Time-Domain Harmonic Balance Method for Turbomachinery Aeroelasticity

The present paper investigates a time-domain harmonic balance method as an alternative to classical time-marching schemes for stability studies of turbomachineries toward flutter. A weak-coupling approach is applied, which requires computing the fluid response to prescribed harmonic motions of the structure. The harmonic balance method, formulated in the arbitrary Lagrangian/Eulerian framework, is adapted to single-passage reduction using phase-lag boundary conditions expressed purely in the time domain. Validation against experimental data for the 11th standard configuration for aeroelasticity is performed, showing good agreement. Finally, an industrial test case is presented: a fan designed by Safran Snecma. The results show the good accuracy of the proposed harmonic balance method as well as significant reductions in computational time

Contrasting the Harmonic Balance and Linearized Methods for Oscillating-Flap Simulations

In the framework of unsteady aerodynamics, forced-harmonic-motion simulations can be used to compute unsteady loads. In this context, the present paper assesses two alternatives to the unsteady Reynolds-averaged Navier–Stokes approach, the linearized unsteady Reynolds-averaged Navier–Stokes equations method, and the harmonic balance approach. The test case is a NACA 64A006 airfoil with an oscillating ␣ap mounted at 75% of the chord. Emphasis is put on examining the performances of the methods in terms of accuracy and computational cost over a range of physical conditions. It is found that, for a subsonic ␣ow, the linearized unsteady Reynolds-averaged Navier–Stokes method is the most ef␣cient one. In the transonic regime, the linearized unsteady Reynolds-averaged Navier–Stokes method remains the fastest approach, but with limited accuracy around shocks, whereas a one- harmonic harmonic balance solution is in closer agreement with the unsteady Reynolds-averaged Navier–Stokes solution. In the case of separation in the transonic regime, the linearized unsteady Reynolds-averaged Navier–Stokes method fails to converge, whereas the harmonic balance remains robust and accurate

A Harmonic Balance Method for Aerodynamic Damping Prediction in Turbomachinery

The present paper investigates a time-domain harmonic balance method as an alternative to classical time-marching schemes for the stability study of turbomachineries toward flutter. This study is performed in a weak coupling approach, which requires to compute the fluid response to prescribed harmonic motions of the structure. The harmonic balance method is adapted to single sector reduction and an arbitrary Lagrangian/Eulerian formulation. Two different industrial test cases are presented: an axial compressor used in a Turbomeca helicopter engine and a fan designed by Snecma. The results show the good accuracy of the proposed harmonic balance method as well as significant reductions in computational costs

Analyse de l’impact d’ingestion de vortex sur la réponse dynamique d’un fan à la raisonnance.

International audienceUltra high bypass ratio (UHBR) turbofan configurations are promising concepts to address the issue of aircraft fuel burn reduction. The large fan diameter and the small ground clearance of these configurations can lead to ingestion of ground vortex during takeoff phases. This vortex can be responsible of high level of vibrations and possible failure due to high cycle fatigue. The objective of the work described in this paper is to investigate the forced response due to ground vortex ingestion of a large civil fan in resonance condition. This paper is separated in three sections. The first one consists of characterizing the flow distortion induced by a ground vor-tex. The second part consists of evaluating the blade vibrations induced by this vortex with decoupled aeromechanical method. The numerical predictions are then compared to experimental results. And finally, the last part consists of proposing a low fidelity model based on swirl distortion in order to estimate modal aerodynamic forces in ground vortex ingestion case.Les turbofans à forts taux de dilution sont des configurations prometteuses pour réduire la consommation de carburants des avions. Le grand diamètre du fan et la faible garde au sol de ces configurations peuvent entraîner une ingestion de vortex de sol pendant les phases de décollage. Ce vortex peut être responsable de forts niveaux de vibration et peut conduire à une rupture mécanique due à une fatigue megacycle. L'objectif du travail décrit dans cet article est d'étudier la réponse forcée due à l’ingestion du vortex de sol d’un turboréacteur civil. Cet article est décomposé en trois parties. La première consiste à caractériser la distorsion aérodynamique générée par le vortex de sol. La seconde partie consiste à évaluer le niveau de vibration induit par le vortex de sol à l’aide d’une approche aéromécanique découplée. Les résultats numériques sont comparés aux résultats expérimentaux disponibles. La dernière partie consiste à proposer un model basse fidélité basé sur la cartographie de distorsion d’angle permettant d’estimer les forces aérodynamique modales dans le cas d’une ingestion de vortex

