Molecular-gas-dynamics simulations of turbulent Couette flow over a mean-free-path-scale permeable substrate

Journal Article · Mon Aug 28 00:00:00 EDT 2023 · Physical Review Fluids (Online)

DOI:https://doi.org/10.1103/physrevfluids.8.083401· OSTI ID:2311668

McMullen, Ryan Michael  ^[1]; Krygier, Michael C.  ^[2]; Torczynski, John R.  ^[1]; Gallis, Michael A.  ^[1]

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1. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States). Engineering Sciences Center
2. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States). Center for Computing Research

Here we report flow statistics and visualizations from molecular-gas-dynamics simulations using the direct simulation Monte Carlo (DSMC) method for turbulent Couette flow in a minimal domain where the lower wall is replaced by an idealized permeable fibrous substrate representative of thermal-protection-system materials for which the Knudsen number is O(10^-1). Comparisons are made with smooth-wall DSMC simulations and smooth-wall direct numerical simulations (DNS) of the Navier-Stokes equations for the same conditions. Roughness, permeability, and noncontinuum effects are assessed. In the range of Reynolds numbers considered herein, the scalings of the skin friction on the permeable substrate and of the mean flow within the substrate suggest that they are dominated by viscous effects. While the regenerative cycle characteristic of smooth-wall turbulence remains intact for all cases considered, we observe that the near-wall velocity fluctuations are modulated by the permeable substrate with a wavelength equal to the pore spacing. Additionally, the flow within the substrate shows significant rarefaction effects, resulting in an apparent permeability that is 13% larger than the intrinsic permeability. In contrast, the smooth-wall DSMC and DNS simulations exhibit remarkably good agreement for the statistics examined, despite the Knudsen number based on the viscous length scale being as large as O(10^-1). This latter result is at variance with classical estimates for the breakdown of the continuum assumption and calls for further investigations into the interaction of noncontinuum effects and turbulence.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0003525
• OSTI ID: 2311668
• Report Number(s): SAND-2023-08640J
• Journal Information: Physical Review Fluids (Online), Vol. 8, Issue 8; ISSN 2469-990X
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
molecular dynamics
noncontinuum effects
porous media
turbulence