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International audience; In recent years, unmanned aerial vehicles applications have grown in various fields. New design configurations have emerged to address these needs. This paper focuses on the multidisciplinary design optimization of three popular concepts of drones under a common framework: multicopters, fixed-wings, and the more recent fixed-wing VTOLs. Low-fidelity but computationally efficient models for drone sizing are proposed, some of them being shared by the different concepts. The models are integrated with a design optimization approach, and an efficient sizing methodology allows for reducing the problem complexity. This approach is instrumental because of the large number of design variables and constraints involved in the multidisciplinary design process. Examples of sizing results are provided to validate the methodology for fixed wing UAVs. In addition, a study case demonstrates the benefit of a common framework for comparing the performances of different drone concepts. A key finding is that the VTOL propulsion of the fixed-wing VTOLs must be carefully optimized to avoid an undesirable mass penalty.

Two separate experiments are conducted on a three bladed NACA0012 rotor operating at low Reynolds numbers using phase-locked infrared thermography coupled with simultaneous force and torque measurements. The first, focuses on the effects of freestream turbulence on boundary layer transition over the suction side of the aerofoil of the rotor in an advancing configuration. Freestream turbulence (FST) was generated in an open section wind tunnel using grids and was characterized using Hot-Wire anemometry. In general, when the rotor was subjected to FST, an increase in thrust and efficiency was observed, which could be due to the FST suppressing flow separation or by inducing early transition. The second experiment, consisted of a parametric study on the impact of forcing boundary layer transition using roughness placed on the suction side of the aerofoil, in a hover configuration. The height of the roughness was varied from 52-220μm and was placed at all at at 10% chord, over the entire span of the blade. Force and torque measurements revealed that there could be a optimal roughness height that could lead to a performance increase.

International audience; The number of applications that use multirotor drones has significantly increased in the past year due to their high manoeuvrability and capability to perform hovering. The main limit of such configuration is its endurance especially when batteries are used as the energy source. This paper focuses on the evaluation of the endurance of multirotor drones in forward flight using a design optimization approach. Lightweight models to represent accuratly the physics of forward flight are proposed. One significant finding is that the design optimization code enables to rapidly obtain a design for a given set of requirements and has been validated on the Parrot ANAFI USA. The end of the article illustrates the sensitivity of maximum takeoff weight to the drag of aerodynamic frame.

The present work outlines efforts at ISAE-SUPAERO to reduce the acoustic footprint of rotors operating at low Reynolds and low Mach numbers typical of small and medium scale drones. An experimental campaign that aims at characterizing rotor noise is presented. The latter serves as a basis for validation of numerical approaches and to investigate the noise mechanisms. Data are obtained in an anechoic room with dimensions (wedge tip to wedge tip) 5.02x5.24x5.34 m3 and cut-off frequency 80 Hz. Aerodynamic loads as well as acoustic fields are recorded for two off-the-shelf (APC 9x6 SF and 11x4.7 SF) and four canonical rotors with different numbers of blades. Both near and far acoustic fields are measured using one microphone located one diameter away from the rotor plane and 13 microphones mounted on a directivity antenna. A range of rotation speed from 1,000 to 10,000 RPM is addressed, corresponding to Mach and Reynolds numbers up to 0.23 and 130,000 respectively. Results presented in this article are related to two-bladed rotors and are validated using existing experimental data from the literature. They are then used to assess in-house numerical simulations (NL-VLM and CFD) and unravel the physics behind rotor noise at low Reynolds and low Mach numbers. This fundamental understanding will help draw general guidelines for the design of low noise rotors.

International audience; This paper presents a numerical and experimental investigation of the aerodynamic characteristics of a vertical take-off and landing micro air vehicle designed to fly in the Martian atmosphere. Numerical tools are validated through experimental data from the literature where Martian conditions are replicated. An innovative airfoil is designed for the specific flying conditions of the Martian MAV, i.e. compressible and ultra-low Reynolds number flows. This airfoil is evaluated in different Reynolds and Mach number conditions using unsteady compressible laminar Navier-Stokes simulations. Single rotors and coaxial configurations are designed for different thrust constraints by optimizing the chord and twist distributions using a free wake lifting line method. Rotors are firstly evaluated numerically using Navier-Stokes simulations. To validate the simulations, the optimized configurations are tested experimentally in an evacuation chamber, recreating Martian atmosphere in terms of density and gas. Thrust and torque on each rotor are measured by a two-component set-up. Tests are performed up to transonic flow conditions at blade tip. Results are extrapolated to a suggested design for a Martian MAV.