Computing Fluid Structure Interaction Coupling Time Spectral Method (TSM) and Harmonic Balance Method (HBM)

International audienceThis paper deals with fluid-structure interactions (FSI), involving a blade profile, submitted to different sources of excitations, as if it were included in a real engine. Two forces of excitation will be considered on the NACA 64A010 airfoil, described in : an external force, due to a forced rotation motion of the blade, and an aerodynamic force, induced by fluid flow around the structure.By using the Harmonic Balance Method, the airfoil’s motion equation becomes an algebraic problem. Then, this system is solved for each frequency of a chosen range. Therefore, the fluid effect on the translation motion of the profile is studied.To compute the time periodic aerodynamic field, the Time Spectral Method, implemented in the Onera’s elsA solver, is used for a fast and efficient resolution. This method relies on a time-integration scheme that turns the resolution of the turbulent Navier-Stokes problem into the resolution of several coupled steady state problems computed at different instants of the time period of the movement. The Theodorsen approach with several hypothesis exposed in allows an analytic estimation of the unsteady lift effort. The two approaches are compared for an imposed motion.In order to predict the dynamic behavior of the system, a fully coupled numerical methodology is developed. For each frequency and at each iteration, TSM supplies the flow field which is used by HBM as a nonlinear excitation on the structure to computate a periodic response and conversely, HBM supplies the new deformed mesh used by TSM to compute the flow field. This strategy has the advantage that all computations take place in the spectral domain, allowing thus to find the steady-state behavior of the fluid and the structure without computing any transient state. The analysis provides the Frequency Forced Response. Some frequencies in the range corresponding to a contribution change between structure and fluid damping are precisely highlighted

Unsteady transonic wing nacelle interference for different oscillatory modes

Abstract. This paper presents results of the numerical part of the DLR-ONERA project WIONA (Wing with Oscillating Nacelle). Unsteady aerodynamics of a generic wingpylon- nacelle configuration is investigated and CFD simulation tools are validated with test results and against one another. The results show that for the present configuration unsteady aerodynamics for different forced oscillations, of the whole model as well as of pylon and nacelle alone, can be precisely predicted in transonic flow including shock induced separation

Numerical unsteady aerodynamics for turbomachinery aeroelasticity

Communication to : 10th international symposium on unsteady aerodynamics, aeroacoustics and aeroelasticity of turbomachines, DURHAM (USA), 07-11septembre 2003Available from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.2003 n.124 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Investigations of Transonic Aircraft in the Joint DLR / ONERA Project “Non-Linear Aeroelastic Simulation, NLAS II”

The DLR Institute of Aeroelasticity and the ONERA Aeroelasticity and Structural Dynamics Department have a long, proven expertise in the development and the validation of aeroelastic tools for aircraft, and a long-standing cooperation both in experimental and numerical activi-ties. The common project NLAS II (2009-2012) was devoted to the assessment and the vali-dation of numerical aeroelastic technologies developed and used at the respective institutes of DLR and ONERA to simulate and predict the aeroelastic stability and response of aircraft in transonic flow. For that purpose, both partners could take advantage of high quality wind tunnel data availa-ble at the partners for the validation of the numerical approaches. Four common test cases covering a range of challenging and relevant physical phenomena have been selected. The phenomena include static coupling for the prediction of steady state flow and steady state wing deformation, as well as dynamic coupling for transonic flutter and Limit Cycle Oscilla-tions (LCO). Analyses both in the time domain and in the frequency domain have been undertaken, per-forming a wide range of Euler, RANS and URANS calculations. DLR used an aeroelastic process chain based on the TAU code, ONERA used the aeroelastic extension elsA/Ael of the elsA software. Static coupling results, unsteady forced motion computations for 2D and 3D flap motions, and dynamic coupling simulations for the prediction of Limit Cycle Oscillations are presented