Validation of a 3D Linearized Method for Turbomachinery Tone Noise Analysis

A fully three-dimensional noise propagation analysis method accounting for 3D radial modes was developed in order to predict the tone noise emissions of a multistage low-pressure turbine. This propagation procedure employs a time-linearized aeroacoustic solver with 3D non-reflecting boundary conditions to compute the acoustic response of each single row and allows the acoustic waves to propagate across adjacent rows up to the turbine exit, where such perturbations radiate to the far field. This method follows the evolution of the acoustic modes within the machine, taking into account both circumferential and radial mode orders. The overall turbine exit sound power level, due to specific rotor-stator interactions, may thus be evaluated. Some numerical results are compared with experimental data measured in an acoustic two-stage test rig which is representative of the last stages of a low-pressure turbine in terms of row geometry, blade loading and flow deflection.