Effects of porous walls on near-wall supersonic turbulence

Chen, Yongkai; Scalo, Carlo

doi:10.1103/physrevfluids.6.084607

Cited by 3 publications

(2 citation statements)

References 32 publications

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“…The gradient of the velocity becomes large near both of the walls because the viscous shear stress is dominant due to the suppression of turbulence. The mean temperature reaches its maximum value around in all cases, as in supersonic and hypersonic channel flows (Chen & Scalo 2021 a , b ), because both of the top and bottom wall temperatures are lower than the recovery temperature, which is proportional to the Mach number squared. The mean temperature variation is strong near the wall, while the variation toward the centre of the channel is mild over .…”

Section: Resultsmentioning

confidence: 97%

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Sub-filter-scale shear stress analysis in hypersonic turbulent Couette flow

Toki,

Sousa,

Chen

et al. 2024

J. Fluid Mech.

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Direct numerical simulations of hypersonic turbulent Couette flows are performed for top-wall Mach numbers of 6, 7 and 8, inspired by non-reactive high-enthalpy wind tunnel free-stream conditions, with the goal of analysing the physical processes driving the sub-filter-scale (SFS) stresses to inform development of large-eddy simulation techniques for hypersonic wall-bounded flows. Semi-local scaling laws collapse mean profiles and second-order turbulent statistics well, in spite of the strong wall-normal gradients of temperature and density. On the other hand, the SFS shear stresses exhibit an unexpected profile characterized by a region of pronounced shear stress deficit, which becomes more pronounced for higher Mach numbers. Instantaneous visualizations suggest that the SFS shear stress deficit is induced by the counter-gradient resolved momentum transport driven by residual velocity motions at the interface between high-density low-speed streaks being ejected away from the wall, and low-density high-speed ones replacing the displaced fluid, qualifying this as a compressibility effect. It is shown that the SFS shear stresses are primarily driven by second-order interactions between residual velocities, in spite of their triply nonlinear nature. This, in turn, motivated a statistical quadrant analysis revealing the presence of a SFS shear stress deficit, that is, SFS processes driving momentum transport of the resolved field towards the top wall. Additionally, higher-Reynolds-number simulations reveal that there is an upper limit of spatial filter widths to resolve large-scale structures, and such deficit is observable at any Reynolds number when a reasonable spatial filter is applied.

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Section: Resultsmentioning

confidence: 97%

“…The code CFDSU has been successfully applied to several wall-bounded hypersonic flows (Sousa et al. 2019; Chen & Scalo 2021 a , b ). The solver adopts a staggered finite-difference scheme.…”

Section: Methodsmentioning

confidence: 99%

Sub-filter-scale shear stress analysis in hypersonic turbulent Couette flow

Toki,

Sousa,

Chen

et al. 2024

J. Fluid Mech.

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Linear stability analysis of second-mode attenuation via porous carbon-matrix ceramics

et al. 2023

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Effects of porous carbon-fiber-reinforced carbon-matrix ceramics (C/C) on the stability of second-mode waves on a 7°-half-angle cone were investigated for Reynolds numbers Rem=2.43×106–6.40×106 m−1 at the freestream Mach number of M∞=7.4, for both sharp and 2.5-mm-round nose tips. A broadband time-domain impedance boundary condition was used to model the effects of the C/C porosity on the flow dynamics leveraging direct ultrasonic benchtop experiments and homogenous absorber theory. A spectral linear stability solver based on orthogonal Laguerre functions, naturally vanishing in the free stream, was used to predict linear spatial growth rates, which are in agreement with independent pulsed axisymmetric direct-numerical simulations. The latter were carried out with the quasi-spectral viscosity closure—a dynamic quasi-spectral procedure capable of deactivating the sub-filter scale stresses in the absence of turbulent break down—verifying its suitability to carry out transitional calculations without affecting ultrasonic wave dynamics. The effectiveness of a porous C/C surface is shown to decrease drastically with static pressure and its presence is shown to decrease the second-mode growth rates in regions where it is unstable as well as increasing the attenuation rates in regions where it is stable.

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A method to extract macroscopic interface data from microscale rough/porous wall flow fields

Kuchibhotla,

Sahoo,

Sudhakar

2023

Physics of Fluids

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Performing geometry-resolved simulations of flows over rough and porous walls is highly expensive due to their multiscale characteristics. Effective models that circumvent this difficulty are often used to investigate the interaction between the free-fluid and such complex walls. These models, by construction, employ an intrinsic averaging process and capture only macroscopic physical processes. However, physical experiments or direct simulations yield micro- and macroscale information, and isolating the macroscopic effect from them is crucial for rigorously validating the accuracy of effective models. Despite the increasing use of effective models, this aspect received the least attention in the literature. This paper presents an efficient averaging technique to extract macroscopic interface data from the flow field obtained via direct simulations or physical experiments. The proposed methodology employs a combination of signal processing and polynomial interpolation techniques to capture the macroscopic information. Results from the ensemble averaging are used as the reference to quantify the accuracy of the proposed method. Compared to the ensemble averaging, the proposed method, while retaining accuracy, is cost-effective for rough and porous walls. To the best of our knowledge, this is the only averaging method that works for poroelastic walls, for which the ensemble averaging fails. Moreover, it applies equally to viscous- and inertia-dominated flows over irregular surfaces.

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Effects of porous walls on near-wall supersonic turbulence

Cited by 3 publications

References 32 publications

Sub-filter-scale shear stress analysis in hypersonic turbulent Couette flow

Sub-filter-scale shear stress analysis in hypersonic turbulent Couette flow

Linear stability analysis of second-mode attenuation via porous carbon-matrix ceramics

A method to extract macroscopic interface data from microscale rough/porous wall flow fields

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