Abstract
Actuator disc theory and surface singularity techniques are applied to the performance of ducted fans and propellers, with particular reference to the radial clearance between rotor tips and duct inner surface and the radial distribution of rotor-blade loading. Many accounts have been written on ducted propellers but none includes the effects of clearance in any other than an approximate manner, that is, one-dimensional theory. The few studies that have been made of the radial variation in blade loading have been inconclusive and vague, mainly because of the inadequate duct model employed.
Here an accurate nonlinear theory is used to represent the duct and centrebody which has already been used successfully in the prediction of ducted propeller performance. Actuator disc theory, which is particularly suitable for combination with blade-element theory, is used to represent the variable-load propeller. Computed performance characteristics compare favourably with experimental results and the present studies enable the designer to fix both tip clearance and radial load distribution to suit the particular application under consideration. The general conclusions confirm and reinforce the limited experimental results available.
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