Sebastien Prothin

Study of a flexible UAV proprotor

This paper is concerned with the evaluation of design techniques, both for the propulsive performance and for the structural behaviour of a composite flexible proprotor. A numerical model was developed using a combination of aerodynamic model based on blade element momentum theory (BEMT), and structural model based on anisotropic beam finite element, in order to evaluate the coupled structural and the aerodynamic characteristics of the deformable proprotor blade. The numerical model was then validated by means of static performance measurements and shape reconstruction from laser distance sensor outputs. From the validation results of both aerodynamic and structural model, it can be concluded that the numerical approach developed by the authors is valid as a reliable tool for designing and analysing the UAV-sized proprotor made of composite material. The proposed experiment technique is also capable of providing a predictive and reliable data in blade geometry and performance for rotor modes.

Analysis of the Turbulent Wake Generated by a Micro Air Vehicle Hovering near the Ground with a Lattice Boltzmann Method

This paper presents numerical investigations undertaken to analyze the turbulent flow produced in the wake of a micro air vehicle rotor interacting with the ground. Two configurations are investigated: a free rotor and a shrouded rotor. The Reynolds number based on the chord and tip speed is Retip =0.86 × 105, which corresponds to a challenging flow where leading-edge separations are commonly observed. The numerical simulations are performed with a Reynolds-averaged Navier–Stokes approach and a large-eddy simulation (by means of a lattice-Boltzmannmethod), combinedwith an immersed boundary approach. The comparison of numerical data with measurements shows that the mean flow and the turbulent shear stresses are accurately predicted close to the ground and in the rotor wake. However, some discrepancies remain in the prediction of the rotor torque and thrust, mainly due to the difficulty to reproduce the flow near the rotor walls. An analysis is conducted to identify and understand the different sources of turbulent production. The numerical simulations show also that the presence of a shroud contributes, at a given thrust, to reduce the velocity and the turbulent intensity at the ground.

Aerodynamic Performance of a Hovering Microrotor in Confined Environment

This paper aims at understanding how the aerodynamic performance of a hovering microrotor is affected by horizontal and vertical wall proximity. Toward that end, experiments are performed to extract aerodynamic loads and velocity flow fields from strain gauges and high-definition stereoscopic particle image velocimetry measurements, respectively. The results show that horizontal wall boundary conditions contribute to enhancing aerodynamic performance, whereas vertical boundary conditions have a negligible impact. Enhancement of aerodynamic performance arises from distinct flow physics, such as rotor wake expansion or Venturi effects, that depend on the configuration considered. These results open the path toward the development of micro air vehicles dedicated to the exploration of highly confined environments.

An Application of Adaptive Blades on Convertible MAVs

A passive twist control is considered as an adaptive way to maximize the overall efficiency of a proprotor developed for convertible Micro Air Vehicles. The varied operation conditions suggest different twist distributions for hover and forward flight with the constraint of identical planform. In this work, adaption of the proprotor geometry is achieved by centrifugal force induced twist. Classical Lamination Theory is used to predict structural loads, while Blade Element Momentum Theory is employed to understand the aerodynamic benefits of adaptive proprotor as applied on Micro Air Vehicles. Tip mass is proposed to increase the stability and generate negative torsion for rotating blade. Validation of the procedure is based on measurements of blade deformation, performed by laser displacement sensors. While negative torsion is found in both rotor and propeller modes, level of deformation is still below what is required for optimum dual operation.

Performance Enhancement of Tilt-Body Micro Air Vehicle by Use of Orthotropic Laminated Proprotors

A passive twist control is considered as an adaptive way to maximize the overall efficiency of a proprotor developed for convertible Micro Air Vehicles (MAV). In this paper, adaptation of the proprotor geometry in accordance to flight configurations is achieved by induced twist generated by the inherent structural coupling effect in anisotropic composite material and centrifugal force emanating from the tip load. Beam Finite Element Model based on Rotating Timoshenko Theory is used to predict structural loads, while Blade Element Momentum Theory is employed to predict the aerodynamic performance of adaptive proprotor as applied on Micro Air Vehicles (MAV). The iterative process of combination of aerodynamic model and structural model is used to compute the steady-state deformation of the flexible laminated proprotor blade due aerodynamic loads. Finally, the optimal design of lamina blade material is carried out to investigate the potential of flexible blade in the proprotorperformance enhancement.