I have a fan which is inside a duct. When the fan is off, the pressure at the front and back of the blade remains the same. Now when it is running, the velocity of the air below will be more because fan blades induce momentum to the air. What happens to the pressures at the back and front of the blade? Will it be different?
see Fig. 4 of this reference: http://www.cibsejournal.com/cpd/2011-10/
Pressure is low just upstream of the fan and high just downstream of the fan.