Effects of localized blowing on the turbulent boundary layer over 2D roughness

Hamed, Ali M.; Nye, C. E.

doi:10.1007/s00348-021-03261-0

Cited by 4 publications

(2 citation statements)

References 68 publications

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“…A wide range of rough surfaces have been investigated as outlined by these studies Devi et al, 2022;Flack & Schultz, 2014;Hamed et al, 2021;Kadivar et al, 2021;Nyantekyi-Kwakye et al, 2017;Vadlamani et al, 2018;Volino et al, 2009Volino et al, , 2011Y. Wu & Christensen, 2010).…”

Section: Introductionmentioning

confidence: 99%

Turbulent structures beneath semi-submerged simulated ice cover over smooth and rough bed in a shallow channel

Nyantekyi-Kwakye,

Saeedi

2024

Preprint

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The effect of bed roughness on shear layer separation and the structure of turbulence in a shallow channel is evaluated. A planar particle velocimetry system is used to conduct detailed instantaneous velocity measurements beneath the simulated ice cover. The results show that although surface roughness modifies near-wall turbulence, once shear layer separation occurs, it becomes the controlling parameter of turbulence for flow shallow channels. The instantaneous velocity field show elongated separated shear layer underneath the cover for flow over the smooth bed compared to the rough bed. For the current shallow channel, the bed roughness significantly reduced the size of the separation bubble at the undersurface of the cover. The instantaneous size of the separated bubble expands and contracts depicting intense shear layer flapping at the undersurface of the cover, and this is dominant for the smooth bed flow. Close to the leading edge of the cover, the instantaneous spanwise vorticity magnitude shows dominance of small-scale instabilities akin to the Kelvin-Helmholtz type instability at interface of the separated shear layer. The Q-criterion and swirling strength revealed that separation of the shear layer generated large-scale vortices of varying length scale when compared to the bed roughness. The bed roughness promotes near-wall turbulence with elevated levels of Reynolds stresses compared to the smooth bed. However, at the undersurface of the cover, the high levels of turbulence were controlled by the flow separation. Compared to the bed roughness, a wide range of integral length scales are estimated within the separated shear layer, which contributed significantly to the generation of Reynolds stresses.

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Section: Introductionmentioning

confidence: 99%

Turbulent structures beneath semi-submerged simulated ice cover over smooth and rough bed in a shallow channel

Nyantekyi-Kwakye,

Saeedi

2024

Preprint

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“…Their results indicated that the drag reduction effect of uniform blowing on the 2D rough wall is similar to that for a smooth wall, and the uniform blowing makes the rough wall aerodynamically smoother due to the reduction of pressure drag. Hamed et al [44] carried out an experiment to study the blowing effects on the turbulent boundary layer over 2D k-type roughness. 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.…”

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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