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July 2, 2015


Axial position of propeller in nozzle



Is there a “best” axial position for a propeller in a nozzle?

Published information on this topic is very hard to find, but we can make some general comments. The influence of axial position of the propeller – and by this we mean the position of the blade tips – depends on whether the nozzle itself is thick or thin.

For thick nozzles (of the form that we see today), a position slightly forward of the nozzle mid-chord (e.g., no more that 5% chord) offers a very small improvement in efficiency. However, substantial loss of efficiency is seen for positions aft of mid-chord. The reason for this appears to be the beneficial application of the propeller’s low pressure zone on the forward-looking surface of the nozzle’s nose. Moving the propeller aft in the nozzle reduces the beneficial interaction. A thin nozzle (or a shroud), on the other hand, has no significant forward-looking nose surface, and a position somewhat aft of mid-chord may have a very small benefit – especially for nozzles with no diffuser angle.

Of course, you must consider the effect of axial position on tip gap. If a change in axial location increases tip gap, then there will be a corresponding loss of efficiency.

 
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Article details

Article ID: 83
Category: Other
Date added: 2015-07-02 16:13:03
Views: 342
Rating (Votes): Article rated 3.3/5.0 (26)

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