On the Numerical Evaluation of Tone Noise Emissions Generated by a Turbine Stage: an In-Depth Comparison Among Different Computational Methods

Within the European research project RECORD (Research on Core Noise Reduction) the tone noise emissions of a high-pressure turbine stage have been numerically evaluated by six different academic and industrial partners. The turbine stage geometry and operating conditions match an HPT test rig located at Politecnico di Milano (Italy). Since the constant demand for quieter and greener propulsion system has led to the development of several numerical aeroacoustic codes, this common benchmark represents an important chance to compare the performance of each approach. In this paper, the tone noise results of three distinct categories of numerical solvers (unsteady RANS, harmonic balance and time-linearized approaches) are compared. For the tone noise simulations, all the partners used non-reflecting boundary conditions at the domain inlet and outlet in order to avoid spurious reflections. Moreover, the acoustic modeshapes in the turbine duct were evaluated with different level of complexity by the various partners and different post-processing techniques were employed to extract the acoustic waves from the unsteady solutions. The result comparisons for the blade passing frequency have shown a good agreement (within 4 dB) among the partners in terms of PWL values. Also the acoustic eigenmodes (radial shapes of the pressure waves) and the eigenvalues (axial wave numbers) agree well among the different simulations. A wide range of acoustic results are presented and discussed in the paper.