Travail de fin d'études et stage[BR]- Travail de fin d'études : Blade Element Momentum Theory extension for the modelisation of a contra-rotating rotors drone[BR]- Stage d'insertion professionnelle

Abstract

This thesis focuses on the study, the development and the implementation of a model for coaxial, contra-rotating rotors based on the Blade Element Momentum Theory (BEMT ) in order to predict the performances of an operating coaxial drone and to optimise its configuration such that it minimises the power consumed.

The implemented BEMT (commonly used in the development of turbomachinery) describes completely the airflow through the rotor from the far upstream to the far downstream by providing the velocity triangles and the local aerodynamical variables in the rotor surrounding. It significantly improves the understanding of the variation of the rotor performances and how the tuning of the control parameters such as the rotor rotation speed or the blade collective pitch angle play an essential role in the optimisation of the coaxial drone rotor.

At first, the simulations results are validated for the isolated rotor case by contrasting them with benchmark experiments from the literature and with experimental measurements realised on a drone test bench and provided by the industrial promoter of this thesis. The outcomes shows a good agreement with the actual drone operation and even better when considering additional correction factors such as the Prandtl loss factor or the induced power factor. In fact, the performances graphics are depicted and analysed. These consists in the variations of thrust, the mechanical power with respect to the rotor rotation speed and the power loading evolution as function of a given thrust. The thrust and power predictions revealed a favourable adaption to the tuning of the collective pitch angle accounting for a one-degree of accuracy on the angle. While the power loading (and thus the rotor propulsive efficiency) increases with the blade length. Furthermore, it is demonstrated that an increase of the blade collective pitch angle from 2° to 3° is required in order to enhance the matching between the predictions and the experimental measurements. Since the one-degree of accuracy on the blade collective pitch angle can not explained this deviation, it is supposed that the error comes from an issue in the fixing mechanism of the blade.

Subsequently, the experimental operating data measured on a drone prototype are used to analyse and to validate the predictions of the coaxial model. The simuilations outcomes allows to feature the interest in the upper rotor wake contraction application and especially, the consideration of the rotors axial separation distance in the model implementation. As a matter of fact, the consideration of the wake constriction of the upper rotor slipstream shows a reduction of 10% to 20% of the relative errors measured on the lower rotor mechanical power predictions with respect to the measurements data. Nonetheless, erroneous predictions of the mechanical power at the upper rotor are still indicated. It is supposed that it stems from the non-consideration of the adverse influence of the lower on the upper rotor.