Windtunnel for MC_Escher_WindMill

I am working on a 3D print windmill and wind tunnel. These models are the results of my testing done in the period of June 2014 till October 2015.

The wind tunnel is inspired by examples of existing versions. The wind tunnel helps to increase airspeed thanks to it's shape (that causes differences in air pressure) (Venturi effect) What I tried is to create internal air-tubes for extra air to get inside. The round shape is a perfect housing for a spherical mill.

Note; Scale the MC Escher mill to a size that fits inside the tunnel. Mind a spare of 5% because the mill grows bigger when turning (and could touch the walls inside)