Large-scale coherent motions in turbulent boundary layers under an adverse pressure gradient up to flow separation

Eich, Felix; Kähler, Christian J.

doi:10.1016/j.ijheatfluidflow.2020.108645

Cited by 8 publications

(9 citation statements)

References 28 publications

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“…The results show that the detachment point, x D ′ , does not correlate with the shear-layer flapping, y M ′ , and the TSB endpoint, x E ′ . This agrees with the previous observations that indicated the displacement of the detachment point are derived by the fluctuations of the upcoming TBL (Eich & Kähler 2020; Ma et al. 2020).…”

Section: The Breathing Motionsupporting

confidence: 93%

“…This separation line is oriented in the spanwise direction, but it undulates due to the intermittency of the separation location. The undulating pattern of the separation line is attributed to its interaction with the low- and high-speed structures of the incoming TBL (Eich & Kähler 2020; Ma et al. 2020).…”

Section: Turbulent Separation Bubblementioning

confidence: 99%

“…In the upstream TBL, the energetic flow motions have a high St l of approximately 4, which gradually reduces to 0.1 with increasing x/c . The reduction in the St l of the TBL fluctuations is attributed to the effect of the APG on the low- and high-speed structures (Skote & Henningson 2002; Lee & Sung 2009; Eich & Kähler 2020).

Figure 6.Contours of the pre-multiplied PSD of u along ( a ) y / δ 0 = 1.0, ( b ) the upper shear layer and ( c ) the lower shear layer.…”

Section: Unsteady Motionsmentioning

confidence: 99%

“…The effect of TBL structures on the separation front has been demonstrated by two recent investigations. Eich & Kähler (2020) demonstrated that large-scale motions of the incoming TBL modulate the separation line. By investigating the TSB of a flat plate, they showed that large high-speed motions within the incoming TBL push the separation location in the downstream direction while large low-speed motions result in an upstream displacement of the separation location.…”

Section: Introductionmentioning

confidence: 99%

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Unsteady motions in the turbulent separation bubble of a two-dimensional wing

Wang

Ghaemi²

2022

J. Fluid Mech.

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The unsteadiness of a turbulent separation bubble (TSB) formed close to the trailing edge of a two-dimensional wing was investigated using time-resolved particle image velocimetry. The angle of attack was set to 9.7° and the chord-based Reynolds number was 720 000. The TSB consisted of two shear layers and formed a triangular shape in the streamwise–wall-normal plane. The vertices of this triangle consisted of an intermittent detachment point, a fixed corner close to the airfoil trailing edge and an intermittent endpoint in the wake region. The velocity field had three energetic regions each with different Strouhal numbers (Stl): (a) an upstream turbulent boundary layer (TBL) with Stl = 0.1 to 4, (b) a TSB with Stl = 0.03 to 0.08 and (c) two shear layers with Stl = 0.4 to 0.8. The low-frequency motions in the TSB consisted of large zones of positive and negative streamwise velocity fluctuation that were several times wider than the large-scale structures of the upstream TBL. These zones forced an undulation of the separation line and were attributed to Görtler structures. They were also correlated with the velocity fluctuations between the two shear layers. The breathing motion of the TSB occurred at Stl = 0.05. This breathing correlated with the location of the TSB endpoint and the flapping of the upper shear layer. The detachment point of the TSB featured broad fluctuations and did not demonstrate a strong correlation with the breathing motion.

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Section: The Breathing Motionsupporting

confidence: 93%

Section: Turbulent Separation Bubblementioning

confidence: 99%

Figure 6.Contours of the pre-multiplied PSD of u along ( a ) y / δ 0 = 1.0, ( b ) the upper shear layer and ( c ) the lower shear layer.…”

Section: Unsteady Motionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Unsteady motions in the turbulent separation bubble of a two-dimensional wing

Wang

Ghaemi²

2022

J. Fluid Mech.

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“…In addition, the details of the transition from the fully attached to the partly and fully separated flow is widely unknown [19]. Recently however, using planar PIV techniques [20] investigated the interaction of incoming turbulent superstructures and a flow separation region/bubble. Using conditional statistics it was found that the superstructures shift the mean separation location either up-or downstream depending on the momentum of the superstructure.…”