International audience; An experimental investigation on the flow topology and performance of a rotor operating at low Reynolds numbers is presented. The feasibility of laminar to turbulent transition experiments over small rotors is demonstrated. Phase-locked infrared thermography coupled with simultaneous force and torque measurements were used to study a three bladed NACA0012 rotor with a radius of 0.125 m and an angle of attack of 10 degrees. Boundary layer transition was fostered using two-dimensional (2D) and threedimensional (3D) isolated roughness elements, placed at approximately 5% and 28% of the rotor blades chord. In the smooth rotor configuration, a 3D flow topology is observed, consisting of a clear laminar region closer to the blade root and a turbulent region at the blade tip. It was found that the state of the boundary layer can significantly affect the rotor’s performance, with the forcing of laminar to turbulent transition generally resulting in a loss of performance when compared to the smooth reference rotor case.

International audience; This paper presents a numerical and experimental study of the aerodynamic characteristics of a vertical takeoff and landing (VTOL) micro air vehicle (MAV) designed to fly in Mars' atmosphere. Numerical tools are validated through experimental data from the literature where Martian conditions are replicated. Innovative airfoils are designed for the specific flying conditions of the Martian MAV, i.e. compressible and ultra-low Reynolds number flows. An optimized airfoil is evaluated in different Reynolds and Mach number conditions using unsteady laminar Navier-Stokes simulations. Rotors are designed by optimizing the chord and twist distributions using a free wake lifting line method with different geometrical and lift constraints. Rotors are numerically evaluated using two different Navier-Stokes solvers. A coaxial configuration is also defined to achieve zero total torque and double lift. To validate the simulations, experiments are performed in the ONERA's low pressure tank, recreating Martian atmosphere in terms of density and gas. Thrust and torque are measured by a two-component setup developed by ISAE-SUPAERO, with independent measures on each rotor in coaxial configuration. Tests are performed up to transonic flow conditions at blade tip.

International audience

International audience; In order to better predict the risk induced by orbital debris during their atmospheric re-entry, phenomena in the “shadow region” of the debris, i.e. the region that is not directly impinged upon by the freestream flow, were investigated. Four types of flow were shown to cause significant values of heat flux in the shadow region, for continuous hypersonic hyperenthalpic incoming flow conditions : attached flow, detached flow with fluid or solid reattachment, and shock-shock interactions. Models for pressure and heat flux distributions resulting from attached flows on cylinders leeward side were realized using Proper Orthogonal Decomposition interpolation.

International audience; In the advent of electrical vertical take-off and landing aircraft development, a fast approach to predict variationof propeller axial and off-axis aerodynamic loads at large incidence angle has been desired. This paper presentedan analytical approach obtained by a simplified blade element method considering local blade section conditions.The theory has been further validated against available experiments for propeller at high incidence conditions, and was found applicable to a wide range of geometries and operating conditions.

International audience; A detailed experimental study of propeller-wing interaction was presented. Five-hole probe was used to obtain velocity distribution at a survey plane behind trailing edge of a high-aspect-ratio wing with tractor propeller. Significant deformation of propeller slipstream was observed compared to a free propeller. The deformation was more prominent at low advance ratio, where transition flight of vertical take-off / landing aircraft were concerned. Comparison with two recent reduced-order slipstream models revealed large discrepancies between theoretical predictions and wake survey results. An analytical model of slipstream transverse deformation was proposed at the end that might be incorporated into improve such models.

A flight control system is configured to control the flight of a convertible fixed-wing drone (12), having two left and right wings, each supporting a propeller in front and a deflection flap at the rear edge. The control system includes an attitude regulator (154) of the drone (12) to respectively control the roll angles ϕm, pitch θ m and yaw Ψm, measured by one or more sensors on setpoint angles ϕd, pitch θ d and lace Ψd. The first attitude regulator (154) comprises a first MFC SISO device (162) for modelless control at one input-one output for regulating and controlling the pitch angle θ m measured on the pitch set angle θ d by determining a first command δn for symmetrical deflection of the left and right flaps, applied with the same sign to said left and right flaps., Un système de contrôle de vol est configuré pour contrôler le vol d'un drone convertible à voilure fixe (12), ayant deux ailes gauche et droite supportant chacune une hélice en avant et un volet de déflexion en bordure arrière. Le système de contrôle comporte un régulateur d'attitude (154) du drone (12) pour asservir respectivement les angles de roulis ϕm, tangage θ m et lacet Ψm, mesurés par un ou plusieurs capteurs sur des angles de consigne de roulis ϕd, tangage θ d et lacet Ψd. Le premier régulateur d'attitude (154) comporte un premier dispositif MFC SISO (162) de commande sans modèle à une entrée-une sortie pour réguler et asservir l'angle de tangage θ m mesuré sur l'angle de consigne de tangage θ d en déterminant une première commande δn de déflection symétrique des volets gauche et droit, appliquée avec le même signe sur lesdits volets gauche et droit.

International audience