Effects of freestream turbulence on the secondary instability of the roughness-induced crossflow vortex in swept flat plate boundary layers

Nakagawa, Kosuke; Ishida, Takahiro; Tsukahara, Takahiro

doi:10.1016/j.ijheatfluidflow.2023.109161

Cited by 4 publications

(11 citation statements)

References 42 publications

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“…Similar results were obtained by recent DNSs on wing surfaces (Faúndez Alarcón et al, 2022) and on a flat plate (Mamidala et al, 2022). Nakagawa et al (2023a) also reported the wavelength dependency in the swept flat plate boundary layer. They found that, in the long-wavelength FST condition, the turbulent transition position was shifted upstream compared to the short-wavelength FST condition because the traveling CFV was induced upstream.…”

Section: Introductionsupporting

confidence: 89%

“…After that, we discuss causes of individual transition process changes between two paths in § 3.2-3.4. In § 3.5, we summarize the transition process dependency on the FST wavelength, based on the present and previous studies (Brynjell-Rahkola et al, 2017;Ishida et al, 2022a;Nakagawa et al, 2023a).…”

Section: Resultsmentioning

confidence: 99%

“…Reynolds number is defined as Re = U 0 δ * 0 /ν = 337.9, where U 0 and δ * 0 are respectively the external chordwise velocity and the displacement thickness at the inlet, and ν is the kinematic viscosity. Regarding the parameters related to the FSC flow, m is the acceleration coefficient and φ is the streamline angle at the inlet, which were set at the same values with those in previous studies (Högberg and Henningson, 1998;Brynjell-Rahkola et al, 2017;Nakagawa et al, 2023a). The chordwise length L x was adjusted to capture the laminar-to-turbulent transition in the cases tested here.…”

Section: Methodsmentioning

confidence: 99%

“…Recent investigations of the dependency of the CFV turbulence transition process have focused on the effects of the FST intensity on the amplitude of SIs (Downs and White, 2013) and the turbulent transition position ( Örlü et al, 2021;Vincentiis et al, 2022). The SIs were classified high-frequency Type-1 SI and Type-2 SI under non-FST conditions, whereas low-frequency Type-3 SI was reported under with-FST conditions (Högberg and Henningson, 1998;Malik et al, 1999;White and Saric, 2005;Serpieri and Kotsonis, 2016;Nakagawa et al, 2023a). The effect of unsteady fluctuations on the turbulent transition process is that they affect the wake structure of the roughness, resulting in a turbulent transition without CFV formation despite the low roughness height.…”

Section: Introductionmentioning

confidence: 99%

“…In the turbulent transition process on the swept flat plate under the non-FST condition, a turbulent transition due to a hairpin vortex occurs above a roughness Reynolds number of Re kk ≈ 700 (based on roughness height and base flow velocity on the top of roughness, and definition is described in § 2) (Brynjell-Rahkola et al, 2017;Ishida et al, 2022a;Nakagawa et al, 2023b). This threshold is reduced to Re kk ≈ 300 by the presence of FST (Nakagawa et al, 2023a). Also for swept wings, both numerical and experimental studies ( Örlü et al, 2021;Vincentiis et al, 2022) have reported hairpin vortex transitions at low roughness height due to the effect of the FST.…”

Section: Introductionmentioning

confidence: 99%

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Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Nakagawa,

Ishida,

Tsukahara

2024

Preprint

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Laminar-turbulent transitions in boundary layers are one of the major research topics in fluid dynamics.In this study, we focused on a three-dimensional boundary layer formed on a swept flat plate.In this boundary layer, the crossflow instability is dominant, and the instability induces crossflow vortices (CFVs).Many studies have focused on the dependency of the transition process on the intensities of steady or unsteady disturbances, which correspond to a roughness element and freestream turbulence (FST), respectively.On the other hand, the effects of the FST wavelength are still unclear.Moreover, there is a lack of knowledge about the transition processes caused by both steady and unsteady disturbances.We investigated how the transition process of a stationary structure caused by cylindrical roughness changes depending on the FST wavelength using direct numerical simulations.We classified transition processes into two types: processes in which stationary structures grow into CFVs and processes in which hairpin vortices are generated on the stationary structures.The former is further classified into four types depending on the presence or absence of FST and on the FST wavelength.We revealed the contributions of different FST wavelengths to the transition process changes.The short-wavelength FST provides hairpin vortices to the stationary structure at low roughness height conditions because of its high-frequency components.The long-wavelength FST changes the process due to unsteady fluctuations influencing the stationary structure.In summary, depending on the FST wavelength, the transition process is changed by a completely different mechanism.

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Section: Introductionsupporting

confidence: 89%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Nakagawa,

Ishida,

Tsukahara

2024

Preprint

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Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Nakagawa,

Ishida,

Tsukahara

2024

Flow Turbulence Combust

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Laminar-turbulent transitions in boundary layers are one of the major research topics in fluid dynamics. In this study, we focused on a three-dimensional boundary layer formed on a swept flat plate. In this boundary layer, the crossflow instability is dominant, and the instability induces crossflow vortices (CFVs). Many studies have focused on the dependency of the transition process on the intensities of steady or unsteady disturbances, which correspond to a roughness element and freestream turbulence (FST), respectively. On the other hand, the effects of the FST wavelength are still unclear. Moreover, there is a lack of knowledge about the transition processes caused by both steady and unsteady disturbances. We investigated how the transition process of a stationary structure caused by cylindrical roughness changes depending on the FST wavelength using direct numerical simulations. We classified transition processes into two types: processes in which stationary structures grow into CFVs and processes in which hairpin vortices are generated on the stationary structures. The former is further classified into four types depending on the presence or absence of FST and on the FST wavelength. We revealed the contributions of different FST wavelengths to the transition process changes. The short-wavelength FST provides hairpin vortices to the stationary structure at low roughness height conditions because of its high-frequency components. The long-wavelength FST changes the process due to unsteady fluctuations influencing the stationary structure. In summary, the transition processes undergo different mechanisms between short- and long-wavelength FST.

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Premature secondary instabilities induced by freestream turbulence in swept flat plate boundary layer

Nakagawa,

Ishida,

Tsukahara

2023

Proceeding of 10th International Symposium on Turbulence, Heat and Mass Transfer, THMT-23, Rome, Italy, 11-15 September 2023

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Effects of freestream turbulence on the secondary instability of the roughness-induced crossflow vortex in swept flat plate boundary layers

Cited by 4 publications

References 42 publications

Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Changes in the Transition Process of Roughness-Induced Crossflow Vortices due to Freestream Turbulence

Premature secondary instabilities induced by freestream turbulence in swept flat plate boundary layer

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