Section: Introductionmentioning

confidence: 99%

Superstructures in turbulent boundary layers with pressure gradients

Bross

Eich

Schanz

et al. 2021

Proc Appl Math and Mech

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Large-scale coherent structures have been observed in various wall-bounded turbulent flows. In turbulent boundary layers, streamwise elongated regions of high-and low-momentum in the log-law layer that can extent up to several boundary layer thicknesses are often referred to as superstructures. These structures contain a relatively large portion of the layer's turbulent kinetic energy and have been shown to interact with the near-wall features. In the last few decades extensive research on zero-pressure gradient turbulent boundary layers has been done, however by comparison, the structural characteristics for adverse pressure gradient turbulent boundary layer flows are much less studied. Therefore, the three-dimensional dynamics of turbulent superstructures in a turbulent boundary layer flow is investigated in the Atmospheric Wind Tunnel Munich (AWM) measurement using a novel multi-camera 3D time-resolved Lagrangian particle tracking approach. In this study, the structural properties and dynamics of turbulent superstructures within a zero pressure gradient (ZPG) turbulent boundary layer at Reτ = 5000 or Re θ = 14 000 that then flows over a curved plate subjected to a favorable (FGP) and strong adverse (APG) pressure gradient, which eventually separates, is considered. It was found that while the average superstructure topology is modulated by decelerating flow in the APG when compared to the ZPG region the basic shape and pattern is preserved.

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Investigating the effect of bio‐convection, chemical reaction, and motile microorganisms on Prandtl hybrid nanofluid flow across a stretching sheet

Khan,

Thabet,

Abd‐Alla

et al. 2023

Z Angew Math Mech

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Due to extensive application in extruding plastic sheet processes, liquid film condensation, glass blowing, biopolymer cylinder coatings, paper manufacture, and other processes, the thermodynamical characteristics of non‐Newtonian fluids across stretched surfaces have acquired ubiquitous essence. Therefore, the present communication aims to openly elucidate Prandtl fluid flow characteristics produced by a stretching surface. In this analysis, a hybrid nanofluid (HNF) is considered by using pure water as a base fluid and two various nanomaterials (copper and Titanium dioxide) as nanoparticles in the characterization of heat transfer. Moreover, the goal of this investigation is to ascertain the heat transfer characteristics of a magnetohydrodynamic (MHD) Prandtl hybrid nanofluid (PHNF) model. Across the stretching sheet, this article interrogates the inclined MHD, chemical reaction, bio‐convection, linearly thermal radiation, and Darcy–Forchheimer (DF) effect in the attendance of porous medium of HNF. The modified Buongiorno model for nanofluids is adopted to explore heat transport augmentation. It includes the mechanics of nanoparticle random motion and thermo‐migration as well as useful nanofluid characteristics. Additionally, the outcomes are contrasted with nanofluid flow. With the right level of similarity, the process converts partial differential equations emerging in nanofluidic systems into nonlinear differential equation systems. The (FDM) finite difference approach (Lobatto IIIA) is used for the nonlinear nanofluid issue with the precision of order 4 to 5 and is implemented using a variety of collocation locations. The strength of (Lobatto IIIA) is its effectiveness in handling coupled differential equations that are extremely nonlinear. The higher‐order differential equations are converted into a first‐order method utilizing the boundary value dilemma (bvp4c) solver, which is part of the MATLAB software package, to computationally analyze the simplified mathematical model. The data obtained demonstrated a high degree of accuracy and symmetry when measured against previously published studies. Following earlier studies, increasing the values of the Prandtl parameters increases the velocity profiles of both basic nanofluid and HNF, while the Forchheimer and porosity parameters reduce fluid velocity. Additionally, as the values of the magnetic parameters increase, the temperature and concentration of simple and HNFs rise as well.

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Large-scale coherent motions in turbulent boundary layers under an adverse pressure gradient up to flow separation

Cited by 8 publications

References 28 publications

Unsteady motions in the turbulent separation bubble of a two-dimensional wing

Unsteady motions in the turbulent separation bubble of a two-dimensional wing

Superstructures in turbulent boundary layers with pressure gradients

Investigating the effect of bio‐convection, chemical reaction, and motile microorganisms on Prandtl hybrid nanofluid flow across a stretching sheet

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