Validation of 3D Acoustic Propagation Code with Analytical and Experimental Results

Abstract

Acoustic propagation in a turbofan engine inlet nacelle often can not be accurately described with a two-dimensional (2D)/axisymmetric model due to nacelle droop and circumferentially non-uniform acoustic liners. This paper describes the development and validation of a three-dimensional (3D) frequency domain linearized Euler equations (LEE) solver. The method accounts for complex nacelle geometry, non-uniform mean flow, and non-uniform acoustic liners. In order to test the 3D propagation, a simple case involving a spinning mode in a circular duct with and without flow is modeled and compared with analytical results. In order to validate simulations involving acoustic liners, the NASA Langley Flow Impedance Tube facility is modeled for several flow conditions and liner impedances and compared with experimental data. Simulations are also performed for a single mode propagating in a JT15D turbofan engine inlet in a static test configuration in order to test propagation in non-uniform mean flow and non-simple geometry. The numerical results agree very well with the analytical and experimental data. Finally, the code is applied in the study of scattering from acoustic liner splices. Simulations are performed for a spinning mode in a circular duct with a liner possessing two hardwall splices. These results are compared with available numerical results.