Optical Measurement Technique for Supersonic Jet Noise Using Laser and Position-Sensitive Detector

Precise near-field measurement of supersonic jet noise is essential for understanding its generation mechanisms and for developing effective noise mitigation strategies. However, conventional microphones often interfere with both the acoustic field and the flow field due to their physical presence. To address this limitation, this study proposes a novel non-intrusive measurement technique that utilizes a laser beam and a position-sensitive detector (PSD) to simultaneously capture the sound pressure and direction of supersonic jet noise. The underlying principle involves detecting deflections in the laser beam induced by acoustic density fluctuations in the acoustic field. This paper presents the experimental setup and signal processing methodology used to extract sound pressure level (SPL) and direction-of-arrival (DOA) information from the PSD output signal. Validation experiments demonstrate excellent agreement between the proposed technique and conventional methods such as free-field microphones and sound intensity probes, confirming the technique’s potential for aeroacoustic diagnostics in challenging or inaccessible environments.