream flow distribution (produced by the upstream wall conditions) and ( 2) the local forcing at the wall. Rapid vortex formation and growth, like in the case of ribleted walls, can be qualitatively explained by the positive combination of these two effects; when the two influences on the local flow field compete, e.g. for randomly distributed wall roughness, the equations with the boundary conditions filter the disturbances over some streamwise length, function of the roughness amplitude, to create coherent patches of vorticity out of the random noise.These patches can then be amplified by the instability mechanism. If a thin rough strip is aligned along the span of an otherwise smooth wall to trip the boundary layer, the filtering region is shorter and growth of the vortices starts earlier. Also for the case of an isolated three-dimensional hump a rapid disturbance amplification is produced, but in this case the vortices remain confined and a very slow spanwise spreading of the perturbation occurs. In all naturally developing cases, where no specific wavelengths are explicitly favored, the average spanwise wavelengths computed are very close to those of largest growth from the linear stability theory.

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“…Stationary crossflow waves (v and w disturbances) are typically very weak; hence, analytical models have been based on linear theory. However, experiments often show evidence of strong nonlinear effects (Dagenhart et al 1989(Dagenhart et al , 1990Bippes & Nitschke-Kowsky 1990;Bippes et al 1991;Deyhle et al 1993;Reibert et al 1996). Because the wave fronts are fixed with respect to the model and are nearly aligned with the potential-flow direction (i.e., the wavenumber vector is nearly perpendicular to the local inviscid streamline), the weak (v , w ) motion of the wave convects O(1) streamwise momentum producing a strong u distortion in the streamwise boundary-layer profile.…”

Section: Introductionmentioning

confidence: 99%