Turbulence measurements around a mild separation bubble and downstream of reattachment

Alving, Amy E.; Fernholz, H. H.

doi:10.1017/s0022112096002807

Cited by 68 publications

(53 citation statements)

References 17 publications

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“…5), which is in agreement with the enhancement of the Reynolds stresses downstream of a laminar separation, as reported by Castro and Epik (1998). Moreover, the order of magnitudes of the Reynolds stresses is consistent with results obtained just behind a turbulent separation (Alving and Fernholz 1996). The fact that the overall level of each Reynolds stress is higher than expected for a canonical turbulent boundary layer, and that these levels are still decreasing at the downstream edge of the measurement domain (x/d 0 = 28), indicates that the boundary layer remains affected by the trip at least up to there.…”

Section: Reynolds Stressessupporting

confidence: 91%

Tomographic-PIV measurement of the flow around a zigzag boundary layer trip

Elsinga

Westerweel

2011

Exp Fluids

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Tomographic-PIV was used to measure the boundary layer transition forced by a zigzag trip. The resulting instantaneous three-dimensional velocity distributions are used to quantitatively visualize the flow structures. They reveal undulating spanwise vortices directly behind the trip, which break up into individual arches and then develop into the hairpin-like structures typical of wallbounded turbulence. Compared to the instantaneous flow structure, the structure of the average velocity field is very different showing streamwise vortices. Such streamwise vortices are often associated with the low-speed streaks occurring in bypass transition flows, but in this case clearly are an artifact of the averaging. Rather, the present streaks in the separated flow region directly behind the trip are resulting from the waviness in the spanwise vortices as introduced by the zigzag trip. Furthermore, these streaks and the separated flow region are observed to be related to a large-scale, spanwise uniform unsteadiness in the flow that contributes significantly to the velocity fluctuations over large downstream distances (up to at least the edge of the present measurement domain).

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Section: Reynolds Stressessupporting

confidence: 91%

Tomographic-PIV measurement of the flow around a zigzag boundary layer trip

Elsinga

Westerweel

2011

Exp Fluids

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“…Similarly to the present study, Alving and Fernholz (1996) concluded that the relaxation process is controlled by the outer energetic motions (wake-driven) in a way that it is not usually seen in canonical boundary layers, whose growth can be described by the wall-driven mechanism.…”

Section: Revisiting Some Literaturesupporting

confidence: 85%

“…Two further studies in which there are no trips involved are Alving and Fernholz (1996) and Castro and Epik (1998) who studied the boundary layer formed downstream of a recirculation bubble. This recirculation was generated by an adverse pressure and a blunt trailing edge respectively.…”

Section: Revisiting Some Literaturementioning

confidence: 99%

Near field development of artificially generated high Reynolds number turbulent boundary layers

2016

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Particle image velocimetry (PIV) is conducted in the near field of two distinct wall-mounted trips for the artificial generation of a high Reynolds number turbulent boundary layer. The first of these trips consists of high aspect ratio obstacles which are supposed to minimize the influence of their wakes on the near-wall region, contrasting with low aspect ratio trips which would enhance this influence.A comprehensive study involving flow description, turbulent/non-turbulent interface detection, a low order model description of the flow and an exploration of the influence of the wake in the near-wall region is conducted and two different mechanisms are clearly identified and described. First, high aspect ratio trips generate a wall-driven mechanism whose characteristics are: a thinner, sharper and less tortuous turbulent/non-turbulent interface and a reduced influence of the trips' wake in the near-wall region. Second, low aspect ratio trips generate a wake-driven mechanisms in which their turbulent/nonturbulent interface is thicker, less sharply defined and with a higher tortuosity and the detached wake of the obstacles presents a significant influence on the near-wall region. Study of the low order modelling of the flow field suggests that these two mechanisms may not be exclusive to the particular geometries tested in the present study but, on the contrary, can be explained based on the predominant flow features. In particular, the distinction of these two mechanisms can explain some of the trends that have appeared in the literature in the past decades.

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“…On the contrary, shed vortices with vorticity in z, i.e. the recirculation-like structures present for the Saw case and also reported in Alving and Fernholz (1996) and Castro and Epik (1998), would enhance the wake influence on the wall generating a wake-driven mechanism.…”

Section: Discussionmentioning

confidence: 70%

“…These trips with non-uniform blockage create a distorted wake which, after an adaptation region, may influence the formation of the inner structures up to a larger extent than in the former case, where the inner structures may not be as disturbed due to the low blockage at y = 0. This influence of the wake in the near-wall region has also been reported as a characteristic of re-attached flows downstream of a separation (Alving and Fernholz 1996;Castro and Epik 1998). Different heights and degrees of immersion in the boundary layer are tested in order to assess the influence of these parameters on the recovery length for canonical properties of the generated boundary layer.…”

Section: Introductionmentioning

confidence: 86%

On the Formation Mechanisms of Artificially Generated High Reynolds Number Turbulent Boundary Layers

Rodríguez-López

Bruce

Buxton

2016

Boundary-Layer Meteorol

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We investigate the evolution of an artificially thick turbulent boundary layer generated by two families of small obstacles (divided into uniform and non-uniform wall normal distributions of blockage). One-and two-point velocity measurements using constant temperature anemometry show that the canonical behaviour of a boundary layer is recovered after an adaptation region downstream of the trips presenting 150% higher momentum thickness (or equivalently, Reynolds number) than the natural case for the same downstream distance (x ≈ 3 m). The effect of the degree of immersion of the obstacles for h/δ 1 is shown to play a secondary role. The one-point diagnostic quantities used to assess the degree of recovery of the canonical properties are the friction coefficient (representative of the inner motions), the shape factor and wake parameter (representative of the wake regions); they provide a severe test to be applied to artificially generated boundary layers. Simultaneous two-point velocity measurements of both spanwise and wall-normal correlations and the modulation of inner velocity by the outer structures show that there are two different formation mechanisms for the boundary layer. The trips with high aspect ratio and uniform distributed blockage leave the inner motions of the boundary layer relatively undisturbed, which subsequently drive the mixing of the obstacles' wake with the wall-bounded flow (wall-driven). In contrast, the low aspect-ratio trips with non-uniform blockage destroy the inner structures, which are then re-formed further downstream under the influence of the wake of the obstacles (wake-driven).

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Turbulence measurements around a mild separation bubble and downstream of reattachment

Cited by 68 publications

References 17 publications

Tomographic-PIV measurement of the flow around a zigzag boundary layer trip

Tomographic-PIV measurement of the flow around a zigzag boundary layer trip

Near field development of artificially generated high Reynolds number turbulent boundary layers

On the Formation Mechanisms of Artificially Generated High Reynolds Number Turbulent Boundary Layers

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