Assessment of low-fidelity fluid–structure interaction model for flexible propeller blades

Low-fidelity fluid–structure interaction model of flexible propeller blades is assessed by means of comparison with high-fidelity aeroelastic results. The low-fidelity model is based on a coupled extended blade-element momentum model and non-linear beam theory which were both implemented in Matlab. High-fidelity fluid–structure interaction analysis is based on coupling commercial computational fluid dynamics and computational structural dynamics codes. For this purpose, Ansys CFX^® and Ansys Mechanical^® were used. Three different flexible propeller blade geometries are considered in this study: straight, backward swept, and forward swept. The specific backward and forward swept blades are chosen due to their aeroelastic response and its influence on the propulsive performance of the blade while a straight blade was selected in order to serve as a reference. First, the high-fidelity method is validated against experimental data available for the selected blade geometries. Then the high- and low-fidelity methods are compared in terms of integral thrust and breaking power as well as their respective distributions along the blades are compared for different advancing ratios. In a structural sense, the comparison is performed by analyzing the blade bending and torsional deformation. Based on the obtained results, given the simplicity of the low-fidelity method, it can be concluded that the agreement between the two methods is reasonably good. Moreover, an important result of the comparison study is an observation that the advance ratio is no longer a valid measure of similarity in the case of flexible propeller blades and the behavior of such blades can change significantly with changing operating conditions while keeping the advance ratio constant. This observation is supported by both high- and low-fidelity methods.