Reynolds number effect on the response of a rough wall turbulent boundary layer to local wall suction

Ghanadi, Farzin; Djenidi, L.

doi:10.1017/jfm.2021.215

Cited by 5 publications

(3 citation statements)

References 43 publications

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“…The above observations suggest that the rough-wall TBL under PGs responds first to the roughness and then to the PGs; the closer to the wall, the more dominant is the roughness effect. This is consistent with the finding of Ghanadi & Djenidi (2021a), who showed that roughness prevents relaminarization downstream of a local wall suction (or equivalently strong local FPG). It is also worth noticing that the boundary layers in the present study are not fully developed and hence the values may change in scenarios where fully developed state is achieved.…”

Section: Discussionsupporting

confidence: 92%

“…In the present study, the value of the ratio u /U is approximately 0.3 at a distance y = k and decreases continuously as y increases, as shown in figure 13 reporting the distribution of u /U. Accordingly, we focus the spectral analysis on the region delimited y = k (the vertical line in figure 12) where the Taylor hypothesis is appropriate (further discussions on the Taylor hypothesis for the present rough-wall TBL can be found in Ghanadi & Djenidi (2021a)). Note that for clarity, the spectral analysis is carried out for location IV only; similar results are obtained for the other locations.…”

Section: Roughness Elementmentioning

confidence: 77%

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Study of a rough-wall turbulent boundary layer under pressure gradient

Ghanadi

Djenidi

2022

J. Fluid Mech.

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The behaviour of a fully rough-wall turbulent boundary layer subjected to different pressure gradients is investigated for different Reynolds numbers using hot-wire measurements. Mean velocity and velocity root-mean-square measurements indicate that the boundary layer remains in a self-preserving state regardless of the pressure gradient. However, different pressure gradients lead to different self-preservation states, as suggested by the lack of collapse of the velocity profile between the pressure gradient cases. The results also indicate that the roughness effect is more important than the pressure gradient; particularly, the closer the wall, the more dominant the roughness effect over the pressure gradient effect on the boundary layer. Finally, both spectral and proper orthogonal decomposition analyses applied to the hot-wire measurements indicate that the pressure gradient impacts predominantly the large-scale motion.

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Section: Discussionsupporting

confidence: 92%

Section: Roughness Elementmentioning

confidence: 77%

Study of a rough-wall turbulent boundary layer under pressure gradient

Ghanadi

Djenidi

2022

J. Fluid Mech.

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“…They found that the localized blowing results in an increase in the time-averaged streamwise velocity but a reduction in the maximum streamwise-averaged Reynolds shear stress and turbulent kinetic energy. Furthermore, Djenidi et al [45,46] experimentally investigated the wall suction effects on the rough-wall turbulent boundary layer. It was seen from the velocity spectra contour maps that the suction decreases the energy at all scales of motion across the boundary layer.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation on Backward-Injection Film Cooling with Upstream Ramps

et al. 2022

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The present study investigates the effects of upstream ramps on a backward-injection film cooling over a flat surface. Two ramp structures, referred to as a straight-wedge-shaped ramp (SWR) and sand-dune-shaped ramp (SDR), are considered under a series of blowing ratios ranging from M = 0.5 to M = 1.5. Regarding the backward injection, the key mechanism of upstream ramps on film cooling enhancement is suggested to be the enlargement of the horizontal scale of the separate wake vortices and the reduction of their normal dimension. When compared to the SDR, the SWR modifies the backward coolant injection well, such that a larger volume of coolant is suctioned and concentrated in the near-field region at the film-hole trailing edge. As a consequence, the SWR demonstrates a more pronounced enhancement in film cooling than the SDR in the backward-injection process, which is the opposite of the result for the forward-injection scheme. For the SWR, the backward injection provides a better film cooling effectiveness than the forward injection, regardless of blowing ratios. However, for the SDR, the backward injection could show a superior effect to the forward injection on film cooling enhancement, when the blowing ratio is beyond a critical blowing ratio. In the present SDR situation, the critical blowing ratio is identified to be M = 1.0.

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