СЕМИНАР ПО МЕХАНИКЕ СПЛОШНЫХ СРЕД

Уважаемые коллеги!

В среду, 24 мая 2017 г., в кинозале Института механики МГУ в 12.00 состоится очередное заседание семинара по механике сплошных сред под руководством А.Г. Куликовского, В.П. Карликова и О.Э. Мельника.

Alexander Yakhot

Department of Mechanical Engineering, Ben-Gurion University, Beersheva, Israel

TURBULENCE IN A LOCALIZED PUFF IN A PIPE

We have performed direct numerical simulations of transient turbulence in pipe flow for Re=2,250 which is established as a threshold of a localized puff. The results confirm the existence of a spatio-temporal intermittency, when turbulence is localized in a puff travelling downstream. To assimilate the velocity data, we apply a conditional sampling based on the location of the maximum energy of the transverse (turbulent) motion. Specifically, at each time instance, we follow a turbulent puff by a three-dimensional moving-window centered at that location. We collected a snapshot-ensemble of the velocity fields acquired over 10,000 time instances (snapshots) inside the moving-window. The considered flow is intermittent, transitional. The velocity field inside the puff shows the dynamics of a developing turbulence. The localized puff is about of 12-15 pipe diameters long with almost laminar trailing and leading edges. In the puff core, along the moving-window, it takes the downstream short distance of several pipe diameters to form the state of developed turbulence, when the turbulence statistics becomes similar to fully-developed turbulent pipe flow; the velocity profile becomes flat in the pipe core and logarithmic in the vicinity of the wall. It is shown that this “fully-developed turbulent slot” is very narrow, about 2 pipe diameters; it is localized and moves with a puff.