EGU21-10311
https://doi.org/10.5194/egusphere-egu21-10311
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Optimal energy growth in stably stratified turbulent Couette flow

Grigory Zasko1,2, Andrey Glazunov1, Evgeny Mortikov3, Yuri Nechepurenko1,2, and Pavel Perezhogin1
Grigory Zasko et al.
  • 1Marchuk Institute of Numerical Mathematics of the Russian Academy of Sciences, Moscow, Russian Federation (zasko.gr@bk.ru)
  • 2Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences, Moscow, Russian Federation
  • 3Lomonosov Moscow State University, Research Computing Center, Moscow, Russian Federation

In this report, we will try to explain the emergence of large-scale organized structures in stably stratified turbulent flows using optimal disturbances of the mean turbulent flow. These structures have been recently obtained in numerical simulations of turbulent stably stratified flows [1] (Ekman layer, LES) and [2] (plane Couette flow, DNS and LES) and indirectly confirmed by field measurements in the stable boundary layer of the atmosphere [1, 2]. In instantaneous temperature fields they manifest themselves as irregular inclined thin layers with large gradients (fronts), spaced from each other by distances comparable to the height of the entire turbulent layer, and separated by regions with weak stratification.

Optimal disturbances of a stably stratified turbulent plane Couette flow are investigated in a wide range of Reynolds and Richardson numbers. These disturbances were computed based on a simplified linearized system of equations in which turbulent Reynolds stresses and heat fluxes were approximated by isotropic viscosity and diffusion with coefficients obtained from DNS results. It was shown [3] that the spatial scales and configurations of the inclined structures extracted from DNS data coincide with the ones obtained from optimal disturbances of the mean turbulent flow.

Critical value of the stability parameter is found starting from which the optimal disturbances resemble inclined structures. The physical mechanisms that determine the evolution, energetics and spatial configuration of these optimal disturbances are discussed. The effects due to the presence of stable stratification are highlighted.

Numerical experiments with optimal disturbances were supported by the RSF (grant No. 17-71-20149). Direct numerical simulation of stratified turbulent Couette flow was supported by the RFBR (grant No. 20-05-00776).

References:

[1] P.P. Sullivan, J.C. Weil, E.G. Patton, H.J. Jonker, D.V. Mironov. Turbulent winds and temperature fronts in large-eddy simulations of the stable atmospheric boundary layer // J. Atmos. Sci., 2016, V. 73, P. 1815-1840.

[2] A.V. Glazunov, E.V. Mortikov, K.V. Barskov, E.V. Kadantsev, S.S. Zilitinkevich. Layered structure of stably stratified turbulent shear flows // Izv. Atmos. Ocean. Phys., 2019, V. 55, P. 312–323.

[3] G.V. Zasko, A.V. Glazunov, E.V. Mortikov, Yu.M. Nechepurenko. Large-scale structures in stratified turbulent Couette flow and optimal disturbances // Russ. J. Num. Anal. Math. Model., 2010, V. 35, P. 35–53.

How to cite: Zasko, G., Glazunov, A., Mortikov, E., Nechepurenko, Y., and Perezhogin, P.: Optimal energy growth in stably stratified turbulent Couette flow, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10311, https://doi.org/10.5194/egusphere-egu21-10311, 2021.

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