ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction: Part II—Influence of the Acoustic Models

Abstract

A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic solvers are compared. Some of the methods resort to the acoustic analogy, while some use a direct approach bypassing the calculation of a source term. Due to differing application objectives, the studied methods vary in terms of complexity to represent the turbulence, to calculate the acoustic response of the stator and to model the boundary and flow conditions for the generation and propagation of the acoustic waves. This diversity of approaches constitutes the unique quality of this work. The overall agreement of the predicted sound power spectra is satisfactory. While the comparison between the models show significant deviations at low frequency, the power levels vary within an interval of ±3 dB at mid and high frequencies. The trends predicted by increasing the rotor speed are similar for almost all models. However, most predicted levels are some decibels lower than the experimental results. This comparison is not completely fair—particularly at low frequency—because of the presence of noise sources in the experimental results, which were not considered in the simulations.

Influence of Swept Blades on Low-Order Acoustic Prediction for Axial Fans

“…This is consistent with the results reported by Sanjose and Moreau on the H380EC1 fan [12]. A negligible shift in frequency is encountered when employing the von Kármán's or Liepmann's models for the LE noise prediction, also in agreement with [12,49]. Several combinations of Butterworth-filter orders have been tested in Figure 13b, appearing to have a negligible effect on the TE noise prediction, with a relative difference of less than 1 dB.…”

Turbine Broadband Noise Predictions Using Linearised Frequency Domain Navier-Stokes Solvers

“…For these configurations, there is an extended agreement that the airfoil geometry impact on broadband noise is small, up to the highest frequencies of interest [4,6,23], since the airfoils are thin and feature a low camber. Recently, the present methodology has been applied to a modern Fan, concluding that the effect of the OGV detailed geometry on sound generation is, in general, small [12,13]. This section compares the results obtained accounting for the airfoil geometry with those obtained by replacing it with a flat plate cascade.…”

“…The solver runs on commodity GPUs [11], enabling the computation of the broadband noise spectra within an industrial design loop. The method has been validated previously for Fan/OGV interaction against experimental data and in a numerical benchmark in the context of the TurboNoiseBB EU project [12,13].…”

Comparison of predicted fan broadband noise using a two- versus a three-dimensional synthetic turbulence method

“…In this work, hot-wire data in the fan interstage as well as acoustic measurement data up-and downstream of the fan stage are used. A more comprehensive overview of the measurement campaign was provided by Guérin et al [34,35] and Kissner et al [36]. For more details regarding the hot-wire measurements, refer to Meyer et al [37].…”