  We present results of the study of a turbulent air flow with a large scale
circulation in Rayleigh-Benard rectangular convective cell with a heated bottom
wall and a cooled top wall. The mean horizontal velocity of the main roll and
the mean vorticity of eddy rings are almost aligned in a large part of the
flow. The helicity of the mean flow is quite high, and is the source of
turbulent helicity. Since helicity of the mean flow and turbulence is quite
large, the flow in Rayleigh-Benard convective cell is well suited to study
properties of helical turbulence.
