Energy transfer mechanisms in adverse pressure gradient turbulent boundary layers: production and inter-component redistribution

Gungor, Taygun R.; Maciel, Yvan; Gungor, Ayse G.

doi:10.1017/jfm.2022.679

Cited by 8 publications

(21 citation statements)

References 61 publications

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“…Most of the energy is observed to be contained in wavelengths , as expected (Gungor et al. 2022). Under an increasing cumulative upstream FPG (figure 11 b – f ), the stabilising effect of the acceleration causes the wall-normal structures to significantly lose energy throughout the boundary layer.…”

Section: Resultssupporting

confidence: 83%

“…The production of TKE and uv-RS remaining ‘turned off’ within the APG region could partially explain the reduction in outer peak magnitudes of the Reynolds stresses observed with in figure 4( b – d ) for the stronger pressure gradients, in contrast to the increase expected of a typical APG TBL (Gungor et al. 2022). Lastly, the production profiles that result at station for the six FAPG cases are shown in figure 9( b , d ).…”

Section: Resultsmentioning

confidence: 84%

“…Since large scales are considered essential for the production and inter-component transfer of turbulence in the outer region (Bradshaw 1967; Gungor et al. 2022), the reduction of strength and/or population of large scales inferred from the PSDs at station could explain the production of TKE and uv-RS in the outer region diminishing as the FAPG strength is statically increased (figure 9). The shift in energy towards longer wavelengths near the wall for increasing upstream FPG strength seen here is consistent with work by Warnack & Fernholz (1998) and Dixit & Ramesh (2008), among others, who have reported ‘stretched’ and ‘flattened’ long structures under FPGs.…”

Section: Resultsmentioning

confidence: 99%

“…The mean velocity develops a thinner viscous sublayer and a thicker wake region. The departure from universal logarithmic behaviour depends on , with significant departures seen for (Gungor, Maciel & Gungor 2022). An increase in production in the outer region causes a strengthening outer peak in the Reynolds stresses, regardless of the choice of local inner or outer scaling, even for mild APGs.…”

Section: Introductionmentioning

confidence: 97%

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A family of adverse pressure gradient turbulent boundary layers with upstream favourable pressure gradients

Parthasarathy

Saxton-Fox

2023

J. Fluid Mech.

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A flat-plate turbulent boundary layer (TBL) is experimentally subjected to a family of 22 favourable–adverse pressure gradients (FAPGs) using a ceiling panel of variable convex curvature. We define FAPGs as a sequence of streamwise pressure gradients in the order of favourable followed by adverse, similar in sequence to the pressure gradients over the suction side of an airfoil. For the strongest pressure gradient case, the acceleration parameter, $K$ , varied spatially from $6 \times 10^{-6}$ to $- 4.8 \times 10^{-6}$ . The adverse pressure gradient (APG) region of this configuration is studied using particle image velocimetry in the streamwise–wall-normal plane. The statistics of the APG TBL show that the upstream favourable pressure gradient (FPG) exerts a strong and lasting downstream influence, and that the rapid spatial changes in the pressure gradients imposed cause an internal boundary layer to grow within the TBL for 15 of the cases studied. The internal layer typically occupies 20 $\%$ of the boundary layer thickness and dominates the boundary layer response, containing the peak turbulent production, peak strength and population of vortices, and most of the spectral energy content of the flow. The outer layer, on the other hand, develops in the APG region without considerable changes to the state dictated by the upstream FPG. These trends are in contrast to APG TBLs that originate from a zero pressure gradient region, where the outer/wake region is known to dominate TBL response. The observed changes are quantified across the family of FAPGs imposed.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 84%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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A family of adverse pressure gradient turbulent boundary layers with upstream favourable pressure gradients

Parthasarathy

Saxton-Fox

2023

J. Fluid Mech.

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“…2017; Gungor et al. 2022). More recently, Wei & Knopp (2023) employed a similar scaling form but made changes to the velocity and length scales throughout the scaling process.…”

Section: Introductionmentioning

confidence: 99%

Consistent outer scaling and analysis of adverse pressure gradient turbulent boundary layers

