A Numerical Analysis on the Aerodynamic Noise of Cross-FLow Fan by Using a 2-D Urans Simulation and Acoustic Analogy

C3 - CFD Validation Studies

The aerodynamic noise of the cross-flow fan (CFF) in an air-conditioner (AC) was investigated by using the computational fluid dynamics (CFD) and acoustic analogy. Two-dimensional unsteady flow field of CFF was obtained by solving the compressible Reynolds-Averaged Navier-Stokes (RANS) equation in order to capture the acoustic wave generated from the CFF. The moving mesh technique was adopted at the arbitrary sliding interface between the region rotating with impeller and rest of the region including all stationary parts of AC such as stabilizer, rear guider, etc. The propagated acoustic pressure from the CFF to a microphone was predicted by using the Ffowcs Williams-Hawkings (FW-H) acoustic analogy equation. In the present study, various operating conditions of the CFF were considered in the range of 877-1130 rpm. The results of CFD simulation showed the typical flow field of the CFF such as eccentric vortex which was observed in the vicinity of the stabilizer. Since the flow rate of the CFF is strongly dependent upon the location of the vortex core, the accurate prediction of the location of eccentric vortex is very important. To validate the present numerical analysis, the numerical results were compared with available experimental data such as the sound pressure level (SPL) spectrum and overall SPL. The tonal noise level at the blade passing frequency (BPF) was well predicted in the present study. On the other hand, the prediction accuracy of broadband noise in high frequency was relatively poor. This is because the broadband noise is generated due to the random flow characteristics like turbulence which RANS cannot consider well. The result of the present study, however, can be used for the optimal design of the AC components to reduce the peak sound pressure level which is associated with the tonal noise at BPF.