Vibrational relaxation in compressible isotropic turbulence with thermal nonequilibrium

Zheng, Qinmin; Wang, Jianchun; Noack, Bernd R.; Li, Hui; Wan, Minping; Chen, Shiyi

doi:10.1103/physrevfluids.5.044602

Cited by 8 publications

(18 citation statements)

References 32 publications

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“…The temperature-dependent viscosity (μ) and thermal conductivity coefficients (κ tr and κ v ) are specified by Sutherland's and Eucken's laws. For their detailed expressions, please refer to our previous publication (Zheng et al 2020).…”

Section: Governing Equations and Numerical Methodsmentioning

confidence: 99%

“…where C and K 2 are the dimensionless constants relating to the molecular structure of gases. Following the previous literature (Donzis & Maqui 2016;Khurshid & Donzis 2019;Zheng et al 2020), the dimensionless parameter K τ = τ v /τ η is adopted to characterize the time scale of the relaxation process. The • operator stands for spatial average.…”

Section: Governing Equations and Numerical Methodsmentioning

confidence: 99%

“…Nevertheless, the impact of turbulent fluctuation was ignored in most of the prior literature about vibrational non-equilibrium. Only a small percentage of investigations discussed the interaction between turbulent fluctuation and vibrational relaxation, as pioneered by Donzis & Maqui (2016), Khurshid & Donzis (2019) and Zheng et al (2020) in compressible isotropic turbulence. As effects of the initial and boundary conditions are excluded, the compressible isotropic turbulence is an excellent flow model for studying the quantitative statistical properties of turbulence.…”

Section: Introductionmentioning

confidence: 99%

“…The dissipation thus increases temporarily and further results in a faster turbulence decay. Zheng et al (2020) discussed the effects of compressibility and vibrational relaxation on the statistical properties of vibrational rate and dissipation/production of vibrational energy fluctuation, in the stationary compressible isotropic turbulence with vibrational non-equilibrium. When the relaxation time is small enough, on average, the internal energy transfers from the translational-rotational to vibrational modes in the compression region and in the inverse direction in the expansion region.…”

Section: Introductionmentioning

confidence: 99%

“…However, there is no direct exchange path between the vibrational and kinetic energies. In present simulations, different from the previous works (Donzis & Maqui 2016;Khurshid & Donzis 2019;Zheng et al 2020), both large-scale momentum forcing and thermal forcing are adopted, to maintain the turbulence in a statistically stationary state and to inject the large-scale temperature fluctuation. We will mainly focus on the combined impact of vibrational relaxation and large-scale thermal forcing on the statistical properties of turbulence and the transfer of internal energy fluctuation.…”

Section: Introductionmentioning

confidence: 99%

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Transfer of internal energy fluctuation in compressible isotropic turbulence with vibrational non-equilibrium

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Section: Governing Equations and Numerical Methodsmentioning

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Section: Governing Equations and Numerical Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transfer of internal energy fluctuation in compressible isotropic turbulence with vibrational non-equilibrium

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Effect of wall temperature on the kinetic energy transfer in a hypersonic turbulent boundary layer

Xu¹,

Wang²,

Wan³

et al. 2021

J. Fluid Mech.

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The effect of wall temperature on the transfer of kinetic energy in a hypersonic turbulent boundary layer for different Mach numbers and wall temperature ratios is studied by direct numerical simulation. A cold wall temperature can enhance the compressibility effect in the near-wall region through increasing the temperature gradient and wall heat flux. It is shown that the cold wall temperature enhances the local reverse transfer of kinetic energy from small scales to large scales, and suppresses the local direct transfer of kinetic energy from large scales to small scales. The average filtered spatial convection and average filtered viscous dissipation are dominant in the near-wall region, while the average subgrid-scale flux of kinetic energy achieves its peak value in the buffer layer. It is found that the wall can suppress the inter-scale transfer of kinetic energy, especially for the situation of a cold wall. A strong local reverse transfer of fluctuating kinetic energy is identified in the buffer layer in the inertial range. Helmholtz decomposition is applied to analyse the compressibility effect on the subgrid-scale flux of kinetic energy. A strong transfer of the solenoidal component of fluctuating kinetic energy is identified in the buffer layer, while a significant transfer of the dilatational component of fluctuating kinetic energy is observed in the near-wall region. It is also shown that compression motions have a major contribution to the direct transfer of fluctuating kinetic energy, while expansion motions play a marked role in the reverse transfer of fluctuating kinetic energy.

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Thermochemical non-equilibrium effects in turbulent hypersonic boundary layers

et al. 2022

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A hypersonic, spatially evolving turbulent boundary layer at Mach 12.48 with a cooled wall is analysed by means of direct numerical simulations. At the selected conditions, massive kinetic-to-internal energy conversion triggers thermal and chemical non-equilibrium phenomena. Air is assumed to behave as a five-species reacting mixture, and a two-temperature model is adopted to account for vibrational non-equilibrium. Wall cooling partly counteracts the effects of friction heating, and the temperature rise in the boundary layer excites vibrational energy modes while inducing mild chemical dissociation of oxygen. Vibrational non-equilibrium is mostly driven by molecular nitrogen, characterized by slower relaxation rates than the other molecules in the mixture. The results reveal that thermal non-equilibrium is sustained by turbulent mixing: sweep and ejection events efficiently redistribute the gas, contributing to the generation of a vibrationally under-excited state close to the wall, and an over-excited state in the outer region of the boundary layer. The tight coupling between turbulence and thermal effects is quantified by defining an interaction indicator. A modelling strategy for the vibrational energy turbulent flux is proposed, based on the definition of a vibrational turbulent Prandtl number. The validity of the strong Reynolds analogy under thermal non-equilibrium is also evaluated. Strong compressibility effects promote the translational–vibrational energy exchange, but no preferential correlation was detected between expansions/compressions and vibrational over-/under-excitation, as opposed to what has been observed for unconfined turbulent configurations.

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Vibrational relaxation in compressible isotropic turbulence with thermal nonequilibrium

Cited by 8 publications

References 32 publications

Transfer of internal energy fluctuation in compressible isotropic turbulence with vibrational non-equilibrium

Transfer of internal energy fluctuation in compressible isotropic turbulence with vibrational non-equilibrium

Effect of wall temperature on the kinetic energy transfer in a hypersonic turbulent boundary layer

Thermochemical non-equilibrium effects in turbulent hypersonic boundary layers

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