Bastien Caruelle

LAGOON: further analysis of aerodynamic experiments and early aeroacoustics results

This paper presents early results of an experimental aeroacoustic program recently performed in ONERA’s open-jet anechoic windtunnel CEPRA19 with a generic landing gear configuration. This program is the continuation of steady/unsteady flow measurements achieved in 2007 in ONERA’s F2 aerodynamic windtunnel (closed test section). Both experiments constitute the experimental phase of the LAGOON program (LA nding Gear NOise database for CAA validatiON ), currently supported by Airbus and involving ONERA and DLR (the French and German national aerospace research centres) and Southampton University, with the general purpose of evaluate up-to-date CFD/CAA techniques for airframe noise simulation, validated against an extensive experimental aerodynamic/acoustic database. The first point addressed in the present paper is the flow identification between both facilities, relying on limited aerodynamic measurements performed with a 5-hole probe and with onboard static pressure taps and unsteady pressure transducers. This flow identification was supported by a CFD study of the 3D flows in both windtunnels, performed by DLR. It is shown that there exist tiny differences between both flows. The second addressed point is the “signal-to-noise” ratio, or the ratio of the aerodynamic noise radiated by the model, to the background noise measured in the windtunnel without the model. It is shown that this ratio is globally satisfying, especially since this landing gear model with smooth shape is expected to be more silent than an actual landing gear with the same scale.

Computational strategy for predicting CROR noise at low-speed Part I: review of the numerical methods

This paper is the first part of a series of three papers dedicated to the prediction of lowspeed interaction noise of an isolated contra-rotating open rotor (CROR). The objective of this study is to assess available analytical and numerical methodologies in terms of robustness, performance and accuracy. The analytical procedure follows the classical Sears’ theory, while the numerical procedure follows a two-step approach based on CFD coupled with the analogy of Ffowcs Williams-Hawkings (FWH). Concerning the numerical tools, both chorochronic (single-passage) and Chimera (full-annulus) approaches are considered. The prediction of interaction noise requires fulfilling three modelling steps: the aerodynamic perturbations, the rotor unsteady blade response and the resulting noise radiation. Comparisons with noise measurements are provided. It is shown that the results are highly sensitive to the description of the incoming wake deficit. The chorochronic approach, as a single blade passage is computed, allows the use of much finer meshes than the Chimera approach and requires a lower computational cost. This approach is therefore highly attractive for computing isolated axisymmetric configurations.

Computational strategy for predicting CROR noise at low-speed Part III: investigation of noise radiation with the Ffowcs-Williams Hawkings analogy

This paper is the third part of a series of three papers dedicated to the prediction of lowspeed interaction noise of an isolated contra-rotating open rotor (CROR). The objective is to investigate the Ffowcs Williams-Hawkings (FWH) approach for computing noise radiation. Both solid and permeable FWH formulations are investigated to radiate the unsteady pressure to the far-field. Comparisons with noise measurements are provided. It is shown that permeable FWH formulation yields acoustic predictions in better agreement with experimental data as it includes non-linear propagation phenomena within the permeable domain. However, noise source decomposition is made possible with the solid FWH formulation. It is shown that the hub-vortex interaction noise is not negligible whereas the rear row cropping is efficient at reducing tip-vortex interaction noise. Lastly, a highly refined CFD mesh is specified to investigate all non-linear propagation effects downstream of the rear row.

Summary of the LAGOON Solutions from the Benchmark problems for Airframe Noise Computations-III Workshop

The Benchmark for Airframe Noise Computations (BANC) has been initiated by the BECAN Technical Discussion Group under AIAA. This continuous framework, mainly impulsed by NASA LaRC, aims at evaluating numerical methods for the simulation of unsteady flows and aerodynamic noise radiated by airframe components such as airfoil trailing edges, landing gears and high lift devices. In this context, eight test-cases are proposed, with problem statements relying on extended experimental databases. The 2-wheel LAGOON landing gear is one of them. Originally designed and tested in the homonym project funded by Airbus-France, it has a simplified shape, compatible with a wide range of numerical methods, although involving complex physics. This paper summarizes seven submissions that were presented in this category at the Third BANC Workshop in Atlanta in June 2014. Researchers employed various block-structured, unstructured and embedded Cartesian (“octree”) grids and large computational resources to simulate the flow and radiated noise. The solutions are compared against each other and with experimental data gathered in two Onera’s windtunnels, F2 for aerodynamic data and CEPRA19 for acoustic data. Overall, all simulations captured the main features of the unsteady flow and radiated noise, including cavity resonances occurring between the wheels. The acoustic spectra and directivity diagrams of overall sound pressure levels are in fair agreement with experiment, although a significant dispersion can be observed between all contributions.

