Measurement of radiated sound directivity of moving sources at low Mach numbers

It is well known that frequency and amplitude modulation occur when sound sources move. However, there are few studies on the effect of the sound source movement on its directivity. We performed an experiment using a scaled train model moving at low Mach number between 110 and 290 km/h, with an ultrasound speaker. We then estimated the directivities of radiated sound from the source by measurements using a stationary microphone. We also calculated simulated directivities theoretically as a combination of source term and motion term. Thus, we compared the measured and simulated directivities. As a result, it was confirmed that the two kinds of directivities were in good agreement.