Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings

Balducchi, Franck; Arghir, Mihaï; Gauthier, Romain

doi:10.1115/1.4031409

Cited by 27 publications

(21 citation statements)

References 18 publications

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“…Breakthroughs in materials and manufacturing technology reported in the late 1990s/early 2000s have intensified research into its applicability to an ever increasing range of turbomachinery [2]. However, the analysis of FAB-rotor systems presents a challenging nonlinear problem that discourages their use [3]. As stated by Balducchi et al [3], the designer is not only faced with a bearing that is considerably more complex than traditional journal bearings, but experimental results show nonlinear phenomena that cannot be predicted with traditional theoretical models based on linear rotordynamic coefficients.…”

Section: Introductionmentioning

confidence: 99%

An experimental and theoretical analysis of a foil-air bearing rotor system

Bonello

Hassan

2018

Journal of Sound and Vibration

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Although there is considerable research on the experimental testing of foil-air bearing (FAB) rotor systems, only a small fraction has been correlated with simulations from a full nonlinear model that links the rotor, air film and foil domains, due to modelling complexity and computational burden. An approach for the simultaneous solution of the three domains as a coupled dynamical system, introduced by the first author and adopted by independent researchers, has recently demonstrated its capability to address this problem. This paper uses this approach, with further developments, in an experimental and theoretical study of a FAB-rotor test rig. The test rig is described in detail, including issues with its commissioning.The theoretical analysis uses a recently introduced modal-based bump foil model that accounts for interaction between the bumps and their inertia. The imposition of pressure constraints on the air film is found to delay the predicted onset of instability speed. The results lend experimental validation to a recent theoretically-based claim that the Gümbel condition may not be appropriate for a practical singlepad FAB. The satisfactory prediction of the salient features of the measured nonlinear behavior shows that the air film is indeed highly influential on the response, in contrast to an earlier finding.

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Section: Introductionmentioning

confidence: 99%

An experimental and theoretical analysis of a foil-air bearing rotor system

Bonello

Hassan

2018

Journal of Sound and Vibration

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“…11 More recently, the non-linear characteristics of the bump foil have been experimentally examined. [12][13][14][15] More accurate bump foil models have also been developed that are better at predicting non-linear bump foil behaviour. 16 Traditional dynamic analyses of rotors supported by AFBs are based on linearised aerodynamic and friction forces, i.e.…”

Section: Introductionmentioning

confidence: 99%

Transient and steady state behaviour of elasto–aerodynamic air foil bearings, considering bump foil compliance and top foil inertia and flexibility: A numerical investigation

Nielsen

Santos

2017

Proceedings of the Institution of Mechanical Engineers, Part J:

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This work gives a theoretical contribution to the problem of modelling air foil bearings considering large sagging effects in the calculation of the non-linear transient and steady state response of a rigid rotor. This paper consists of two parts: the development of a miltiphysics model of the air foil bearing, and a numerical parameter study of a rigid journal supported in an air foil bearing with a partially supported top foil. The mathematical model of the air foil bearing is centred around the finite element models of both the air film and the top foil structure. These finite element models utilise two types of eight-node isoparametric elements. The rotor is modelled as a rigid body without rotational inertia, i.e. as a journal. The bump foil is included via a bilinear version of the simple elastic foundation model. This paper introduces the bilinear simple elastic foundation model, which combined with the top foil structure model, enables a separation of the top foil and the bump foil. A phenomenon associated within areas of the top foil is where the aerodynamic pressure is sub-ambient. The parameter study investigates the performance of three air foil bearings with partially supported top foils and one air foil bearing with a fully supported top foil. The steady state responses of a journal supported by these air foil bearings are investigated for varied rotational speeds and journal unbalances as well as the top foil sagging in the unsupported area. The study reveals that sub-harmonic vibrations associated with a large journal unbalance can be eliminated by a proper design layout of the bump foil, i.e. placement of the unsupported area. The positive effect is attributed to ‘equivalent shallow pockets’ formed by the sagging top foil.

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“…These vibrations occur at Chair of Engineering Design and Product Reliability, Berlin Institute of Technology, Germany higher rotor speeds, due to self-excitations, 1 and poor balanced systems. [2][3][4][5][6][7] The use of structural modifications on the elastic structure can avoid or decrease these vibrations. [2][3][4] In Hoffmann et al 1 the source of the sub-synchronous vibrations is analysed.…”

Section: Introductionmentioning

confidence: 99%

A valid method of gas foil bearing parameter estimation: A model anchored on experimental data

Hoffmann

Munz

Pronobis

et al. 2016

Proceedings of the Institution of Mechanical Engineers, Part C:

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Gas foil bearings are a smart green technology and suitable for the next generation of small turbo machinery e.g. turbochargers, micro gas turbines, range extenders and compressors of fuel cells. A combination of low power loss, high speed operation and the omission of an oil system are the major advantages. To enable access to this technology, it is essential to evaluate critical speeds and onset speeds of subharmonic vibration of the rotor system in the first design stage. Hence, robust and valid models are necessary, which correctly describe the fluid structure interaction between the lubrication film and the elastic bearing structure. In the past three decades several experimental and numerical investigations of bearing parameters have been published. But the number of sophisticated models is small and there is still a lack of validation towards experimental works. To make it easy for designers dealing with this issue, the bearing parameters are often linearised about certain operating points. In this paper a method for calculating linearised bearing parameters (stiffness and damping) of gas foil bearing is presented. Experimental data are used for validation of the model. The linearised stiffness and damping values are calculated using a perturbation method. The pressure field is coupled with a two-dimensional plate model, while the non-linear bump structure is simplified by a link-spring model. It includes Coulomb friction effects inside the elastic corrugated structure and captures the interaction between the single bumps. For solving the separated perturbed Reynolds equation a static stiffness is used for the 0. order equation (stationary case) and a dynamic stiffness is applied for 1. order equation (dynamic case). Therefore, an additional dynamic structural model is applied to calculate the dynamic stiffness. The results depend on the load level and friction state of each bump. Different case studies including the impact of clearance, frictional contacts and the comparison of a linear and non-linear structure are carried out for infinitesimal perturbations. The results show, that the linear structure underestimates main and cross-coupling effects. The impact of the clearance is notable, while the impact of the overall frictional contacts is small due to relatively small loadings. The infinitely small perturbation model is adapted to the experimental setup by using a superposition of two resulting bearing parameters identifications of two total loadings including shaker forces. Due to this adaptation a good correlation with the experimental results of the bearing parameters is achieved.

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Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings

Cited by 27 publications

References 18 publications

An experimental and theoretical analysis of a foil-air bearing rotor system

An experimental and theoretical analysis of a foil-air bearing rotor system

Transient and steady state behaviour of elasto–aerodynamic air foil bearings, considering bump foil compliance and top foil inertia and flexibility: A numerical investigation

A valid method of gas foil bearing parameter estimation: A model anchored on experimental data

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