On application in aeroacoustic investigations of nozzles produced by additive technology

Abstract

The split-type conical nozzles with replaceable outlet sections with diameters of 30, 40 and 50 mm were designed and produced from metal by standard mechanical treatment. In addition, the replaceable outlet sections with the same diameters were produced by additive technology (fused deposition manufacturing) from ABS plastic. In the acoustic anechoic chamber the noise measurements of a single-stream cold air jet for all the nozzles at jet velocities in the range of 0.3-0.7 Mach numbers were carried out. The noise measurements were performed by 6 microphones arranged along an arc with radius of 2 m from the center of the nozzle exit section. The angle between the microphones varies in increments of 15° from 30 to 105°. Preliminarily for each nozzle at the exit section the jet velocity was measured using a Pitot-Prandtl tube. For different directions of noise radiation and different velocities of the jet the graphs of power spectral density and overall sound pressure level were plotted. Their analysis shows that the jet noise for nozzles with diameter of 40 and 50 mm from metal and ABS plastic differs by no more than 1 dB, which is within the measurement error for these types of experiments. The nozzles with diameter of 30 mm have a higher difference in noise, which can be explained by the more sensitivity of a nozzle with a small diameter to the deviations of geometric parameters when manufactured by additive technology.