The sixth seminar of the UniCFD Laboratory of ISP RAS will host on November 13th, 2018 in the Institute for System Programming of the RAS, room 110 at 15:00.
The theme of the seminar:
Computational investigation of instability and turbulence development in problems of multiphase and stratified medium.
d.p.-m.s. Yakovenko Sergei Nikolayevich (ITAM SB RAS, Novosibirsk)
Results of incompressible flows simulation for two evolution problems are presented:
- unmixable medium interfaces (fluid-fluid, gas-fluid);
- internal waves, created by an obstacle in a flow with stable stratification.
In order to verify calculation methods (1) classical test flows are examined under: (a) breaking of a dam and spreading of water over horizontal dry floor ; (b) development of Rayleigh-Taylor instability (RTI) [2,3]. Problem (1а) represents hydrophysics issues: propagation of wave, surge, tsunami over horizontal and inclined floor, flooding of territories due to planned or emergency water discharge from a storage reservoir. Problem (1b) corresponds to many events from micro- to astrophysics scale and is important for processes of internal waves breaking during their evolution in (1a).
The classical test for (2) is a flow with constant velocity and input density gradient values and bidimensional obstacle located across the flow [4–6], which corresponds to experiments with hauled body in hydrodynamic channel. Such flows take place in nature which calls for their adequate description. For instance, under lee waves breaking an orographic turbulence occurs which is dangerous for aviation. Internal waves breaking processes play an important role in atmospheric and oceanic circulation, leading to large-scale transfer of momentum, energy and different inclusions.
Calculations of RTI development on medium interface using continuum model (CSF) of surface tension shows effect of viscous and surface tension damping in accordance with theory and experience at linear stability stage and non-linear phase with perturbations growth velocity saturation. Under huge density drop heavy medium’s thin trickles interpenetrate thick columns of light-dense medium. Under small density drop at non-linear phase the Kelvin-Helmholtz instability occurs with distinctive mushroom-shaped convective structures.
Under internal waves breaking in a flow with stable stratification with an obstacle unstable layers with steep density gradients and similar structures are being formed as well. Structures’ interaction leads to formation of vigorous mixing zones with small density gradients and production balance, advection and turbulence power dissipation. Thus, it is showed that geophysical turbulence emergence under wave breaking can occur due to Rayleigh-Taylor instability, and scenarios of turbulence transition under different conditions are examined.
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