# Knowledgebase

Wind speed increase #199533

Asked July 15, 2014, 1:57 PM EDT

If a 5 mob wind enters a 3ft opening and exits a 1ft opening, how much will the wind speed increase?

Warren County Kentucky

## Expert Response

I think our experts need more information..Geometry of the openings and how the air is entering and leaving the openings plays a part.

BTW what is mob?

BTW what is mob?

Sorry mob should have read MPH. The front opening is a cone that funnels down to the round 1foot exit.

My thoughts on this are.

#1. The wind speed would increase in proportion to the size of the opening. using the equation for power in the wind P = 1/2*Rho*A*V^3 where P is the power in watts Rho is air density (which is close to 1 at upland sites so can be ignored) A is the swept area in M^2 and V is velocity if the wind in m/s. You could calculate the power of the wind entering and then using the smaller swept area you could calculate the wind speed at the smaller end. In short the power in the wind hitting the large surface will be the same as coming through the small surface minus any losses to friction, turbulence etc.

#2 Shrouded wind turbines usually are not the best idea as the wind hits the shroud and can become turbulent slowing the wind speed. Shrouds also limit the size of the turbine due to increase in materials.

#1. The wind speed would increase in proportion to the size of the opening. using the equation for power in the wind P = 1/2*Rho*A*V^3 where P is the power in watts Rho is air density (which is close to 1 at upland sites so can be ignored) A is the swept area in M^2 and V is velocity if the wind in m/s. You could calculate the power of the wind entering and then using the smaller swept area you could calculate the wind speed at the smaller end. In short the power in the wind hitting the large surface will be the same as coming through the small surface minus any losses to friction, turbulence etc.

#2 Shrouded wind turbines usually are not the best idea as the wind hits the shroud and can become turbulent slowing the wind speed. Shrouds also limit the size of the turbine due to increase in materials.