Study on the Accuracy of the Kirchhoff Approximation-based Integral in Acoustic Scattering Simulation

Acoustic scattering has been a common problem in aeroacoustics. It can be solved numerically using the Kirchhoff approximation-based integral, which shows great advantages in accuracy and efficiency at high frequency. The purpose of this paper is to investigate the accuracy of this method for varied Helmholtz number ka and grazing angle φ., focusing on the lower-limit of ka and the upper-limit of φ. The numerical method was firstly validated through two well-known benchmarks, and then applied to cases with different grazing angles. To verify the accuracy of the numerical results, relevant experiments were conducted. In this paper, a ‘loudspeaker-pipe’ device was used as a monopole source generator and its directivity has been verified. The scattering experiments of spherical waves by a panel at grazing angles of 0°, 25° and 40° were conducted respectively, of which the results show that the method can provide accurate predictions for ka≥1.5890, φ ≤25° at least. Error analysis was also given for results with bad agreement.