The aim of Rotorcraft Aerodynamics Lab is to develop research activities in the topical subjects of helicopter and e-vtol aerodynamics and aeroacustics, making use of both the numerical simulation and the experimental activity.

ONGOING ACTIVITIES

The in-house developed code ROSITA (Chimera based Navier-Stokes solver) is continuously under development in order to enlarge its capabilities and efficiency. Recently a vorticity confinement approach have been intriduced in the code to improve the aerodynamic and aerocoustic predictions of vortex dominated flows, in particular helicopter rotor flows featuring Blade-Vortex Interaction (BVI). Noise propagation makes used of the permeable surface FFWH formulation with retarded time or emission surface approaches.
The open-source SU2 code was extended at DAER for rotor performance prediction in hover and forward flight. The core of the code is the set of U-RANS equations, which are solved to determine the flow. Hover simulations can be performed using a rotating reference frame. A multizone approach is used to simulate the interaction between rotors/propellers, with rotating regions communicating through sliding interfaces where a weighted interpolation is needed. The farfield propagation of the tonal noise is computed with a permeable surface FWH formulation implemented with a modular CFD-CAA style. The formulation is used to study the acoustic interaction between propellers in forward flight and hover with different relative positions. SU2 can also compute the quadrupole source using a synthetic turbulence strategy called Stochastic noise generation (SNG). A multidisciplinary adjoint solver based on algorithmic differentiation is implemented for the coupled RANS-FWH. This framework adopts a steady optimization chain even if the noise emission is intrinsically unsteady. The obtained sensitivity is used to modify the shape of blade propellers to obtain a new local minimum with lower SPL without losing aerodynamic performance.
An other computational tool that is continuosly under development is the mid-fidelity code DUST, initially developed in the frame of a collaboration with A3 by Airbus and released under MIT license (open source). The code, characterized by the implementation of an efficient vortex particle method for the wake simulation, was recently coupled with the multibody software MBDyn to perform aeroelastic simulation of complex rotorcraft vehicles. DUST was deeply used for the aerodynamic characterization of interactional aerodynamics typical of eVTOL aircraft and tiltrotors and was coupled with the multibody software MBDyn to perform aeroelastic simulation of complex rotorcraft vehicles.

The interactional aerodynamics and aeroacustic of multi-rotors systems has been recently investigated also by wind tunnel experiments. An experimental test rig made by two small propellers equipped with strain gauge balances was designed and manufactured for the investigation of aerodynamic interactions between propeller-propeller and wing-propeller. The experimental campaigns performed at “S. De Ponte” wind tunnel (in the departmental aerodynamic lab) provided a comprehensive database including stereoscopic PIV surveys that was useful for the validation of CFD tools with different levels of fidelity. The test rig was also used for the aeroacoustic characterization of the foorprint provided by tandem propellers reproducing typical hover conditions of eVTOL aircraft.The strong interference of two propeller quite close each to the other was tested in the “De Ponte” wind tunnel in the departmental aerodynamic laboratory. Furthermore a system composed of a main rotor and two propellers (compund helicopter configuration) has been widely tested in the GVPM (the large wind tunnel of Politecnico) in the frame of GARTEUR AG25 project.
From a more fundamental point of view an investigation of 2D parallel BVI is going on both by experiments with two airfoil models and with LES simulations using the open-access compressible DG solver FEMilaro.

FUTURE PLANS

Work is in progress to couple the CFD code ROSITA with a vortex blob representation of the rotor wake. The adopted formulation for the vortex particle wake has been derived from that implemented in the DUST code and tightly coupled with the CFD near field calculation. This approach, aimed at improving the resolution of the wake representation, will be extended to multi-rotor configurations featuring strong wake interactions.
The coupling with the multibody software MBDyn to consider the structural deformation is under development for the SU2 solver too.
A new Garteur activity on the analysis and decomposition of the aerodynamic force acting on rotary wings has very recently started within the AG27 group. Several approaches to decompose the drag force (thermodynamic, Lamb vector, exergy, partial pressure) will be assessed for unsteady flows, considering a rotating reference frame. The requirements needed to apply these methods to the numerical solutions, achieved with the ROSITA and SU2 codes, will be clarified and cross-correlation of the different approaches will be attempted.

The experimental test rig for propellers interaction investigation will be used to perform wind tunnel tests reproducing the conversion manoeuver of an eVTOL aircraft. Moreover, the propellers models are planned to be integrated with a semi-span-wing to perform wind tunnel test campaigns aimed at the evaluation of benefits and drawbacks of distributed propellers configurations for eVTOL applications. Moreover, the test rig will be used in the frame of the GARTEUR project AG26, now ongoing and aimed to the investigation of aeroacoustics of multirotor configurations. In this framework, a comprehensive experimental database concerning side-by-side and tandem propellers configuration will be produced in POLIMI facilities for both the aerodynamic and aeroacoustic performance. The database will be useful for the validation of numerical codes by the project partners. In particular, a multi-fidelity approach to aeroacoustics proposed by POLIMI based on the use of DUST and SU2 aerodynamics softwares coupled with a FWH code will be validated in this framework.

ERC KEYWORDS

• PE6_12 Scientific computing, simulation and modelling
• PE8_1 Aerospace Engineering
• PE8_4 Computational Engineering
• PE_5 Fluid Mechanics

FREE KEYWORDS

• Blade-Vortex-interaction
• Rotary-wing aircraft
• Wind tunnel testing