Abstract
The presence of conservative forces on rotor blades is neglected in the blade element theory and all the numerical methods derived from it (like e.g. the blade element momentum theory and the actuator line technique). This might seem a reasonable simplification of the real flow of rotor blades, since conservative loads, by definition, do not contribute to the power conversion. However, conservative loads originating from the chordwise bound vorticity might affect the tip vortex trajectory, as we discussed in a previous work. In that work we also hypothesized that this effect, in turn, could influence the wake induction and correspondingly the rotor performance.In the current work we extend a standard actuator line model in order to account for the conservative loads at the blade tip. This allows to isolate the influence of conservative forces from other effects. The comparison of numerical results with and without conservative loads enables to confirm qualitatively their relevance for the near wake and the rotor performance. However, an accurate quantitative assessment of the effect still remains out of reach due to the inherent uncertainty of the numerical model.
Highlights
The study of the fluid mechanics of propellers dates back to the 19th century
The blade element theory, which is attributed to Drzewiecki [3], takes the rotor geometry into account by dividing each blade into a finite number of independent lifting surfaces, it does not define any limit to the propeller efficiency
As we described in our previous work [12], the origin of the conservative force is the Kutta-Joukowski load acting on the chordwise bound circulation Γchord, which is defined as the circulation around a contour normal to the blade chord
Summary
The study of the fluid mechanics of propellers dates back to the 19th century. Rankine [1] and Froude [2] settled the basis of the momentum theory explaining the origin of propeller thrust and torque from the momentum change in the fluid. The blade element theory, which is attributed to Drzewiecki [3], takes the rotor geometry into account by dividing each blade into a finite number of independent lifting surfaces (blade elements), it does not define any limit to the propeller efficiency. This limitation is owed to the lack of consideration of the velocity induction of the propeller itself. It is worth remarking that only fluid loads contributing to the power conversion
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