Coherent structures in Dissipative Particle Dynamics simulations of the transition to turbu.pdf

Coherent structures in Dissipative Particle Dynamics simulations of the transition to turbulence in compressible shear flows Jan-Willem van de Meent, Alexander Morozov,∗ Ell´ak Somfai,† Eric Sultan, and Wim van Saarloos Instituut-Lorentz, University of Leiden, Postbus 9506, 2300 RA Leiden, The Netherlands We present simulations of coherent structures in compressible flows near the transition to turbu- lence using the Dissipative Particle Dynamics (DPD) method. The structures we find are remarkably consistent with experimental observations and DNS simulations of incompressible flows, despite a difference in Mach number of several orders of magnitude. The bifurcation from the laminar flow is bistable and shifts to higher Reynolds numbers when the fluid becomes more compressible. This 8 work underlines the robustness of coherent structures in the transition to turbulence and illustrates 0 the ability of particle-based methods to reproduce complex non-linear instabilities. 0 2 PACS numbers: 47.27.E-,47.11.-j,47.27.Cn l u J The transition to turbulence in parallel shear flows like 7 pressure-driven channel flow or flow in a pipe is one of the classic problems of fluid mechanics. Until recently even ] predicting the correct order of magnitude for the transi- n y tional Reynolds number Re was problematic. This situ- d ation has changed with the discovery of exact nonlinear - solutions of the Navier-Stokes equations [1–6]. These so- u l lutions are dominated by streaks and streamwise vortices f. – low-dimensional coherent s