Аннотация:This paper aims at quantifying the most acoustically radiating modes of the blade unsteady lift and inflow velocity in the circumferential spectral domain and at localizing hot spot interaction areas over the fan. The proposed method is based on the inversion of the Blake model for tonal noise from subsonic fans. The unsteady lift formulation is first used to reconstruct the circumferential blade loading variations from the tonal noise radiation in free field. Then the unsteady lift is related to the inflow velocity distortions by a compressible blade response function. Discretizing the lift and velocity in the direct model leads to ill-conditioned aeroacoustic transfer matrices. The Tikhonov regularization technique is used to stabilize the inversion. The curvature of the L-curve is used to choose the regularization parameter such that the sources' strength vectors are optimally reconstructed. The singular value decomposition and the discrete Picard condition are also used to analyze the stability of the sources' reconstructions. One experimental case is considered to demonstrate the capability of the inverse model to qualitatively reconstruct the blade loading and inflow velocity variations from acoustic pressure measurements in the case of an automotive engine cooling fan.
