Jerome de Laborderie

Compressor Stage Broadband Noise Prediction using a Large-Eddy Simulation and Comparisons with a Cascade Response Model

The present work addresses the rotor-stator interaction broadband noise prediction. The objectives are first to develop a numerical acoustic method and second to deepen the understanding of this noise mechanism to improve an existing analytical model. The two steps of the numerical method consist in performing a Large-Eddy Simulation of an actual rotor-stator stage in order to directly extract the broadband pressure fluctuations on the stator vanes. Then the latter are used as equivalent noise sources in Goldstein acoustic analogy in the frequency domain. An axial flow compressor stage is used as a test case. The mean and unsteady components of the flow are analyzed. The turbulent properties of the flow needed in the analytical model are extracted from the LES. The unsteady pressure on the vanes predicted by the LES exhibits very different behaviors depending on the position on the vane that are attributed to several mechanisms such as turbulent wake interaction or boundary layer transition. The spanwise coherence length representing a crucial parameter for the analytical model is also investigated from the numerical vane response, showing a longer value than the one usually considered in the analytical model. The acoustic power spectra predicted by both approaches are compared and the effect of the spanwise coherence length is studied.

Several technological effects on tonal fan noise prediction

This work aims at evaluating some technological effects usually not included in analytical or semi-analytical tonal fan noise prediction models. The methodology consists in comparing unsteady Computational Fluid Dynamics data, taking successively into account some realistic effects, with the results from a cascade response based model for rotor/stator interaction. The simulations are performed with the turbomachinery flow solver Turb’Flow on a simplified stator vane cascade. They allow evaluating and discussing the effects of both model hypotheses of no vane thickness and inviscid flow on the acoustic sources predictions. The effects of these assumptions are then assessed in terms of modal acoustic powers radiated within the duct. A similar study is performed on a realistic low pressure compressor stage. The effects of the stator vane geometry as well as the real flow configuration on the acoustic sources, extracted during the unsteady simulation, are quantified relatively to the analytical prediction of the vane loading. Finally a comparison of the acoustic powers given by both methods results in an estimation of the technological effects on the propagated noise.

Camber effects in cascade-gust interaction noise through a simple extension of analytical models

This paper introduces a two-stagger angles method to take into account some effects of camber in cascade-gust interaction noise through a simple extension of a flat-plate based analytical model. The emphasis is put here on cascade-gust interaction tonal noise, for which camber effects are known to be significant, but the present method can be similarly used for broadband noise predictions. Numerical results from a 2D and a 3D test-cases are compared with analytical predictions with and without camber effects, and a clear improvement of the agreement is observed when the method for camber effects is used.

Evaluation of a Cascade-Based Acoustic Model for Fan Tonal Noise Prediction

This study aims at evaluating an analytical model for the prediction of tonal fan noise created by the rotor–stator interaction. The methodology consists of comparing unsteady flow simulations with the cascade-based acoustic model to quantify the influence of some technological effects not included in the model. The simulations are performed with a dedicated turbomachinery flow solver Turb’Flow on a simplified stator vane cascade. They allow discussing the effects of both model assumptions of no vane thickness and inviscid flow on the predictions of the acoustic sources as well as on the modal acoustic powers radiated within the duct. The Kutta condition is found to be efficient to locally represent the viscosity effects, and the vane thickness tends to moderately modify the distributions of the sources and the amplitudes of the duct modes. Moreover, a three-dimensional decomposition of the aerodynamic excitation is proposed and coupled with the three-dimensional analytical cascade response. This fully th...

Prediction of Noise Sources in Axial Compressor from URANS Simulation

As part of a larger aeroacoustic study focused on rotor–stator interaction noise, the unsteady flow in a single-stage axial compressor is achieved by a numerical Reynolds-averaged Navier–Stokes simulation. The flowfield is precisely analyzed and assessed by comparing it with available experimental and numerical data. Specifically, the rotor wakes correctly agree with previous laser Doppler anemometry measurements. The unsteady flow, especially the potential effects created by the stator vanes, is then investigated, showing that the stator potential field is responsible for a major secondary tonal noise source on the rotor blades. The rotor wake velocity and turbulent content correspond to the excitations for tonal and broadband noise, respectively. They are greatly influenced by the vane potential effects and, to a lesser extent, by their convection with the mean flow. Two methods of extraction are surveyed along the whole span, showing the need to consider the blockage induced by the stator on the wakes....

LES of the LS89 cascade: influence of inflow turbulence on the flow predictions

Free-stream turbulence preceding high-pressure turbine blades has a crucial impact on blade fields including the heat transfer on the wall. Many parameters characterize this turbulence; its intensity, length scales and physical spectrum are addressed in the study of various operating points of the LS89 configuration. Usually, operating points where weak turbulence is injected are well predicted for all fields by Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). The MUR235 operating point however, with an experimentally injected turbulence level of 6%, remains incorrectly predicted when im-posing the experimental values in the simulations. Such difficulties raise many questions amongst which mesh size and turbulent kinetic energy spectrum are of specific importance for LES. Going away from synthetic turbulence injection by imposing a physical energy spectrum can help improving the prediction of heat transfer. From the present study, it seems that turbulent spots developing in a pre-transition region for higher levels of tur-bulence on the suction side are important features to capture for proper predictions. In parallel, typical structures of boundary layers such as streamwise oriented vortices have been observed and their existence conditions the heat transfer field on the blade wall. From this specific study, all of these physical processes are seen to be highly dependent on the turbulent specification and turbulent transition observed for the MUR235 case. De-pending on these inflow specifications, a transitional boundary layer may be encountered upstream of the shock thus modifying the heat transfer profile.

Analysis of a high-pressure multistage axial compressor at off-design conditions with coarse Large Eddy Simulations

This paper aims at evaluating Large Eddy Simulations (LES) for the prediction of the performance line and flow at off-design conditions in a multistage high-pressure compres-sor. A coarse and an intermediate grid are specifically investigated, since their associated computational cost appears affordable in an industrial context. Several operating condi-tions of the 3.5 stages high-pressure compressor CREATE are simulated, then results are compared to experimental data and to an existing URANS simulation. Both grids yield iso-speed performance lines close to experimental measurements, but only the intermedi-ate one is able to correctly predict the experimental point at lowest mass flow rate. The unstable regime is specifically investigated in the last stage of the intermediate grid, show-ing the presence of rotating instabilities. Their amount and spinning velocity are similar to experimental observations and previous URANS results. Hence coarse LES appears as an interesting tradeoff for off-design predictions of flow in a multistage compressor.