Design of Acoustical Features for a quitter Aero-engine Test Facility

Indoor aero-engine test facilities (AETF) are generally used to evaluate the performance of both the newly manufactured and repaired/overhauled engines. Aero Engine Research & Design Center (AERDC) has already commissioned several facilities for testing of turbofan engines of around 40 kN thrust class which powers fighter aircrafts. A request has been received from a customer for installation and commissioning of a new test facility for testing of a similar class engine, with a challenge to make it acoustically better than the existing test facilities. The target was set to reduce the sound pressure level (SPL) in the control room and around the test facility as compared to the existing ones. To meet this requirement, a modified layout with a U-type (vertical intake and exhaust) configuration was planned along with specially designed high and low frequency silencers at the intake, exhaust system with an exhaust basket, splitters in the vertical exhaust chamber, and sound absorbing panels and acoustic doors in the test cell. The above acoustic features have been installed and commissioned as per the proposed layout. A precision sound level meter (make: B&K, model: 2270) has been employed to measure the SPLs of existing AETFs (which is used as the base line data) and the proposed facility at their control rooms and around the test facilities in the audible frequency range (20 Hz to 20 kHz). The maximum measured A-weighted overall SPL in the control room is around 70 dBA, while the engine under test in the test cell generates a SPL of about 140 dBA. Moreover, the SPL at 75-meter radius around the AETF is less than 70 dBA, which makes it one of the quietest AETF available in the country.