Modeling of aerodynamic noise of quadrotor type aerotaxi

The subject of this work is a study of the current state of modeling the flow around the blades of quadcopters, models of aerodynamic sound generation, formulation, and numerical solution of the problem of generation of rotation noise by the blades of a quadrotor type aerotaxi. The models describing the flow field around the quadrotor blades include the model of nonlinear vortices in lattices, the Reynolds-averaged Navier-Stokes equation (RANS, URANS), the large eddy simulation method (LES), and the direct numerical simulation (DNS) of the system of aerodynamic equations. This paper analyzes the main noise models of different types of aerodynamic origin.  Gutin’s model  is used to describe the noise of the quadrotor rotation, and the Ffowcs -Williams-Hawkings equation  in the formulation of Farassat is used to model the noise taking into account various sound sources. However, these approaches have certain drawbacks that limit their application. The following paper uses a modern approach to modeling noise of aerodynamic origin based on the three-dimensional unsteady equation of sound propagation from a thin blade in the potential approximation, previously proposed by one of the authors of the work. Using this approach, a numerical calculation of the problem of sound generation (rotational noise) of the aerodynamic origin of a quadrotor type aerotaxi was performed. The purpose of the study. Despite the approaches described above, there is a problem associated with achieving an acceptable noise level, i.e. its further reduction. To solve this problem, there is a need to use more accurate models that will allow research on reducing air taxi noise. Tasks of the study. In this regard, the task of modeling noise of aerodynamic origin was set and solved using a refined model of the sound generated by the interaction of the flow and air taxi blades. Research methods are based on the construction and use of a mathematical model for the generation of rotation sound generated by the joint operation of aerotaxi rotors. On this basis, the calculations of the near and far sound fields were performed. A new model for calculating the long-range sound field of a quadrotor type aerotaxi is proposed, which considers the mutual formation of the resulting sound field from the joint operation of 4 propellers. The pressure coefficient and the sound pressure level in the distant sound field were calculated, and the frequency filling of the spectrum of the generated sound wave was investigated. Results and Conclusions. Numerical calculations of the problem of aerotaxi rotation noise generation showed that the maximum pressure level in the generated waves is in the immediate vicinity of the location of the quadrotor screws. However, the maximum value of the pressure level depends on the parameters of the problem, which vary: the thickness of the blade and the speed of the horizontal flight of the aerotaxi. As one moves away from the screws, the local maxima disappear and the wave takes the form of a flat wave. The general level of generated sound (rotational noise) is in the range of 70dB-102dB, which coincides with the results of studies of quadrotor aerotaxi, as well as taxis with the arrangement of propellers according to the aircraft type. The generated rotational noise energy is concentrated in the first 4-5 harmonics. Therefore, the noise model of aerodynamic origin proposed in this study can be used to study the rotation noise of a quadrotor type aerotaxi.