Exact coherent solutions for the filtered large scale motions in turbulent Couette flow - Archive ouverte HAL
Communication Dans Un Congrès Année : 2015

Exact coherent solutions for the filtered large scale motions in turbulent Couette flow

Résumé

We investigate the nature of large-scale motions (LSM) in turbulent Couette flow. It is first shown that large-scale motions are self-sustained by verifying that they survive even when active processes at smaller scales are artificially quenched (see figure 1) in over-damped large eddy simulations as in [1, 2]. We then investigate the nature of the self-sustained large-scale motions by looking for exact solutions of the filtered, possibly over-damped, (LES) equations. The edge state of coherent large-scale motions is computed by edge-tracking and is found to be a non-trivial exact steady solution of the filtered equations. Newton-Krylov iterations are used to prove convergence of the steady solution and to perform parameter-continuations. By continuation to higher values of the over-damping it is shown that the lower branch edge state is connected to an upper branch solution via a saddle-node bifurcation. We have been able to compute upper branch solutions of the filtered equations at Reynolds numbers up to Re = 2150 using specific paths in the Reynolds number-overdamping parameter plane (see figure 2). These solutions are then continued to Navier-Stokes solutions by reducing to zero the residual stress in the LES. It is finally shown that the steady large-scale solutions of the filtered equations motions can be connected by continuation to the Nagata-Clever-Busse-Waleffe solutions of the Navier-Stokes equations. Financial support from PRES Université de Toulouse and Région Midi-Pyrénées is kindly acknowledged. References [1] Y. Hwang and C. Cossu. Self-sustained process at large scales in turbulent channel flow. Phys. Rev. Lett., 105(4):044505, 2010. [2] Y. Hwang and C. Cossu. Self-sustained processes in the logarithmic layer of turbulent channel flows. Phys. Fluids,
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hal-02869100 , version 1 (19-06-2020)

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  • HAL Id : hal-02869100 , version 1

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Subhandu Rawat, Carlo Cossu, Yongyun Hwang, Francois Rincon. Exact coherent solutions for the filtered large scale motions in turbulent Couette flow. EuroMech Colloquium 568 Coherent structures in fully developed turbulence, School of Aeronautics, Univerdidad Politècnica Madrid, May 2015, Madrid, Spain. ⟨hal-02869100⟩
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