Revealing the acoustic rotational Doppler effect from rotating objects without incoming waves
Phys. Rev. Applied 25, 014023 – Published 9 January, 2026
DOI: https://doi.org/10.1103/tbqs-3vkp
Abstract
The rotational Doppler effect (RDE), pivotal in metrology and communication, has been exclusively observed through angular momentum transfer from incoming waves to rotating objects, limiting its compactness and practicality. Here we demonstrate an RDE phenomenon originating directly from rotating objects without incoming waves. We show that the steady loading on a rotor inherently generates spinning acoustic vortex (AV) modes, which share the object’s angular velocity and carry orbital angular momentum. These spinning AV modes produce different rotational Doppler shifts, and the resulting acoustic energy is correlated with AV phase stability. Furthermore, we reveal that rotor tonal noise arises from the constructive interference of AV modes with identical topological charges generated by each blade. Our work builds a bridge between rotor tonal noise in aeroacoustics and AVs carrying orbital angular momentum in classical acoustics via the disclosed RDE from rotating objects. On one hand, we leverage steady blade loading to compactly generate tunable AV modes. On the other hand, we exploit AV characteristics to achieve highly robust noncontact detection of rotating objects and further reveal the phase synchronization mechanism for tonal noise reduction. Our findings have the potential to stimulate further research and may pave the way for new applications based on the RDE.
