Identification of Noise Sources in a Realistic Turbofan Rotor Using Large Eddy Simulation

Kholodov, Pavel; Moreau, Stéphane

doi:10.3390/acoustics2030037

Cited by 22 publications

(9 citation statements)

References 27 publications

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“…The TLV can be identified by the low streamwise velocity and is characterized by large levels of turbulent kinetic energy. Unlike previous studies on the tip leakage flow in a fan stage at approach condition [34][35][36], the TLV appears relatively close to the trailing edge, which may be related to the blade tip geometry and the tip clearance, which is larger than 1% of the chord length and increases towards the trailing edge. Furthermore, the blade airfoil at the tip presents a significant change in the slope between the leading edge and the maximum camber position, the airfoil is relatively flat and thin, and the position of the maximum camber is located at 70% of the chord length.…”

Section: Aerodynamic Resultscontrasting

confidence: 75%

Direct noise predictions of fan broadband noise using LES and analytical models

Al-Am

Clair

Giauque

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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In the present study, we analyze the broadband noise of an ultra high by-pass ratio fan/OGV stage developed at Ecole Centrale de Lyon. Wall-modeled large eddy simulations (LES) of a periodic fan/OGV sector are performed at approach conditions on an unstructured grid that is well refined for direct noise propagation. Comparisons between wall-resolved and wallmodeled computations are performed using a 2.5D simplified configuration of the fan/OGV stage, and show a good agreement. This justifies the use of wall-modeled simulations for the full-span configuration. A good agreement is found between LES and RANS aerodynamic results. However, some differences can be found in the tip gap region and near the hub, where large coherent structures appear. Additionally, a small recirculation bubble can be observed from approximately 60% of the fan blade span in the LES. In this study, the broadband noise is directly computed from the fully-compressible LES solver and compared with predictions from available analytical models. The input data for the analytical models, such as mean and turbulent flow statistics, are obtained from the LES computation. A good agreement is found for the predicted sound power levels between direct LES noise predictions and the LES-informed analytical models. This confirms the capability of the LES numerical setup to directly predict far-field noise. However, some discrepancies can be observed at low frequencies. These might be attributed to the additional noise sources that are present in the LES, which are not considered by the analytical models.

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Section: Aerodynamic Resultscontrasting

confidence: 75%

Direct noise predictions of fan broadband noise using LES and analytical models

Al-Am

Clair

Giauque

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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“…Only few CFD studies have performed high-fidelity simulations to solve the fan/OGV system and analyse the fan broadband noise [9][10][11][12][13][14][15]. Table . 1 shows the computational configuration and cost in these simulations.…”

Section: Les/lbm With Acoustic Analogymentioning

confidence: 99%

“…Comparing Casalino et al [14] and Arroyo et al [12], it is clear that the LBM-based method is much more time efficient, although the CPU performance in the two studies are different. [13] LES (fan only)…”

Section: Les/lbm With Acoustic Analogymentioning

confidence: 99%

“…In this section we outline how the target velocity cross-spectrum used to validate the synthetic turbulence method may be estimated from the RANS solutions of the flow field over the OGV leading edge plane. However, we emphasise that more accurate cross-spectrum are generally required for accurate fan broadband noise calculations obtained from either from Hot-wire measurements or high fidelity time-resolved CFD such as LES [9][10][11][12][13] or LBM [14,32].…”

Section: Modelling Of Velocity Cross-spectra Of Rotor Wakementioning

confidence: 99%

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Proper Orthogonal Decomposition Method for the Prediction of Fan Broadband Interaction Noise

2022

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The turbulent wakes generated by a rotor interacting with outlet guide vanes (OGVs) is one of the dominant broadband noise sources in a turbofan engine. An accurate representation of the rotor wake turbulence is therefore important for the reliable prediction of the rotor-OGV interaction noise. This paper presents a turbulence synthesis method based on a spectral Proper Orthogonal Decomposition (POD) representation of the turbulent wake that aims to reproduce the desired velocity cross-spectrum along the OGV leading edges where noise is emitted due to turbulence-OGVs interaction. The method is first developed in the frequency domain based on a superposition of vortical modes with the appropriate amplitudes. Fourier modes and POD modes are proposed to represent the two-point velocity spectrum. The POD modes will be shown to be highly efficient in reconstructing the flow field near the tip region where a largescale coherent structure is present. An extension of the POD synthetic turbulence method to the time domain is also presented by means of a white noise filtering technique to allow the generation of time varying velocity signals with the desired cross spectral characteristics. The results show that both the one-and two-point statistics can be closely reproduced. The proposed frequency-domain POD synthetic turbulence method for fan broadband noise prediction for a realistic fan-OGV configuration is illustrated by the use of a frequency-domain linearised Navier-Stokes solver to predict the sound power radiation due to each vortical mode. Overall sound power levels at a number of discrete frequencies are predicted and compared against measured noise data. Agreement is found to be within the uncertainty of the noise sound power measurement.

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“…The objective of this study is to identify the most suitable technique for the estimation of turbulence parameters, namely, the turbulence integral length scale and the turbulence intensity (which can be understood as a normalized turbulent kinetic energy (TKE)). Commonly, methods for fan broadband noise prediction are based on analytic models [14][15][16][17], synthetic turbulence methods [18,19], and scale-resolving techniques [6,20,21]. They depend on turbulence parameters, which can include boundary layer thickness, turbulence integral length scale, and flow turbulence kinetic energy of the inlet flow or/and of the flow at the fan interstage section.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Techniques for the Estimation of Flow Parameters of Fan Inflow Turbulence from Noisy Hot-Wire Data

Caldas

Kissner

Behn

et al. 2021

Fluids

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Turbulence parameters, in particular integral length scale (ILS) and turbulence intensity (Tu), are key input parameters for various applications in aerodynamics and aeroacoustics. The estimation of these parameters is typically performed using data obtained via hot-wire measurements. On the one hand, hot-wire measurements are affected by external disturbances resulting in increased measurement noise. On the other hand, commonly applied turbulence parameter estimators lack in robustness. If not addressed correctly, both issues may impede the accuracy of the turbulence parameter estimation. In this article, a procedure consisting of several signal processing steps is presented to filter non-turbulence related disturbances from the unsteady velocity data. The signal processing techniques comprise time- and frequency-domain approaches. For the turbulence parameter estimation, two different models of the turbulence spectra—the von Kármán model and the Bullen model—are fitted to match the spectrum of the measured data. The results of several parameter estimation techniques are compared. Computational Fluid Dynamics (CFD) data are used to validate the estimation techniques and also to assess the influence of the variation in window size on the estimated parameters. Additionally, hot-wire data from a high-speed fan rig are analyzed. ILS and Tu are assessed at several radial positions for two fan speeds. It is found that most techniques yield similar values for ILS and Tu. The comparison of the fitted spectra with the spectra of the measured data shows a good agreement in most cases provided that a sufficiently fine frequency resolution is applied. The ratio of ILS and Tu of the velocity components in longitudinal and transverse direction allows the assessment of flow-isotropy. Results indicate that the turbulence is anisotropic for the investigated flow fields.

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Identification of Noise Sources in a Realistic Turbofan Rotor Using Large Eddy Simulation

Cited by 22 publications

References 27 publications

Direct noise predictions of fan broadband noise using LES and analytical models

Direct noise predictions of fan broadband noise using LES and analytical models

Proper Orthogonal Decomposition Method for the Prediction of Fan Broadband Interaction Noise

Comparison of Techniques for the Estimation of Flow Parameters of Fan Inflow Turbulence from Noisy Hot-Wire Data

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