Computational aeroacoustics of rotor noise in novel aircraft configurations

Abstract

The accurate and reliable prediction of the aerodynamic noise sources of open rotors and ducted-fans in electric Vertical Take-Off and Landing (eVTOL) and non-conventional aircraft configurations is a challenging task from a computational perspective. Indeed, such propulsive systems can often operate in highly distorted and non-homogeneous flows, with the rotating blades interacting with strongly non-uniform and turbulent flows; and/or experience phenomena related to low Reynolds numbers and boundary-layer transition, due to the relatively small diameters and blade tip speeds. While analytical, semi-empirical and low-fidelity numerical models can provide quick and computationally inexpensive predictions, their results are often not fully reliable and their state-of-the-art requires a further development step to properly address the problem of rotor noise prediction in non-conventional aircraft and rotorcraft. On the other hand, Navier-Stokes based scale-resolving approaches such as Large Eddy Simulation (LES) have the capability to capture most of the aforementioned phenomena, but at a prohibitive computational cost for a routine employment in the design stages of such innovative vehicles. In view of this, high-fidelity scale-resolving lattice-Boltzmann (LB) numerical simulations, coupled with the Ffowcs Williams & Hawkings' (FW-H) acoustic analogy, are extensively performed and validated in this thesis. A wide range of aeroacoustic problems, spanning from airfoil and small-scale propellers in transitional boundary-layer regime to open rotors in blade-vortex interaction conditions and ducted fans ingesting the airframe turbulent boundary-layer, are addressed with the aim of predicting, identifying and characterizing and the primary sources of aerodynamic noise associated to open rotors/propellers and ducted-fans in eVTOL and novel aircraft configurations by means of the hybrid LB/FW-H approach.