In an experiment in hydraulics lab of my college, very recently someone asked me, why were there two fans in the open circuit wind tunnel.
That wind tunnel is used for conducting experiment for finding boundary layer thickness over a flat plate.
Momentum thickness, displacement thickness and energy thickness, over a flat plate.
probably because one fan would not develop enough pressure rise to drive the tunnel to its specified operating condition. This would be true if the fans were installed in tandem i.e., one fan in front of the other fan.
It might be true if a single fan could not develop enough mass flow rate to meet its specifications. This would be true if the fans were installed side by side.
There were two fans to demonstrate the conditions of laminar as well as turbulent flow, when only one fan is on it represents laminar flow, while we turn both of the fans we consider it for turbulent flow, as in your laboratory for boundary layer experiment you will be asked to do calculations and plot the graphs for laminar as well as turbulent flow, this is the reason for having two fans.
