Abstract

The flow-induced noise generated from the rotor in the operation of air taxis will be one of the issues that we will face. In this paper, the flow noise generated by rotors on the shape of the air taxi designed conceptually was numerically analyzed as the first step to reduce the flow noise of air taxis. The commercial code, Cradle CFD, was introduced to solve the three-dimensional Reynolds-Averaged Navier-Stokes analysis in the steady-state analysis and the LES model in the unsteady-state analysis, respectively. Also, the commercial code, Actran, was used to predict the flow-induced noise. To predict the flow-induced noise of the UAM, we need unsteady CFD results. The CFD analysis has been conducted by the following process: Step 1. steady-state analysis, Step 2. the first unsteady-state analysis, and Step 3. the second unsteady-state analysis. The steady-state analysis was performed to obtain roughly and quickly the flow field in the computational domain, and then the first unsteady-state analysis was carried out to enough develop the unsteadiness in the flow field during three rotations of the rotors. After the first unsteady-state analysis, the second unsteady-state analysis during four rotations of the rotors was performed to obtain the flow field data required for analyzing the flow-induced noise. The flow-induced noise was predicted through the terms of dipole and quadrupole in the FW-H(Ffowcs Williams and Hawkings) equation using the wall pressure fluctuations about the time obtained in the flow field of the second unsteady-state analysis as an input value. Through the flow-induced noise analysis, the mechanism generating the noise was found, and the noise sources were identified differently according to the installation position of each rotor on the air taxi. For the development of low noise air taxis, it is necessary to reduce the noise generated by the main rotor as well as to consider the noise source depending on the location of each rotor.