Evolution of isolated streamwise vortices in the late stages of boundary layer transition

Manu, K. V.; Mathew, Joseph; Dey, J.

doi:10.1007/s00348-009-0747-x

Cited by 7 publications

(17 citation statements)

References 17 publications

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“…The mechanism of the formation of an isolated streamwise vortex downstream of the hill has been described before [23]. The half-span configuration generates streamwise vorticity by tilting of the spanwise vorticity of the boundary layer and by viscous generation at the wall due to the cross-stream pressure gradient.…”

Section: Description Of Experimentsmentioning

confidence: 99%

“…The half-span configuration generates streamwise vorticity by tilting of the spanwise vorticity of the boundary layer and by viscous generation at the wall due to the cross-stream pressure gradient. The dominant flow structure downstream of the hill is a single, streamwise vortex whose size is of the order of the hill height h; this flow development was examined with a laminar flow simulation of the vicinity of the hill [23], and is shown in Fig. 2.…”

Section: Description Of Experimentsmentioning

confidence: 99%

“…Here, measurements were taken within one and a half hours between calibrations. Details of the PIV unit (double cavity Nd:YAG laser, a CCD camera (sharpVISION 1400DE; 1360 Â 1036 pixel resolution), and measurements have been reported before [23,21]. The data processing software was based on a second-order accurate mesh-free algorithm [19], with an estimated average error in particle displacement of 1.2% in streamwise and less in the other directions in a 3-d measurement.…”

Section: Description Of Experimentsmentioning

confidence: 99%

“…It was an important demonstration because, in prior studies with flows that underwent transition, inflections in upstream profiles were supposed to have provoked the transition. Recently, this work was extended to flat plate boundary layers [23]. There are no other studies with isolated streamwise vortices.…”

Section: Introductionmentioning

confidence: 98%

“…Here we present analyses of the transition process for the steep hill case (mean slope of 1:10) from Manu et al [23]. Transition occurred only when the freestream velocity exceeded a threshold, even though, in every case, the streamwise vortices made the boundary layer velocity profiles inflectional.…”

Section: Introductionmentioning

confidence: 98%

See 4 more Smart Citations

Local structure of boundary layer transition in experiments with a single streamwise vortex

Manu

Dey

Mathew

2015

Experimental Thermal and Fluid Science

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Section: Description Of Experimentsmentioning

confidence: 99%

Section: Description Of Experimentsmentioning

confidence: 99%

Section: Description Of Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

See 3 more Smart Citations

Local structure of boundary layer transition in experiments with a single streamwise vortex

Manu

Dey

Mathew

2015

Experimental Thermal and Fluid Science

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Boundary layer transition experiments with embedded streamwise vortices

2018

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Experiments were conducted with a counter-rotating, streamwise vortex pair embedded in flat plate boundary layers, in a low-turbulence wind tunnel, to understand the role of local separation on transition. Steady, streamwise vortices were generated downstream of gaps in spanwise-uniform, smooth hills (of height h) affixed to the plate, 175 mm from its leading edge. The flow between is directed away from the plate. At the four tunnel speeds 1.8-3.5 m/s considered, the Reynolds numbers based on displacement thickness at this location varied from 248 to 346. Small, medium and large gaps of 2, 4 and 8 mm, respectively, were set up; they were about a third to twice the boundary layer thickness (2=3\b=h\8=3). With the closest vortex pairs, transition was observed at all freestream speeds considered. With larger spacing, transition occurred at the highest speed only. The vortex pair caused the flow to separate in all but the largest-gap cases. Separation was steady and reattachment unsteady in all cases. Velocity fluctuations grew slightly upstream of re-attachment in transitional cases. No evidence was found for separation or re-attachment as a direct cause for transition; transition occurred even without separation. Instead, whenever transition was observed, its origin could be traced to instability of a streak of sufficient amplitude that had been created by the vortex pair. Streak instability appeared as fluctuations growing along its sides and spreading. Anomalous behaviour was also observed with moderate spacing, where transition did not occur in spite of flow separation and streak amplitudes in excess of known thresholds for streak instability.

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Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element

2015

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Streamwise streaks, their lift-up and streak instability are integral to the bypass transition process. An experimental study has been carried out to find the effect of a mesh placed normal to the flow and at different wall-normal locations in the late stages of two transitional flows induced by free-stream turbulence (FST) and an isolated roughness element. The mesh causes an approximately 30 % reduction in the free-stream velocity, and mild acceleration, irrespective of its wall-normal location. Interestingly, when located near the wall, the mesh suppresses several transitional events leading to transition delay over a large downstream distance. The transition delay is found to be mainly caused by suppression of the lift-up of the high-shear layer and its distortion, along with modification of the spanwise streaky structure to an orderly one. However, with the mesh well away from the wall, the lifted-up shear layer remains largely unaffected, and the downstream boundary layer velocity profile develops an overshoot which is found to follow a plane mixing layer type profile up to the free stream. Reynolds stresses, and the size and strength of vortices increase in this mixing layer region. This high-intensity disturbance can possibly enhance transition of the accelerated flow far downstream, although a reduction in streamwise turbulence intensity occurs over a short distance downstream of the mesh. However, the shape of the large-scale streamwise structure in the wall-normal plane is found to be more or less the same as that without the mesh.

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Evolution of isolated streamwise vortices in the late stages of boundary layer transition

Cited by 7 publications

References 17 publications

Local structure of boundary layer transition in experiments with a single streamwise vortex

Local structure of boundary layer transition in experiments with a single streamwise vortex

Boundary layer transition experiments with embedded streamwise vortices

Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element

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