Development of an Environmental Noise Prediction Code using a Noise Hemisphere based on Rotorcraft Flight Tests

Recently, demand of UAM has been increasing because of the high versatility. However, there are several technical issues that makes the public acceptance about the UAM operation. One of the major issues is the environmental noise problem. It is expected that many UAM vehicles generate high level of the noise during take-off and landing in urban areas, even it should be quieter than environmental noise regulations. In order to verify the regulation satisfaction, the noise should be quantified. Measurements of the noise in the urban areas would be the most reliable way for the quantification, but it is impossible on the current step as there is no airworthiness certification for any UAM vehicles yet. Alternatively, numerical methods efficient for the noise prediction could be used, those are based on the NPD(Noise Power Density) or NHD(Noise Hemisphere Database). In this research, an environmental noise prediction code using NHD was developed and validated. A noise hemisphere can be generated by using this code with flight test data. The noise measurement data from microphones in a flight test are back-propagated to the noise hemisphere with taking into account physical effects such as the spherical spreading and atmospheric absorption of the noise, and curved path propagation. The noise is predicted in a certain area using this code and the generated noise hemisphere. This code was validated in several flight tests with rotorcrafts, and it was concluded that this code is sufficiently accurate with comparing the numerical results with the measurement data.