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Aeronautical Engineering/Centrifugal fan, wind scoop, air pressure differentials

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Expert: - 10/31/2008


Question

Rooftop wind scoop box
Hi Paul,

My questions are listed on the accompanying drawing, which shows a roof-mounted "wind scoop" box which gathers wind energy and directs it into a 6" pipe which feeds a centrifugal fan. The wind scoop box has areas of high and low air pressure as a result of wind behavior when wind meets obstructions or barriers, and my questions have to do with how those varying air pressures might enhance the amount of energy going into the centrifugal fan.  Thanks Paul,

Bob

Answer
Bob
The purpose of a ducted air system like yours is to get the airflow to the fan with as few losses of pressure head and energy as possible.  The lip on your inlet would be a high loss device because the flow will separate and go turbulent (what you are calling tumble).  Separated flow and turbulence cause high losses.  The flow should be as smooth as possible.  Getting the flow into the pipe will also cause losses.

The ducting downstream of the blower will add pressure losses that will be felt throughout the system.  It would be best if you dumped the flow to atmosphere.

Beyond that, I am dubious that a centrifugal fan can be driven this way to do meaningful work.  The fan may even try to run backwards. In any case, you should consider a proper wind turbine that is designed to be driven as your system intends.  But you might have trouble finding one that operates at your low wind speeds.
Paul
    Questioner's Rating
    Rating(1-10)Knowledgeability = 10Clarity of Response = 10Politeness = 10
    CommentThanks, Paul- Your answer helped a lot. Take care, Bob


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Paul Soderman

Expertise

Aeronautics, Fluid Mechanics, Aeroacoustics, Noise Control, Muffler Design, Wind Tunnel Research.... I know nothing about India - do not ask about schools, jobs, application requirements, career choices, etc. for India. Please, no text message verbiage; I prefer full words in full sentences. Thanks.

Experience

38 years as research engineer at NASA

Publications
AIAA, NASA

Education/Credentials
B.S. and M.S. Aeronautical Engineering - U. of Washington Graduate work Standford U.

Awards and Honors
AIAA Associate Fellow (American Institute of Aeronautics and Astronautics)

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