Assessment of a Mid-Fidelity Numerical Approach for the Investigation of Tiltrotor Aerodynamics

Abstract

The study of the complex aerodynamics that characterise tiltrotors represents a challenge for computational fluid dynamics tools. URANS numerical solvers are typically used to explore the aerodynamic features that characterise the different flight conditions of these aircraft, but their computational cost limits their applications to a few vehicle configurations. The present work explores the capabilities of a new mid-fidelity aerodynamic code that is based on the vortex particle method, DUST, to investigate the performance and flow physics of tiltrotors. With this aim, numerical simulations were performed in DUST while considering XV-15 tiltrotor configurations with increasing complexity. The study started with the investigation of a simpler configuration made up of a single wing and a proprotor. Subsequently, the full aircraft was studied in steady-level flights and its major operating flight conditions were explored—i.e., hover, conversion phase, and cruise. A thorough assessment of the code capabilities was performed by the comparison of the numerical results with high-fidelity Computational Fluid Dynamics (CFD) data. This thorough comparison showed that the mid-fidelity numerical approach implemented in DUST is suitable for capturing the flow physics related to the complex aerodynamic interactions between the proprotors and the wing along with the entire flight envelope of the tiltrotor. Moreover, a good representation of the aerodynamic performance of the vehicle was obtained, particularly for the flight conditions that are characterised by limited flow separations. The good accuracy obtained for both the performance and flow physics, combined with the relatively lower computational costs required by the mid-fidelity solver with respect to the URANS simulations, indicates that DUST could be considered a valuable tool for use in the preliminary design of novel tiltrotor configurations.

Unsteady flow behaviour of multi-rotors in ground proximity

“…When the image plane was removed, the height of the fountain increased and it was shown to drift laterally resulting in ‘re-ingestion switching’. These results were also found in a numerical study by Zanotti, Savino, Palazzi, Tugnoli, and Muscarello (2021). The occurrence of this phenomenon is reported to be aperiodic (Polak et al., 2000) at a rate 1–2 orders of magnitude lower than the rotational frequency of the rotors (Potsdam & Strawn, 2005).…”

Dynamic Modeling and Analysis of Tilt-Wing Electric Vertical Take-Off and Landing Vehicles

“…• Large flight envelope due to transformation This seems to be the reason that, despite research efforts in tilt-wing VTOL aircraft and convertiplanes since mid of the 20 th century [4,11,22,23], no established aerodynamic model exists. Indeed, propelled by diverse tools for fluid simulation, increased efforts have been made lately to understand the intricate aerodynamics of tilt-wing and multirotors in general [8,16,[24][25][26]. In accordance with this trend, finding a representative aerodynamic model can be identified as the most demanding challenge for the work on tilt-wing aircraft, especially from a flight control perspective when considering the transition maneuver.…”

Coupling Mid-Fidelity Aerodynamics and Multibody Dynamics for the Aeroelastic Analysis of Rotary-Wing Vehicles

“…In detail, the flow field representation for C.III clearly shows the interference of the proprotor helical system with the wing. This interaction mainly provides an up-wash due to the blade tip vortex encountering the inboard region of the wing [37] and a consequent local increase of pressure with respect to C.I and C.II, as shown by the larger and more intense pressure region computed over the wing surface for the aircraft configuration equipped with proprotors (see Figure 21c). Figure 22 compares the pressure coefficient C P distribution evaluated at the mid-span section of the flaperon.…”

“…No convergence studies were performed for the full vehicle coupled simulation. Indeed, the choice of the selected spatial and time discretizations for the full vehicle was dictated by best practices (see Reference [37]) and by the will to limit the computational effort of the simulations. Indeed, one of the goals of the present activity is to show the capabilities of the novel coupled numerical tool for the preliminary design of innovative rotary-wing aircraft configurations that requires a wide number of numerical simulations to reproduce the different attitudes of their flight mission.…”

“…Moreover, a VPM method was implemented for wake modeling providing a stable Lagrangian description of free-vorticity flow field, which is suitable for numerical simulations of configurations characterized by strong aerodynamic interactions. DUST was thoroughly validated by comparison with both high-fidelity CFD simulations results and experimental data over complex rotorcraft configurations, such as eVTOLs [36] and tiltrotors [37]. Consequently, this novel open source tool is reaching maturity for the simulation of the aerodynamics of complex rotorcraft configurations accurately reproducing the interaction between rotors and wings.…”