Velocity and Temperature Profiles in Turbulent Channel Flow at Supercritical Pressure

Toki, Takahiko; Teramoto, Shinji; Okamoto, Koji

doi:10.2514/1.b37381

Cited by 18 publications

(23 citation statements)

References 28 publications

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“…However, the same similarity is not observed for the turbulent heat fluxes, including in the near-wall thermal boundary layer (regions with large gradients in mean temperature, as can be observed in profiles of the mean temperature provided in figure 25a). The significant dissimilarity in turbulent heat flux profiles seen here was not observed in cases with lower temperature ratio values (Toki et al 2020).…”

Section: Instantaneous Contours and Fluctuation Profilescontrasting

confidence: 46%

“…For N 2 at temperatures and pressures comparable to those used in our current investigation, Chung's model demonstrates average absolute deviations below 1.24% for μ and 7.30% for λ when compared to experimental data; both values lie within typical experimental uncertainty ranges. With its relative accuracy and computational efficiency, this model has also been used by a number of previous studies of transcritical turbulence (Ruiz 2012;Toki et al 2020).…”

Section: Governing Equations Thermodynamic Models and Domain Definitionmentioning

confidence: 99%

“…A second transformation proposed by Toki et al (2020) is derived using the mixing length hypothesis for both momentum and energy and also by assuming linear shear stress and heat flux. This transformation is written as…”

Section: Assessment Of Previous Mean Temperature Theoretical Workmentioning

confidence: 99%

“…Recent computational investigations have utilized more realistic thermodynamic models in an effort to examine conditions that are more representative of real-world transcritical turbulence. Toki, Teramoto & Okamoto (2020) presented results for turbulent transcritical channel flow calculations at density ratios Ω = 4 and Ω = 8 before proposing a mixing-length model to transform the mean temperature profile. Comparisons of results from their transformation with incompressible DNS data by Morinishi, Tamano & Nakamura (2007) appeared successful, conditional on allowing the amount of shift in the logarithmic region to be fitted empirically a posteriori.…”

Section: Introductionmentioning

confidence: 99%

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Structure of the thermal boundary layer in turbulent channel flows at transcritical conditions

2022

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Enhanced fluctuations, steep gradients, and intensified heat transfer are characteristics of wall-bounded turbulence at transcritical conditions. Although such conditions are prevalent in numerous technical applications, the structure of the thermal boundary layer under realistic density gradients and heating conditions remains poorly understood. Specifically, statistical descriptions of the temperature field in such flows are provided inconsistently using existing models. To address this issue, direct numerical simulations are performed by considering fully developed transcritical turbulent channel flow at pressure and temperature conditions that cause density changes of a factor of up to $O(20)$ between the hot and cold walls. As a consequence of the proximity of the Widom line to the hot wall, significant asymmetries are observed when comparing regions near the cold wall and near the hot wall. Previous transformations that attempt to collapse the near-wall mean temperature profiles among different cases to a single curve are examined. By addressing model deficiencies of these transformations, a formulation for an improved mean temperature transformation is proposed, with appropriate considerations for real fluid effects that involve strong variations in thermodynamic quantities. Our proposed transformation is shown to perform well in collapsing the slope of the logarithmic region to a single universal value with reduced uncertainty. Coupled with a predictive framework to estimate the non-universal shift parameter of the logarithmic region using a priori information, our transformation provides an analytic profile to model the near-wall mean temperature. These results thus provide a framework to guide the development of models for wall-bounded transcritical turbulence.

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Section: Instantaneous Contours and Fluctuation Profilescontrasting

confidence: 46%

Section: Governing Equations Thermodynamic Models and Domain Definitionmentioning

confidence: 99%

Section: Assessment Of Previous Mean Temperature Theoretical Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure of the thermal boundary layer in turbulent channel flows at transcritical conditions

2022

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“…Ma, Yang & Ihme (2018) used fully compressible DNS to study a planar turbulent channel flow of supercritical nitrogen and demonstrated that semilocal scaling has limited success near a wall where violent fluctuations are found. Toki, Teramoto & Okamoto (2020) also simulated a planar turbulent channel flow of supercritical nitrogen and introduced a new transformation equation for the temperature profile in the logarithmic region. Transcritical channel flow of R-134a was simulated by Kim, Hickey & Scalo (2019) and it was reported that even the recent improvements to the scaling laws cannot accurately capture the velocity distribution in that transcritical flow.…”

Section: Introductionmentioning

confidence: 99%

Investigation of species-mass diffusion in binary-species boundary layers at high pressure using direct numerical simulations

Toki

Bellan

2021

J. Fluid Mech.

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Direct numerical simulations of single-species and binary-species temporal boundary layers at high pressure are performed with special attention to species-mass diffusion. The working fluids are nitrogen or a mixture of nitrogen and methane. Mean profiles and turbulent fluctuations of mass fraction show that their qualitative characteristics are different from those of streamwise velocity and temperature, due to the different boundary conditions. In a wall-parallel plane near the wall, the streamwise velocity and temperature have streaky patterns and the fields are similar. However, the mass fraction field at the same location is different from the streamwise velocity and temperature fields indicating that species-mass diffusion is not similar to the momentum and thermal diffusion. In contrast, at the centre and near the edge of the boundary layer, the mass fraction and temperature fields have almost the same pattern, indicating that the similarity between thermal and species-mass diffusion holds away from the wall. The lack of similarity near the wall is traced to the Soret effect that induces a temperature-gradient-dependent species-mass flux. As a result, a new phenomenon has been identified for a non-isothermal binary-species system – uphill diffusion, which in its classical isothermal definition can only occur for three or more species. A quadrant analysis for the turbulent mass flux reveals that near the wall the Soret effect enhances the negative contributions of the quadrants. Due to the enhancement of the negative contributions, small species-concentration fluid tends to be trapped near the wall.

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Velocity transformation for compressible wall-bounded turbulence—An approach through the mixing length hypothesis

Zhu,

Song,

Yang

et al. 2024

Sci. China Phys. Mech. Astron.

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Velocity and Temperature Profiles in Turbulent Channel Flow at Supercritical Pressure

Cited by 18 publications

References 28 publications

Structure of the thermal boundary layer in turbulent channel flows at transcritical conditions

Structure of the thermal boundary layer in turbulent channel flows at transcritical conditions

Investigation of species-mass diffusion in binary-species boundary layers at high pressure using direct numerical simulations

Velocity transformation for compressible wall-bounded turbulence—An approach through the mixing length hypothesis

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