Free-stream turbulence effects on transition within a laminar separation bubble

Istvan, Mark S.; Yarusevych, Serhiy

doi:10.2514/6.2017-3646

Cited by 4 publications

(4 citation statements)

References 38 publications

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“…The location past the “dead-air region,” where Cp is a maximum (the pressure gradient is almost negligible), is identified as the reattachment point. 6–9 In this figure, a separation bubble is indicated by a plateau followed by a steep rise in the pressure recovery region. Laminar to turbulent transition starts at the end of the plateau region.…”

Section: Surface Pressurementioning

confidence: 95%

“…It was shown that the overall development of the whole flow strongly depends on the outer region of the turbulent part rather than the inner layer. The stability of the shear layer over the NACA 0018 airfoil for an α of 4° was studied by Boutilier and Yarusevych 8 and Istvan Yarusevych 9 using flow visualization and surface pressure fluctuations for an Re of 1 × 10 5 . Apart from the time-averaged features of the bubble, the convection speed inside the bubble was also reported that compares with the growing disturbances (30%–50% of the edge velocity) in the shear layer.…”

Section: Topology Of Laminar Separation Bubblementioning

confidence: 99%

“…Upstream of model blend point, the flow acceleration comes to an end, where the value of Cp is also minimum, indicating a suction peak. 1,9 Hereafter, this point is designated as Cpmin. Subsequent to Cpmin, the flow starts to decelerate as it slowly experiences an adverse pressure gradient.…”

Section: Surface Pressurementioning

confidence: 99%

“…Downstream to reattachment, δ increases steeply in the turbulent region and reaches a maximum near x/c=0.16, where the turbulent boundary layer attains its canonical form. Figure 9(b) and (c) shows the variation of surface pressure and skin friction coefficient (Cf=τw/0.5 ρue2 , where τw is the wall shear stress and ue being the velocity at the edge of the boundary layer) computed from PIV data obtained along the chord. The onset of separation and reattachment locations are identified, where Cf becomes zero.…”

Section: Mean Flow Characteristicsmentioning

confidence: 99%

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Characteristics of a separated flow past a semicircular leading-edge airfoil model under different imposed pressure gradient

Anand

Ganesh

2021

Proceedings of the Institution of Mechanical Engineers, Part G:

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The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

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