Design of acoustic fan tester for fan noise measurement at system resistances

Abstract

Acoustic fan tester was designed, manufactured, and analyzed in order to measure the performance and noise of a fan at various system resistances. Conventional noise measurement of an automotive cooling fan in a free-field is unsuitable to represent the operational environment in practical automobiles. The actual operating conditions have various system resistances owing to the diverse environments of a vehicle engine room. The performance and aeroacoustic of the fan may change if the system resistance changes. However, the suction fan in the fan tester emits considerably larger noise than the cooling fan itself, which causes significant difficulty in measurement of fan noise at system resistances. Therefore, the KAIST Acoustic Fan Tester is proposed in order to measure the fan noises at system resistances. First, the KAIST anechoic wind tunnel was used. It has a silent suction system with two types of muffler in order to reduce the tonal and broadband noise of the suction fan. Second, a new apparatus was designed to measure the fan performance at system resistances. The measured results were validated with reference data obtained from a conventional apparatus. Third, in order to measure only the fan noise at system resistances, the background noise generated by each component of the designed apparatus was analyzed. In addition, an acoustic correction method was proposed to investigate the reflected and scattered noise by the apparatus, the fan noise measured by Acoustic Fan Tester with no resistance and the fan noise measured at the free field are analyzed, Boundary Element Method (BEM) is used for the acoustic correction. Finally, the fan noise when the inflow is changed due to various structures such as a radiator and a condenser in the upstream direction was investigated. Data reduction of non-dimensional fan performance was also proposed considering the upstream system resistance. It is expected that fan noise measurement in a real environment can be performed using the proposed Acoustic Fan Tester. In further study, as downstream system resistances due to engine blocks are researched, it is anticipated that a more accurate real vehicle environment will be implemented.