Microphone-Array Measurements in a Cryogenic Wind Tunnel

Based on previous studies with microphones and electronic equipment in a cryogenic environment, a test array for cryogenic application has been developed. Electret microphones, electronic equipment, and fairing material have been successfully tested by the authors under cryogenic conditions and have demonstrated long-term stability. Subsequently, acoustic array measurements performed in a cryogenic wind tunnel for various temperatures in the range of 100 to 300 K, using a single-rod configuration, are described in this paper. The Mach number was in the range 0.1 to 0.3, and the Reynolds number (based on the cylinder diameter of 2.5 mm) was in the range of 5 . 10(3) to 8 . 10(4). The experiments demonstrated the technical feasibility of performing aeroacoustic array measurements at these low temperatures. A systematic study of Reynolds- and Mach-number effects on the radiated noise of a single-rod configuration has been conducted. The results showed good agreement between theory and measured sound radiation. A Reynolds number dependency of the measured and predicted sound power can be shown.