Prediction of small-scale UAS rotor noise

Abstract

A model framework used to assess the noise generated by small-scale rotors, such as those found on small Uninhabited Aerial Systems (sUAS), is presented. The model is based on analytical and semi-empirical models, with input from full 3D Computational Fluid Dynamics (CFD) steady -state Reynolds-Averaged Navier-Stokes solutions. The acoustic signature of a commercially available 2-blade rotor in hover is considered, namely the DJI-CF 9.4×4.3 which has a diameter 0.24 m. The operating conditions are matched to experimental data for a rotor in quiescent air and with a rotation speed of 5400 rpm. At 75% radius, this gives a flow M ach number of 0.15 and Reynolds number, based on local chord, of 51,400. The CFD simulations were conducted in a multiple reference frame (M RF) model within the Ansys Fluent 19.3 solver. Boundary layer properties were extracted from this flow field at 2D chordwise slices along the blade span, and used as inputs to the semiempirical model. The predicted noise of both narrowband and broadband are compared with published experimental measurements, and the agreement is found to be reasonable.

Numerical and experimental investigation of propeller noise with trailing-edge serrations

“…The latter consists of mainly the trailing-edge noise, which is generated via the scattering of a turbulent boundary layer by the sharp trailing edge [3]. Chen et al [4] developed a semi-empirical noise prediction framework for small-scale rotors and concluded that trailing-edge noise is the primary component of the broadband noise for the rotors [4]. At a much larger scale, Oerlemans et al [5] also found that the trailing-edge noise is the dominant broadband noise source for a utility-scale wind turbines.…”