Aeroacoustic Simulation of Double Diaphragm Orifices in an Aircraft Climate Control System

Transient CFD acoustic source prediction and CA propagation studies of a double diaphragm orifice illustrate complex flow and aeroacoustics phenomena, combining shedding structures (tonal noise) and large eddy structures (broadband noise). Such studies are necessary for aircraft climate control systems because such components introduce nonlinearities in the system characterization. In this paper we investigate, through modeling, the noise signature of a given double diaphragm configuration comparing against microphone measurements the predicted noise spectra in the near field (source region) and the predicted propagated sound in the far field, some distance downstream of the source region. A second configuration is then assessed, with the spacing between the orifices doubled, so as to derive confidence that the modeling is accurate in both absolute and differential terms. A novel method is presented for estimating the mesh frequency cut-off from a steady-state CFD calculation; such an estimate gives valuable insight a priori into the local mesh refinement required for a transient CFD calculation to resolve the frequency range of interest. The work described in this paper is part of a wider evaluation into the use of CAA methods for aircraft climate control systems.

Handling of Non-Periodic Contra Rotating Open Rotor Data

In this contribution, we present two different concepts to handle the non-periodic nature of Contra Rotating Open Rotor (CROR) if the front and the aft rotor rotate with a slightly different rotational speed. The first procedure that is presented consists of a correction matrix applied to the source data used in the DLR FWH-code APSIM+. For periodic data the correction matrix reduces to the identity matrix, thereby recovering the standard Fourier transformation. The second method is based on the Vanicek approximation, and consists of a successive least-square approximation of non-periodic data. The developed methods are tested with artificially generated data, illustrating the ability to accurately representing non-periodic data. A comparison between the two methods shows that the first method is more accurate than the Vanicek approximation. Preliminary results on actual non-periodic CROR data reveals the influence of the non-periodic correction as compared to uncorrected data, i.e., differences ranging up to 10 dB are seen for the considered cases.

Prediction of Contra-Rotating Open Rotor broadband noise in isolated and installed configurations

Broadband noise is a significant part of the noise emitted by contra-rotating open rotors. Several noise sources can contribute to the total broadband sound field, with the most dominant ones probably being trailing edge noise, rotor-wake interaction noise and pylon-wake interaction noise. This paper addresses the prediction of these noise sources using analytical models based on Amiet’s flat plate airfoil theory and also to empirical turbulence models, fed by input data extracted from steady and unsteady CFD RANS simulations. The models are assessed against wind tunnel tests of Rolls-Royce’s rig 145 (build 1) conducted at the DNW anechoic open jet test facility using Rolls-Royce blades and Airbus pylons. The study showed promising results in terms of the ability of the models to predict acoustic power spectrum shapes, peak frequencies and absolute levels. The effects of changes in thrust on broadband wake-interaction noise are well reproduced. However, the models significantly underestimate the effect of thrust on trailing edge noise and the effect of rotational velocity on pylon interaction noise.

Computational AeroAcoustics of a Realistic Co-Axial Engine in Subsonic and Supersonic Take-Off Conditions

The present work is devoted to the numerical simulation of acoustic emissions characterizing turbojet engines, a subject that is relevant of the more general purpose of aircraft noise prevision and reduction. More precis ely, we explore here the ability of a structured CAA (Computational AeroAcoustics) method/solver to address complicated problems of engine noise prediction. With that end, and by using the ONERA’s CAA solver sAbrinA.v0 , we conduct realistic calculations of aft fan nois e emission, which involve both a full-3D exhaust geometry (with its pylon / internal bifurcations) and typical fan noise modal contents (high azimuthal order / frequency). The re sults highlight how far the installation / refraction effects induced by the complex geometry / flow of an engine can affect its fan noise emission. Results also tend to demonstrate that bot h the here used CAA method and solver are mature enough to face out industrial-like engin e noise problems.

Jet noise prediction using RANS CFD input

In the present work, a volume source model based on the SNGR approach, first proposed by Bailly, has been implemented and developed for jet noise prediction purposes. This method presenting the advantage of providing unsteady three‐dimensional turbulent data from a RANS computation, it shall be compatible with industrial development processes. First, the theoretical aspects of the original SNGR model were revisited. More particularly, analytical developments showed that considerable modifications were needed to take local flow effects into account while generating unsteady turbulent data. Moreover, the way to include anisotropy effects in the model, as originally proposed by Billson, was improved by using a nonlinear extension of Boussinesq approximation to recover the local Reynolds stress tensor. In a second step, the potentialities of the stochastic tool for jet noise simulations have been evaluated against existing numerical and experimental databases. In addition to that concern, its sensitivity to a...

Simulation of a Generic Two-Wheel Nose Landing Gear Using High-order Finite Difference Schemes

Aerodynamic noise from a generic two-wheel landing gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow field is computed by using a compressible Navier-Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface data is used in a FW-H solver to predict the far field noise levels. Both aerodynamic and aeroacoustic results are compared with wind tunnel measurements and are found in good agreement. Individual contributions from three components, i.e. wheels, axle and strut of the landing gear model are also investigated to identify the major noise source component. It is found that wheels are the dominant noise source in general. Strong vortex shedding from the axle is the second major contributor to landing gear noise. This work is part of Airbus LAGOON (landing gear noise database for CAA validation) program with the general purpose of evaluating up-to-date CFD/CAA and experimental techniques for airframe noise prediction (see AIAA Paper 2008-2816 by Manoha, Bulte and Caruelle, and AIAA Paper 2009-3277 by Manoha, Bulte, Ciobaca and Caruelle).