Rice nozzle confusion

Discussion in 'Propulsion' started by Frog4, Oct 11, 2011.

  1. Frog4
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    Frog4 Proletariat

    working out increased efficiency on a prop, and wondering why the losses at higher speed vs lower speed in rice nozzles? Looking at jet engines on aircraft, are they losing the same because of drag?
     
    Last edited: Oct 11, 2011
  2. waikikin
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    waikikin Senior Member

    I'd say the extra drag at speed, the nozzles seem to be preferred for slow & heavy vessels such as tugs & trawlers. I think "Rice" is a "brand" of nozzle profile, the marketing seems to infer that the nozzle is a percentage part of the propulsion, dunno if thats true, some one who really knows the propulsion game will. Here is a pair of Rice profile nozzles I fitted up to a self propelled barge........................ http://www.boatdesign.net/gallery/showphoto.php/photo/11472/ppuser/12438 ............. http://www.boatdesign.net/gallery/showphoto.php/photo/11475/ppuser/12438 ............. http://www.boatdesign.net/gallery/showphoto.php/photo/11476/ppuser/12438

    All the best from Jeff.
     
  3. baeckmo
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    baeckmo Hydrodynamics

    To make it short: Yes (you never see a nozzle on a fighter jet)
     
  4. powerabout
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    powerabout Senior Member

    woudnt that be yes because the big fan is inside a housing?
    as for the propulsor ( jet engine) it wouldnt work if it wasnt in a housing
     
  5. powerabout
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    powerabout Senior Member

    be careful when using the term efficient when talking props
    efficient at what?
     
  6. Frog4
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    Frog4 Proletariat

    there is a difference in a RICE SPEED NOZZLE and KORT NOZZLE

    Rice speed nozzles have almost the same cross section as a jet engine housing, identical aero-dynamics ...

    does the jet engine suffer the same drag problems at high speed as the rice speed nozzle?
     
  7. Frog4
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    Frog4 Proletariat

  8. Yellowjacket
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    Yellowjacket Senior Member

    It isn't quite the same.

    In a turbofan engine the fan diameter is substantially reduced (compared to a similar power open propeller or propfan) and the blade count is increased. If the blades didn't have a shroud the tip losses would kill the efficiency. The inlet of the fan is designed to match the airflow at high speed and is smaller than the fan tip. This allows the air to slow down as it enter the fan when you are at cruise. As the aircraft goes to high speed, the required fan airflow comes into line with the airflow passed by the inlet. At low speed the fan efficiency is better than a turbojet, but it isn't as good as a prop.

    Propulsive efficiency is based on the differece between the speed of the vehicle and the speed of the acclerating flow that is creating the thrust. Moving more air at a lower velocity difference gives you high efficiency. At high speed (and altitude) the fan becomes efficient. This happens at higher velocities where the compressibility effects of air come into play (the fan blade tips are in the transonic range and flow velocity out the back end of a turbofan nearly sonic).

    These "nozzles" reduce tip losses and provide more thrust at low speed than if the nozzle wasn't there. But the tip shroud ring results in a large drag increment at high speeds that is unacceptable.

    You could do the same thing as these nozzles by putting a ring around a typical small airplane propeller and the results would be much the same, it would provide more low speed thrust and have higher drag at higher speed. There was an airplane that used a shrouded prop, it was called the Fantrainer, and it had a much smaller higher speed fan in a shrouded ring in the aft fuselage. It worked fine, but wasn't as efficient as an open prop.
     
  9. Frog4
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    Frog4 Proletariat

    thanks Yellowjacket ...

    I was looking at just rings or prop guards ... studying the rice speed nozzle patent, he gave some numbers for prop clearance and nozzle depth in proportion to prop diameter ... they seem very tight ... .040" prop clearance for my application ...
     
  10. powerabout
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    powerabout Senior Member

    anything you put in the water will kill speed so forget it
    There was an experiment with a modern hi bypass jet with an unshrouded high speed prop that was better then a conventional shrouded bypass fan as they all are now, and it was way more efficient but they decided the consumer would not like it
     
  11. Frog4
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    Frog4 Proletariat

    It is for an electric TUGBOAT build, "speed" is not what we are looking for ...

    You would happen to have any links to that "experiment" would you???
     
  12. powerabout
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    powerabout Senior Member

    1 person likes this.
  13. Frog4
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    Frog4 Proletariat

    thanks powerabout ...

    what I find perplexing is that ALL of those were shelved because of "lower fuel prices" yet all the PoC's proved out a 30% reduction in fuel consumption.

    WHY O WHY WOULD THEY SHELVE THEM???? That is 30% more MONEY in their pocket ... retarded backward @#$ thinking ...
     

  14. Yellowjacket
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    Yellowjacket Senior Member

    The propfan worked, but it made more noise. The airlines pass on fuel cost to the customer. So long as all the airlines have the same equipment they would be competitive. The customers would rather have a more comfortable trip than save $15 on each leg of a trip. The airlines were more concerned that the customers wouldn't accept the higer noise for a small reduction in air fares.

    Note that Pratt & Whitney is developing a larger "geared" fan that runs at lower speeds and provides better propulsive efficiency and is more quiet than regular fans and a lot more quiet than propfans.
     
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