Aerotecnica Missili & Spazio最新文献

The contents exposed in this paper concern the CFD (computational fluid dynamics) analysis of a remote-controlled drone UAV (unmanned aerial vehicle), called Horus, under development at the Sigma Ingegneria company. Based on the drone application requests, the CFD analysis was aimed at maximizing the thrust produced and therefore, with the same power, autonomy, an aspect of importance for the use of the drone. For this purpose, being a drone with 8 counter-rotating and coaxial torque propellers, the study parameters chosen are the vertical distance between the propellers and the pitch angle of the bottom propeller. In the first part of the document, the operations necessary to prepare the geometric model and set up the numerical simulations are presented in order, carried out using stabilized finite-volume software. Subsequently, the experimental setup of tests conducted in Sigma Ingegneria is reported. In the central part, the trend of the thrust was studied as the study parameters changed. Finally, the results of tests that were conducted at the company were reported and compared with the numerical ones.

The objective of this work is to describe and validate a numerical axisymmetric approach for the simulation of hybrid rocket engines (HREs), based on Reynolds-averaged Navier–Stokes simulations, with sub-models for fluid–surface interaction, radiation, chemistry, and turbulence. Fuel grain consumption is considered on both radial and axial directions and both axial and swirl injection of the oxidizer are simulated. Firing tests of two different paraffin–oxygen hybrid rockets are considered. First, a numerical rebuilding of fuel grain profile, regression rate and pressure for axial-injected HREs is performed, yielding a reasonable agreement with the available experimental data. Then, the same numerical model is applied to swirl-injected HREs and employed to analyze both the flowfield and the regression rate variation with swirl intensity. A validation of the model through the rebuilding of small-scale firing tests is also performed.

The latest trends of Urban Air Mobility pushed the aeronautical industrial sector towards the eVTOL concept, i.e. electrical vertical take-off and landing. Electrical power, tilt-wing configuration and multiple propellers in tandem configuration, i.e. with the propellers placed one after the other, are the key features of such concept. In particular, the presence of multiple propellers working at close range introduces a new challenge: the investigation of the rotor-rotor aerodynamic interaction between front propeller slipstreams and rear propellers. This topic is rather new, thus a lack of experimental literature is noticed. The present work aims to partially fill the gap through an extensive experimental activity which investigates the main physical aspects of the phenomenon in a typical eVTOL configuration. A dedicated wind tunnel testing campaign is performed to investigate deeply the interaction between two co-rotating tandem propellers at fixed axial distance and variable lateral separation. The performance of the tandem propellers were compared with an isolated configuration both in terms of thrust and torque measurements and Particle Image Velocimetry (PIV) surveys. The experimental results are the first step in the creation of a reference database for the validation of numerical codes implemented during the design phase of such vehicles. Load measurements showed a significant loss in the rear propeller performance as a function of the overlapping ratio between the propellers. Furthermore a dedicated spectral analysis of wind tunnel thrust signals outlined high amplitude fluctuations in partial overlapping configurations. In parallel a numerical activity was performed using a mid-fidelity aerodynamic solver relying upon Vortex Particle Method (VPM) in order to enhance the comprehension of the phenomenon. The analysis of the numerical results allowed to access the flow behaviour involving the front propeller slipstream and the rear propeller disk, which is responsible of the massive losses experienced by the rear propeller.

In the framework of autonomous spacecraft navigation, this manuscript proposes a novel vision-based terrain relative navigation (TRN) system called FederNet. The developed system exploits a pattern of observed craters to perform an absolute position measurement. The obtained measurements are thus integrated into a navigation filter to estimate the spacecraft state in terms of position and velocity. Recovering crater locations from elevation imagery is not an easy task since sensors can generate images with vastly different appearances and qualities. Hence, several problems have been faced. First, the crater detection problem from elevation images, second, the crater matching problem with known craters, the spacecraft position estimation problem from retrieved matches, and its integration with a navigation filter. The first problem was countered with the robust approach of deep learning. Then, a crater matching algorithm based on geometric descriptors was developed to solve the pattern recognition problem. Finally, a position estimation algorithm was integrated with an Extended Kalman Filter, built with a Keplerian propagator. This key choice highlights the performance achieved by the developed system that could benefit from more accurate propagators. FederNet system has been validated with an experimental analysis on real elevation images. Results showed that FederNet is capable to cruise with a navigation accuracy below 400 meters when a sufficient number of well-distributed craters is available for matching. FederNet capabilities can be further improved with higher resolution data and a data fusion integration with other sensor measurements, such as the lunar GPS, nowadays under investigation by many researchers.

Deep-space CubeSats missions require careful trade-offs on design drivers such as mass, volume, and cost, while ensuring autonomous operations. This work elaborates the possibility of off-loading the reaction wheels without the need of carrying a bulky and expensive reaction control system or the field-dependent magnetotorquers. The momentum accumulated along two body axes can be removed by either offsetting the main thruster with a gimbal mechanism or by tilting differentially the solar wings. The dumping on the third axis can be still accomplished by imposing a specific attitude trajectory with the motion of either the gimbal or the arrays drive mechanism. The M-Argo CubeSat is selected as case study to test the techniques along its deep-space trajectory. The strategies decision-making is autonomously carried out by a state machine. The off-loading during the cruising arcs employs the gimballed thruster and takes typically 3 h, granting a mass savings of more than 99% with respect to the usage of a reaction control system. The trajectory is shown to have negligible differences with respect to the nominal one, since the thrust is corrected accordingly. During the coasting arcs, the solar arrays are tilted and several hours are required, depending on the Sun direction and intensity, but the propellant is completely saved. Sensitivity analyses are also carried out on the initial angular momentum components and the center of mass displacement to check the robustness of the algorithms.

In this study, a theoretical and numerical framework for simulating transcritical flows under a variety of conditions of interest for aerospace propulsion applications is presented. A real-fluid multicomponent and multiphase thermodynamic model, based on a cubic equation of state (EoS) and vapor–liquid equilibrium (VLE) assumptions, is presented to describe transcritical mixtures properties. The versatility of this thermodynamic model is reported since it can represent at the same time the supercritical states as well as subcritical stable two-phase states at equilibrium, via a homogeneous mixture approach. The effect this model has on the evaluation of the thermophysical variables will be emphasized. From the Computational Fluid Dynamics (CFD) point of view, the well-known numerical challenges that arise with the coupling between real-fluid thermodynamics and governing equations under transcritical conditions, are addressed by comparing a fully conservative (FC) to a quasi-conservative (QC) numerical schemes, in the context of the advection problem of a transcritical contact discontinuity.