Propeller blade design thickness and blockage issues due to source-induced factors
Hunt, David S.
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A propeller lifting-surface design and analysis program is improved upon by implementing enhancements in the source distribution calculation to represent the blade thickness. It is recognized that the present method of setting the source line distribution representing blade thickness (currently based on linearized slender-body theory for an isolated foil section) may introduce significant errors. This is the case for propulsors with a combination of a large thickness/chord ratio (blockage effect) and numerous blades (cascade effect). A source panel (area) method was developed to more accurately model these effects. This method uses the lattice structure of the current PBD-14 code from which to compute the source-induced velocity factors between the blades, hub, and duct, if present. Using the method of images allows the hub and duct to be modeled as panel images from the blade panels. The source-induced effects of the whole propulsor are accounted for by using a panel method to obtain a source distribution along the mean camber surface of the blade. Invoking the kinematic boundary condition on the true blade suction and pressure surfaces solves this system of linear equations, which represent the blade thickness distribution. This robust formulation assigns source strengths more accurately over a much larger range of thickness/chord ratios and increasing numbers of blades, as evidenced by a more accurate velocity streamline trace representation of the actual pressure and suction side surfaces of the blade. Experimental validation is demonstrated for open and ducted flow stators.
NPS CIVINS (Civilian Institutions) Thesis document
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