The Unsteady Boundary Layer in a Shock Tube

Deckker, B. E. L.; Weekes, M. E.

doi:10.1243/pime_proc_1976_190_031_02

Cited by 5 publications

(3 citation statements)

References 7 publications

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“…There is now considerable evidence for the presence of organized structures in supersonic flows. For example, Head & Bandyopadhyay (1981) found support for their hairpin vortex hypothesis from the schlieren photographs of Deckker & Weekes (1976) and Deckker (1980) in supersonic boundary layers. While the photographs do not contain incontrovertible evidence of hairpin vortices, the boundary layers are shown to contain coherent density structures inclined at about 45" to the wall.…”

Section: Introductionmentioning

confidence: 90%

On the structure of high-Reynolds-number supersonic turbulent boundary layers

1991

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Experimental results are presented that reveal key features of the large-scale organized structures in a supersonic, turbulent boundary layer. Measurements were obtained in a Mach 3 zero-pressure-gradient boundary layer using a crossed-wire probe and arrays of normal hot wires with vertical, spanwise, and streamwise separations ranging from 0.1 to 0.6δ. Space–time correlation results indicate the existence of large-scale structures of a size comparable to δ, with a spanwise extent only slightly less than the vertical scale. The convection velocity of the large-scale motions is nearly constant across 80% of the boundary layer and is equal to approximately 0.9U∞.It is shown that positive events detected with the VITA conditional sampling technique correspond to steep gradients in the streamwise mass flux which extend across most of the boundary layer. These sharp gradients appear to be the upstream interfaces of large-scale turbulent ‘bulges’, similar to those seen in incompressible boundary layers. In a reference frame moving with the convection speed of the sharp gradients, low-momentum fluid is observed rotating on a large-scale, while high-momentum fluid forms a saddle point on the upstream edge of the large-scale motion. These motions are associated with elevated levels of the shear product, emphasizing their role in the dynamics of the boundary layer.

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Section: Introductionmentioning

confidence: 90%

On the structure of high-Reynolds-number supersonic turbulent boundary layers

1991

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“…More direct evidence in favour of the hairpin-vortex hypothesis comes from the experiments of Prof. Deckker, where the focused schlieren technique was used in a rectangular duct, to make visible the growth of the boundary layer following the passage of a shock. The paper by Deckker & Weekes (1976) shows spark photographs of the flow on the floor of the duct for two different strengths of shock wave, with different time intervals following the passage of the shock. Where the boundary layer is turbulent, as in the photographs reproduced here as figures 41 (a, b ) , quite marked and regular striations are visible in the flow close to the wall.…”

Section: Additional Observationsmentioning

confidence: 99%

New aspects of turbulent boundary-layer structure

1981

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Flow visualization studies of the zero-pressure-gradient turbulent boundary layer over the Reynolds-number range 500 < Reθ < 17500 have shown large Reynolds-number effects on boundary-layer structure.At high Reynolds numbers (Reθ > 2000, say) the layer appears to consist very largely of elongated hairpin vortices or vortex pairs, originating in the wall region and extending through a large part of the boundary-layer thickness or beyond it; they are for the most part inclined to the wall at a characteristic angle in the region of 40–50°. Large-scale features, which exhibit a slow overturning motion, appear to consist mainly of random arrays of such hairpin vortices, although there is some evidence of more systematic structures.At low Reynolds numbers (Reθ < 800, say) the hairpin vortices are very much less elongated and are better described as horseshoe vortices or vortex loops; large-scale features now consist simply of isolated vortex loops (at the very lowest Reynolds numbers), or of several such loops interacting strongly, and show a relatively brisk rate of rotation.

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“…Some evidence also exists for the presence of coherent motions in supersonic flows. For example, the schlieren photographs of Deckker & Weekes (1976) and Deckker (1980) show the floor of a duct after the passage of a shock wave (see Head & Bandyopadhyay 1981). For two different shock strengths, 45" striations were visible close to the wall.…”

Section: Introductionmentioning

confidence: 99%

Organized structures in a compressible, turbulent boundary layer

1987

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Experimental results are presented that show the existence of organized structures in a compressible, turbulent boundary layer. Results were obtained using arrays of hot wires and wall pressure transducers in a Mach-3 zero-pressure-gradient boundary layer. The VITA method of conditional sampling was used to deduce average pressure events at the wall and mass flux events throughout the boundary layer; these results show qualitative similarity to those found in incompressible flows. By conditioning upon the middle hot wire from a three-wire probe, evidence is found suggesting that structures exist of a height comparable with the boundary-layer thickness. Furthermore, two-point conditional sampling was used to show that an average pressure event could be extracted by conditioning upon mass-flux events. From this procedure we found that the structures maintain their shape as they travel downstream and also that their spanwise extent is very limited.The inferred angle from correlations between two hot wires, and between a hot wire and a wall-pressure transducer, indicate that the average structure is inclined at approximately 45° for a large part of the boundary layer. This result agrees well with structures observed in schlieren photographs of supersonic boundary layers. Measurements of the instantaneous angle show a wide distribution of structure angles, and the general behaviour of the large-scale structures is consistent with the hairpin loop model of wall turbulence.

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The Unsteady Boundary Layer in a Shock Tube

Cited by 5 publications

References 7 publications

On the structure of high-Reynolds-number supersonic turbulent boundary layers

On the structure of high-Reynolds-number supersonic turbulent boundary layers

New aspects of turbulent boundary-layer structure

Organized structures in a compressible, turbulent boundary layer

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