Noise shielding simulation of a UAV drone using a coupled DG / fast BEM

Abstract

The primary focus of our research is on the strong coupling of two advanced Computational Aero-Acoustic (CAA) methods for performing efficient fan tone shielding simulations of unmanned aerial vehicles (UAV) with highly integrated propulsion systems. In particular, the Fast Multipole Boundary Element Method (FM-BEM) which can solve a surface integral based on the Kirchhoff-Helmholtz wave equation is combined with a volume resolving Discontinuous Galerkin (DG) method which is very well suited for the intake duct where strong mean flow gradients are present. The Möhring-Howe acoustic analogy is used during the backward data exchange process for derivation of acoustic velocities in presence of a mean flow.Applying CAA to assess UAV configurations is novel, since acoustics in general comes as a by-product when the configuration is already fixed. There is, however, a technological interest in determining whether the application of rapid turnaround CAA techniques can enhance the capabilities in terms of low noise mission planning, minimising the risk of early acoustic detection. Also, it is highly desirable to reduce noise during take-off and landing. This presents us with a special problem of having to simultaneously deal with a wide range of Mach numbers. On one hand, the acoustic signature of the vehicle is influenced by high-velocity flow entering the intake of the propulsion system. On the other hand, the acoustic effects related to boundary layer ingestion as well as scattering at the intake need to be further investigated and taken into account in a simulation. However, enclosing the entire UAV geometry for performing the wave propagation in 3D is computationally expensive and at the moment, limited to research validation only. Thus, a fast CAA technique that accounts for sound shielding and satisfies the above criteria has been proposed and put forward to discussion at the DLRK 2020 workshop.