Effects of flow width in nominally two-dimensional turbulent separated flows

Ciampoli, Fabio; Hancock, P. E.

doi:10.1007/s00348-005-0050-4

Cited by 6 publications

(4 citation statements)

References 10 publications

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“…Nevertheless, it should be emphasized that the average flow near the centreline is not necessarily the same as the flow that would be obtained if the test-section width was infinite. In a geometry-induced TSB created with a fence and splitter plate, Ciampoli & Hancock (2006) found that residual effects of the tunnel sidewalls are seen in the mean wall shear stress near the tunnel centreline up to a test-section width to bubble length ratio of approximately 7. This is much larger than any experiment performed so far on pressure-induced TSBs (see table 1, where is typically of the order of one).…”

Section: Resultsmentioning

confidence: 99%

Measurements of pressure and velocity fluctuations in a family of turbulent separation bubbles

et al. 2020

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Section: Resultsmentioning

confidence: 99%

Measurements of pressure and velocity fluctuations in a family of turbulent separation bubbles

et al. 2020

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“…The oil-film pattern shows a high level of three-dimensionality, which is not surprising given the value of the aspect ratio w/L b  1•3, where w = 0•6m is the width of the test section and L b = 0•46m is the length of the separation bubble as obtained from the distance between the two saddle points at z = 0. In a fence and splitter-plate flow, Ciampoli and Hancock (11) found that residual effects of the tunnel side walls are seen in the mean wall shear stress near the tunnel centreline up to w/L b  7, although it should be noted that the fl ow near the surface is more strongly affected by the lateral pressure gradients caused by the side walls than the fl ow away from the test surface.…”

Section: Separated Flow Region: Oil-film Visualisationmentioning

confidence: 99%

A new wind tunnel for the study of pressure-induced separating and reattaching flows

et al. 2015

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The design, construction, and validation of a new academic wind tunnel is described in detail. The wind tunnel is of a classical, blow-down type and generates a pressure-induced, turbulent separation bubble on a flat test surface by a combination of adverse and favorable pressure gradients. The Reynolds number, based on momentum thickness just upstream of separation, is Re θ  5,000 at a free-stream velocity of U ref = 25ms -1 . The length of the separation bubble is estimated at 0·42 ± 0·02m by three different methods. Results of a numerical simulation demonstrate the absence of flow separation in the wind-tunnel contraction. This results in a turbulence level of about 0·05% in the test section. Oil-film visualisation experiments show that the flow near the wall is strongly three-dimensional in the recirculating region and that the topology of the limiting streamlines is consistent with experiments performed on configurations with fixed separation. Finally, spatial variations of the forward-flow fraction have been documented using a thermal-tuft probe and are shown to compare well with the results of the oil-film visualisation.

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“…'End effects' are largest near the surface, where residual lateral pressure gradients formed in the flow above exert their influence. The more recent study of Ciampoli & Hancock (2006), indicates (assuming the side-by-side equivalence) that the largest residual influence will have been in the mean wall shear stress, with an error of +2 %. The large eddy simulation by di Mare & Jones (2003), assuming spanwise invariance, and its good agreement with the present measurements regarded as spanwise invariant, namely those at z = 380 mm (see later), adds further support that the flow width was adequate.…”

Section: Flow Rig and Measurements Techniquesmentioning

confidence: 99%

“…The present flow is in the class of sharp-edge separation, with a very thin laminar boundary layer upstream of the separation line, formed by a bluff body. Its specific coplanar, two-dimensional counterparts have been studied in detail by Ruderich & Fernholz (1986), Castro & Haque (1987), Jaroch & Fernholz (1989), Hancock (2000) and Ciampoli & Hancock (2006), where the last work revisited the issue of the conditions necessary for negligible end effects. In these studies the separated flow was strong in Fernholz' classification (Fernholz 1994).…”

Section: Introductionmentioning

confidence: 99%

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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Effects of flow width in nominally two-dimensional turbulent separated flows

Cited by 6 publications

References 10 publications

Measurements of pressure and velocity fluctuations in a family of turbulent separation bubbles

Measurements of pressure and velocity fluctuations in a family of turbulent separation bubbles

A new wind tunnel for the study of pressure-induced separating and reattaching flows

Moderately three-dimensional separated and reattaching turbulent flow

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