This snapshot shows an instant in the evolution of plane Couette flow in a rectangular cell of size
[Lx, Ly, Lz] with solid walls on the top and bottom (y = -Ly/2 and Ly/2).
The [x,y,z] directions are refered to as streamwise, wall-normal and spanwise, respectively,
with the three velocity components denoted by
u(x,t) = [u,v,w](x,y,z,t) .