Han,

Ma,

Yan

2024

J. Fluid Mech.

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Under adverse pressure gradient (APG) conditions, the outer regions of turbulent boundary layers (TBLs) are characterized by an increased velocity defect $U_{e}-U$ , an outwards shift of the peak value of the Reynolds shear stress $-\langle uv\rangle$ and an appearance of the outer peak value of the Reynolds normal stress $\langle uu\rangle$ . Here $U_{e}$ is the TBL edge velocity. Scaling APG TBLs is challenging due to the non-equilibrium effects caused by changes in the APG. To address this, the response distance of TBLs to non-equilibrium conditions is utilized to extend the Zagarola–Smits scaling $U_{zs} = U_{e}({\delta ^{*} }/{\delta })$ and ensure that the original properties of the Zagarola–Smits scaling are maintained as $Re \to \infty$ . Here $\delta ^{*}$ is the displacement thickness and $\delta$ is the boundary layer thickness. Based on the established correlation between $U_{e}-U$ and $-\langle uv\rangle$ , the scaling is extended to $-\langle uv\rangle$ . Furthermore, considering the coupling relationship between Reynolds stress components, the scaling is extended to encompass each Reynolds stress component. The proposed consistent scaling is verified using five non-equilibrium databases and five near-equilibrium databases, successfully collapsing the data of the TBL outer region. The pressure gradient parameter $\beta =({\delta ^{*} }/{\rho u_{\tau }^{2} }) ({\mathrm {d} P_{e} }/{\mathrm {d}\kern0.7pt x})$ of these databases spans two orders of magnitude. Here $P_{e}$ is the boundary layer edge pressure, $u_{\tau }$ is the friction velocity and $\rho$ is the density. Finally, the influence of the APG on the inner and outer regions of TBLs is analysed using the mean momentum balance equation. The analysis suggests that the shift of the $-\langle uv\rangle$ peak to the outer region under APG conditions is due to an insufficient inertia term near the inner region to balance the APG. It is observed that the APG promotes interaction between the inner and outer regions of TBLs, but the inner and outer regions still retain distinctive properties.

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Energy Transfer in Turbulent Boundary Layers with Adverse Pressure Gradient

Gungor

Maciel

2021

Springer Proceedings in Physics

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Two direct numerical simulation (DNS) databases are investigated to understand the effect of the outer-layer turbulence on the inner layer's structures and energy transfer mechanisms. The first DNS database is the non-equilibrium adverse-pressure-gradient (APG) turbulence boundary layer (TBL) of Gungor et al. [1]. Its Reynolds number and the inner-layer pressure gradient parameter reach above 8000 and 10, respectively. The shape factor spans between 1.4 and 3.3, which indicates the flow has various velocity defect situations. The second database is the same flow as the first one but the outer layer turbulence is artificially eliminated in this flow. Turbulence is removed above 0.15 local boundary layer thickness. For the analysis, we chose four streamwise positions with small, moderate, large, and very-large velocity defect. We compare the wall-normal distribution of Reynolds stresses, two-point correlations and spectral distributions of energy, production and pressure strain. The results show that the inner layer turbulence can sustain itself when the outer-layer turbulence does not exist regardless of the velocity defect or the pressure gradient. The two-point correlations of both cases show that outer large-scale structures affect the inner layer structures significantly. The streamwise extent of the correlation contours scales with pressure-viscous units. This shows the importance of the pressure gradient's effect on the inner-layer structures. The spectral distributions demonstrate that the energy transfer mechanisms are probably the same in the inner layer regardless of the velocity defect, which suggests the near-wall cycle may exist even in very-large defect APG TBLs where the mean shear in the inner layer is considerably lower than small-defect APG TBLs.

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Energy transfer mechanisms in adverse pressure gradient turbulent boundary layers: production and inter-component redistribution

Cited by 8 publications

References 61 publications

A family of adverse pressure gradient turbulent boundary layers with upstream favourable pressure gradients

A family of adverse pressure gradient turbulent boundary layers with upstream favourable pressure gradients

Consistent outer scaling and analysis of adverse pressure gradient turbulent boundary layers

Energy Transfer in Turbulent Boundary Layers with Adverse Pressure Gradient

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