Boundary layer development after a region of three-dimensional separated flow

Chun-xiao, Cao; Hancock, P. E.

doi:10.1016/j.euromechflu.2003.10.016

Cited by 3 publications

(3 citation statements)

References 22 publications

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“…The idea of using spanwise-invariant regions stemmed from other work which exhibited spanwise-invariance provided the flow width was large enough for end effects to have become negligible. These other sources include Sutton, Devenport & Barkey Wolf (1991) and Hancock & McCluskey (1996), and also confirmed in the work of Cao (2002) and Cao & Hancock (2004). Thus, it is expected that had the present flow been made wider still, all else constant, the extent of the region of spanwise invariance would also have been wider.…”

Section: Introductionsupporting

confidence: 64%

“…For a more detailed discussion for streamline topology see Perry & Fairlie (1974). Cao (2002) and Cao & Hancock (2004) investigated the same type flow as that here, except that the separation lines were swept at larger angles, of ±25 • (and that it was formed on a bluff thick plate). The purpose of that work was to study the flow as it developed to distances well downstream of reattachment, the bluff plate providing an easy way to generate the smaller separation bubble needed to obtain the required relative development distance in the wind tunnel used.…”

Section: Introductionmentioning

confidence: 98%

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Moderately three-dimensional separated and reattaching turbulent flow

Hardman

Hancock

2010

J. Fluid Mech.

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A fully three-dimensional turbulent separated flow was set up such that it had a systematic link to two-dimensional flow, as a way of investigating the more complicated nature of this flow type. The central region of the flow was fully three-dimensional, but was bounded on its sides by regions of ‘spanwise invariance’ in which the flow was invariant in the lateral direction, or very nearly so. A special case of spanwise invariance, which is statistically two-dimensional, is one in which the streamlines are also coplanar, or at least nominally so in numerous experimental studies. Another aspect of the present arrangement is that the side regions should ideally provide well-defined boundary conditions. The separation was formed downstream of a doubly swept normal flat plate, forming a ‘v’-shaped separation line, mounted on the front of a splitter plate, mounted in the centre of the wind tunnel working section. The predominantly inward flow to the central region implies a negative lateral strain rate (∂W/∂z), but all nine strain rates are non-zero. Measurements were made using pulsed-wire anemometry techniques for mean velocities, Reynolds stresses and wall shear stress. Even though the sweep angle is mild at ±10°, the effect is to increase the bubble height by over 50% in its centre to create a ‘bulge’, symmetrical about the centreline. The degree of three-dimensionality is described as moderate in that the peak inflow velocity from the side regions is less than 0.2 of the free-stream velocity, but comparable with the peak in the reverse-flow velocity. A larger sweep angle would give a larger inflow velocity. A separate study (Cao & Hancock, Eur. J. Mech. B/Fluids, vol. 23, 2004, p. 519) has shown that the bulge persists very far downstream, so that accurate physical modelling of the separated region is likely to be important in modelling the flow well downstream. An intermediate region exists between the invariant side region and the bulge, where all the stress levels are reduced, as would be expected from the effects of streamline convergence. Although overall there is a flow inward to the centre (streamline convergence), part of the overlying shear layer is subjected to diverging flow and an intensification of Reynolds stresses near the centre of the bulge.

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Section: Introductionsupporting

confidence: 64%

Section: Introductionmentioning

confidence: 98%

Moderately three-dimensional separated and reattaching turbulent flow

Hardman

Hancock

2010

J. Fluid Mech.

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“…Numerical simulations of the surface streamlines over the MVG show that they spill over the slant edges. (For an analogous flow of separation from a chevron-shaped backward-facing step, see [37]. The slant edge is literally a separation line in what Tobak and Peake, 30 following Wang, 22 calls a local separation line.…”

Section: B Surface Flow At the Mvg Sidementioning

confidence: 99%

Experimental and Numerical Study of Flow Topology Past Micro-Vortex Generators

Pierce

Shih

et al. 2010

40th Fluid Dynamics Conference and Exhibit

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Detailed experimental and numerical visualizations of the flow past a micro vortex generator (MVG) in the form of a ramp with swept sides in a Mach 2.5 flow revealed a complex near-field topology. The incoming flow separated over the leading edge of the MVG despite the ramp angle being below the threshold for incipient separation. The separation over the MVG protuberance produced a weak trailing horseshoe vortex system. The attachment line shows a saddle/foci combination on each side of a nodal point of attachment. The flow over the top of the MVG separated off the slant edges to produce a large primary vortex pair. This large primary vortex pair induced two secondary vortex filament pairs, one off the top of the MVG and another at the corner of the MVG with the flat plate. Extra complexities were revealed at the trailing edge with at least two pairs of saddle/foci combinations observed. It is postulated that vortex filaments spring from the various saddle/foci combinations as these were not observed experimentally or computationally. Symmetry breaking due to flow unsteadiness was also observed in the MVG wake.

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Measurements of Flows Over Isolated Valleys

Garvey

Castro

Wiggs

et al. 2005

Boundary-Layer Meteorol

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Abstract. Wind tunnel measurements of the flow over an isolated valley both normal and at an angle (45 o ) to a simulated neutrally stable atmospheric boundary layer are presented. Attention is concentrated on the nature of the near-surface flow upwind and downwind of the valley and the character of the flow within the valley itself. The work formed part of a wider study which included detailed field measurements around an African desert valley and some limited comparisons with that work are included. A scale of about 1:1000 was used for the laboratory work, in which an appropriate combination of hot wire and particle image velocimetry was employed. For a valley normal to the upwind flow, it is shown that the upstream influence of the valley extends to a distance of at least one half of the axial valley width upstream of the leading edge, whereas differences in mean flow and turbulence could be identified well beyond two valley widths from the downwind edge. Nonnormal wind angles lead to significant along-valley flows within the valley and, even at two valley heights above the valley ridge level, there remains a significant spanwise flow component. Downwind turbulence levels are somewhat lower in this case, but are still considerably higher than in the undisturbed boundary layer. At both flow angles, there are significant recirculation regions within the valleys, starting from mean separation just beyond the leading edge, but the strong spanwise flow in the 45 o case reduces the axial extent of the separated zone. The flow is shown to be in some ways analogous to flow over an isolated hill. Our results usefully enhance the field data and could be used to improve modelling of saltation processes in the field.

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Boundary layer development after a region of three-dimensional separated flow

Cited by 3 publications

References 22 publications

Moderately three-dimensional separated and reattaching turbulent flow

Moderately three-dimensional separated and reattaching turbulent flow

Experimental and Numerical Study of Flow Topology Past Micro-Vortex Generators

Measurements of Flows Over Isolated Valleys

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