The walls move at constant speed in opposite directions along x: the top towards the back of the cell, the bottom towards the front, with no-slip boundary conditions. The top wall and the upper half of the fluid are cut away to show what happens inside.

Color indicates u(x,t), the steamwise speed of the fluid:

red indicates fluid being dragged away from the viewer by the top wall; blue, towards.

Arrows:

fluid velocity in the section plane.

Three 2D instantanenous fluid sections are shown:

• the midplane velocity field [u,w](x,0,z,t), halfway between the upper and lower walls
• a spanwise/wall-normal velocity field [v,w](0,y,z,t), front section and back top section
• a streamwise/wall-normal velocity field [u,v](x,y,0,t), bottom right and top left section