Design and Qualification of an Anechoic Facility in PNRPU

The paper describes the anechoic facility built in Perm National Research Polytechnic University (PNRPU) in 2014-2015 with the objective of studying noise of turbulent jets, vortex rings, and airframe noise. At present, the only other analogous facility in Russia is anechoic chamber AC-2 of TsAGI built in 1970s. One of the most important characteristics of an anechoic facility is a region where inverse square law spreading holds within some tolerance, i.e. where the free-field conditions are observed. Acoustic qualification is aimed at determination of this region in the facility. The present paper provides the results of acoustic qualification of the anechoic chamber in PNRPU, which show that the free-field conditions in the facility are realized within 3 m radius from the sound source for broadband noise in the frequency range 125 Hz - 20 kHz. Therefore, the study demonstrates that the anechoic facility in PNRPU allows aeroacoustic experiments to be performed for obtaining quantitative results. The present work restores domestic competences in design of aeroacoustic experimental facilities, which is important in view of the plans to build in Russia an anechoic wind tunnel with hot flow AKT TsAGI for large-scale aeroacoustic tests.