On the role of the laminar/turbulent interface in energy transfer between scales in bypass transition

Yao, Huaijin; Papadakis, George

doi:10.1017/jfm.2023.194

Cited by 3 publications

(1 citation statement)

References 41 publications

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“…Investigations have also studied the energy cascade rates in boundary layer bypass transition (Yao, Mollicone & Papadakis 2022) and flow separation (Mollicone et al 2018). Furthermore, specific attention has been given to the study of inverse cascade in wake flows (Gomes-Fernandes, Ganapathisubramani & Vassilicos 2015;Portela, Papadakis & Vassilicos 2017) and at turbulent/non-turbulent interfaces (Zhou & Vassilicos 2020;Cimarelli et al 2021;Yao & Papadakis 2023).…”

Section: Introductionmentioning

confidence: 99%

Comparing local energy cascade rates in isotropic turbulence using structure-function and filtering formulations

Yao,

Schnaubelt,

Szalay

et al. 2024

J. Fluid Mech.

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Two common definitions of the spatially local rate of kinetic energy cascade at some scale $\ell$ in turbulent flows are (i) the cubic velocity difference term appearing in the ‘scale-integrated local Kolmogorov–Hill’ equation (structure-function approach), and (ii) the subfilter-scale energy flux term in the transport equation for subgrid-scale kinetic energy (filtering approach). We perform a comparative study of both quantities based on direct numerical simulation data of isotropic turbulence at Taylor-scale Reynolds number 1250. While in the past observations of negative subfilter-scale energy flux (backscatter) have led to debates regarding interpretation and relevance of such observations, we argue that the interpretation of the local structure-function-based cascade rate definition is unambiguous since it arises from a divergence term in scale space. Conditional averaging is used to explore the relationship between the local cascade rate and the local filtered viscous dissipation rate as well as filtered velocity gradient tensor properties such as its invariants. We find statistically robust evidence of inverse cascade when both the large-scale rotation rate is strong and the large-scale strain rate is weak. Even stronger net inverse cascading is observed in the ‘vortex compression’ $R>0$ , $Q>0$ quadrant, where $R$ and $Q$ are velocity gradient invariants. Qualitatively similar but quantitatively much weaker trends are observed for the conditionally averaged subfilter-scale energy flux. Flow visualizations show consistent trends, namely that spatially, the inverse cascade events appear to be located within large-scale vortices, specifically in subregions when $R$ is large.

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Section: Introductionmentioning

confidence: 99%

Comparing local energy cascade rates in isotropic turbulence using structure-function and filtering formulations

Yao,

Schnaubelt,

Szalay

et al. 2024

J. Fluid Mech.

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Resolvent analysis of turbulent flow laden with low-inertia particles

Schlander,

Rigopoulos,

Papadakis

2024

J. Fluid Mech.

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We extend the resolvent framework to two-phase flows with low-inertia particles. The particle velocities are modelled using the equilibrium Eulerian model. We analyse the turbulent flow in a vertical pipe with Reynolds number of $5300$ (based on diameter and bulk velocity), for Stokes numbers $St^+=0-1$ , Froude numbers $Fr_z=-4,-0.4,0.4,4$ and $1/Fr_z = 0$ (gravity omitted). The governing equations are written in input–output form and a singular value decomposition is performed on the resolvent operator. As for single-phase flows, the operator is low rank around the critical layer, and the true response can be approximated using one singular vector. Even with a crude forcing model, the formulation can predict physical phenomena observed in Lagrangian simulations, such as particle clustering and gravitational effects. Increasing the Stokes number shifts the predicted concentration spectra to lower wavelengths; this shift also appears in the direct numerical simulation spectra and is due to particle clustering. When gravity is present, there are two critical layers, one for the concentration field, and one for the velocity field. For upward flow, the peak of concentration fluctuations shifts closer to the wall, in agreement with the literature. We explain this with the aid of the different locations of the two critical layers. Finally, the model correctly predicts the interaction of near-wall vortices with particle clusters. Overall, the resolvent operator provides a useful framework to explain and interpret many features observed in Lagrangian simulations. The application of the resolvent framework to higher $St^+$ flows in combination with Lagrangian simulations is also discussed.

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Role of flow structures on the deposition of low-inertia particles in turbulent pipe flow

Schlander,

Rigopoulos,

Papadakis

2024

Phys. Rev. Fluids

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We analyze the effect of large-scale coherent structures on the deposition of low-inertia particles in a turbulent pipe flow using extended proper orthogonal decomposition (EPOD) and spectral analysis. We perform direct numerical simulations (DNSs) at two the Reynolds numbers 5300 and 10 300 (based on bulk parameters) with the particles released at the pipe inlet. The equilibrium Eulerian model is employed for calculating particle velocity, and the analysis is limited to particles with Stokes number (based on wall units) less than 1. Increasing the Stokes number increases the energy at small streamwise wavelengths (due to inertial clustering), and the spectral energy peak moves from λz+≈1000 to λz+≈150. The spectral peak in the (λz+,y+) plane, where y+ is the wall-normal distance, moves from the buffer layer to the logarithmic region. Gravity has a substantial effect on the POD mode shapes. For the downward flow, a second peak appears closer to the center. A new Fukagata-Iwamoto-Kasagi (FIK) identity is derived for the wall deposition rate coefficient (Sherwood number, Sh) and employed to quantify the contributions of the mean and fluctuating velocity and particle concentration fields for different Stokes, Froude, and Reynolds numbers. Modes with azimuthal wave numbers kθ equal to three or four are found to contribute most to deposition. Application of the developed methodology to higher Reynolds number can elucidate the role of large- and very-large-scale flow structures on particle deposition to the wall. It is well known these structures leave their footprint at the wall but their contribution to deposition is not well understood. Published by the American Physical Society 2024

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On the role of the laminar/turbulent interface in energy transfer between scales in bypass transition

Cited by 3 publications

References 41 publications

Comparing local energy cascade rates in isotropic turbulence using structure-function and filtering formulations

Comparing local energy cascade rates in isotropic turbulence using structure-function and filtering formulations

Resolvent analysis of turbulent flow laden with low-inertia particles

Role of flow structures on the deposition of low-inertia particles in turbulent pipe flow

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