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Ducted Fan Propulsor/Generator

  1. Nov 24, 2007 #1
    So I'm working on a thesis project at the moment designing an airship, and I've run into a bit of a stumbling point.

    I'm wondering if it would be possible to have a propeller that works to produce propulsive power when it needs to fly, but when the craft is tethered could operate as an electricity-generating wind turbine. The electrical system is definitely capable of it, but what I'm unsure about are the mechanicals (i.e. the gearbox and operational rpm ranges for both different applications), and more importantly the aerodynamics.

    I've read that ducted fans are more efficient for propulsion, but to be honest, I'm not exactly sure why. Obviously the effects of the duct on the aerodynamic flow around the propeller would have a big impact on the efficiency of it as a generator, and I'm not sure whether they would be positive or negative.

    I have some reading to do on actuator disc theory and fluid dynamics, but I must say I'm in over my head (I'm an industrial designer, not an engineer, by trade, so this entire thesis has been a serious crash course in the fun math and physics side of things).

    At the moment I'm not too overly concerned about the specifics so much as a basic idea of whether or not it's feasible.

    I greatly appreciate any help, and thanks in advance!
     
  2. jcsd
  3. Nov 25, 2007 #2
    an airship needs to be light weight
    batterys are heavy
    so I fail to see a big gain from electricity-generating wind turbine

    but a ducted fan could make power
    the main gain is from reduced tip drag votex drag
    vairable pitch props should solve the gear/rpm problem
     
  4. Nov 25, 2007 #3
    Thanks for the reply.

    Instead of using heavy batteries as accumulators, the plan is to use a hybrid H2-air fuel cell/supercapacitor system to smooth out the input from solar cells and the wind turbine before it goes to the inverter. If hydrogen is used as the lift gas, then there's an ample supply for the fuel cell, and it can be over-inflated at tethered altitudes to provide enough buffer capacity, since it doesn't need the additional air volume in the ballonets to provide the pressure height (which should free up about 10% of the available internal volume...that's huge).

    Variable pitch props make sense. My only real concern was whether the actual duct design would be dramatically different for use as a propulsor or as a generator. But from what I've been able to find, they both use a roughly airfoil-shaped profile - ducted wind turbines have a much more significant flare towards the outlet, but I think that might partly be because drag isn't a factor on a static turbine.
     
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