Mihai Arghir

Mihai Arghir
Institut Pprime | Institut P’ · Génie Mécanique et Systèmes Complexes

PhD

About

137
Publications
8,648
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1,242
Citations

Publications

Publications (137)
Article
A steady-state one-dimensional axisymmetric numerical model of a mechanical seal in two-phase flow is presented. In this work a non-linear thermal model is implemented using a coupled (monolithic) approach, linking the fluid film and sealing rings. It is solved for the temperature fields of the fluid and solids, heat fluxes between fluids and solid...
Conference Paper
Full-text available
The present study is focused on the design and use of an ElectroMagnetic Actuator (EMA) for the experimental identification of cylindrical and tilting pad journal bearings rotordynamic coefficients. First, the experimental apparatus is described, then the force-current formulation controlling the EMA is adapted and experimentally validated using th...
Article
The present work presents a comparison between the homogenization and the multiscale methods applied to the compressible Reynolds equation with irregular coefficients. The equation models a very thin compressible flow between rough surfaces. If the use of the homogenization method for the Reynolds equation with irregular coefficients is not new, it...
Article
The present work deals with the thermogasodynamic analysis of the segmented annular seal provided with Rayleigh pockets. The paper is a continuation of the work presented Arghir, M., and Mariot, A. (2017, “Theoretical Analysis of the Static Characteristics of the Carbon Segmented Seal,” ASME J. Tribol., 139(6), p. 062202.) where an isothermal model...
Article
A segmented annular seal is composed of several identical carbon segments assembled around the rotor by a circumferential (garter) spring. Each segment has one or more pads delimited by deep grooves to generate a radial lift force when the speed of rotation is not zero. One of the solutions for enhancing this lift is to provide inclined grooves on...
Chapter
The present work deals with experimental measurements of rotordynamic force coefficients for two types of impellers: open (unshrouded) and closed (front shrouded). The impellers were designed to work in a turbopump with a cryogenic fluid, but experiments were performed in a test rig where water is used as working fluid. All the tests were conducted...
Article
The Morton effect is a thermally induced increase of synchronous vibrations amplitudes of rotors. The shearing of the fluid film in a journal bearing produces an asymmetric heating of the rotor which causes its thermal bending and increases the unbalance. The vector of synchronous vibrations describes a spiral with slowly increasing amplitude and p...
Conference Paper
This paper presents a stability analysis of the Morton effect. The analysis is an extension of the Murphy and Lorenz method [11] and is based on better estimates of three influence coefficients linking the phenomena contributing to the Morton effect: the total response to the rotor unbalance, the temperature difference on the rotor surface induced...
Article
The present work presents the numerical investigation of the bump height manufacturing errors on the unbalance response of an aerodynamic foil journal bearing. This is the first study of the impact of manufacturing errors based on an important number of samples. A statistical analysis predicts the mean values of the characteristics and the standard...
Article
The present work presents the experimental analyses of a rigid (short) and of a flexible (long) rotor subject to thermal unbalance effects. The rotors are supported by a ball bearing and by a cylindrical journal bearing. The differential heating generated in the journal bearing is responsible for the thermal unbalance. The results obtained with the...
Poster
Full-text available
This poster presents the test rig and the main results of the studies on the Morton effect with flexible rotor and a flexure pivot tilting pad journal bearing. Since the conference, an extension of these results have been published in the MSSP journal.
Article
The paper presents a new structural bump foil model that can handle all operating conditions from start-up to full speed. The model is based on a non-linear contact algorithm with friction and gaps. The model considers the gaps between the bump foil and the bearing casing, between the bump foil and the top foil and between the rotor and the top foi...
Conference Paper
Full-text available
The paper presents a new structural bump foil model that can handle all operating conditions from start-up to full speed. The model is based on a non-linear contact algorithm with friction and gaps. The top foil is modeled as a curved beam while bump foil uses a coupled truss model. The model considers the gaps between the bump foil and the bearing...
Conference Paper
A radial segmented seal is composed of three or six carbon segments that are assembled by a circumferential (garter) spring that presses them against the rotor. Assembled, they take the form of an annular ring. Each segment has several pads that generate a radial lift force depending on the rotor speed. There are many ways of creating effective lif...
Article
The paper introduces a structural model for bump-type foil bearings based on contact mechanics including gaps and friction. The starting point is a model introduced in [32] were the bump foil is approximated by a specific structure of interacting springs. Following this model, contacts between the top and bump foils and between the bump foil and th...
Presentation
The paper presents the synchronous amplitudes of unbalance responses of a rigid rotor supported by an aerodynamic foil bearing and a ball bearing. The foil bearing is affected by bump height manufacturing errors. The paper describes the main points of the theoretical model dealing with foil manufacturing errors. The model is based on contact mechan...
Chapter
The present paper presents experimental measurements of rotordynamic force coefficients for a multistage arrangement of four identical brush seals. The bristles are metallic, with a lay angle of 50° from radial centerline and have an initial radial interference with the shaft of 0.12 mm. According to a radial feeding groove, two pairs of two seals...
Chapter
The present work tackles the dead band clearance problem of rotors guided by ball or roller bearings. There are situations when the rotor can be only temporary in contact with the casing. The closed-loose nature of the rotor-stator contact leads to a non-linear rotordynamic response. A test rig dedicated to the experimental analysis of this problem...
Chapter
The present work tackles the impact of manufacturing errors on the unbalance response of a Jeffcott rotor supported on aerodynamic foil bearings. The peculiarity of the model is the use of the Abaqus software for describing the dynamic response of the foil structure, for calculating the thin film pressures and for integrating the equations of motio...
Article
Full-text available
The present work is focused on the numerical solution of the complete energy equation used in fluid film lubrication. The work was motivated by the fact that the complete energy equation has no analytical solution that can be used for validations. Its accuracy and computation time are related to the employed numerical method and to the grid resolut...
Preprint
The present work is focused on the numerical solution of the complete energy equation used in fluid film lubrication. The work was motivated by the fact the complete energy equation has no analytic solution that could be used for validations. Its accuracy and computation time are related to the employed numerical method and to the grid resolution....
Article
The paper presents the experimental results obtained for brush seals of 38 mm diameter operating with air at pressure differences up to 7 bars and rotation frequencies up to 500 Hz. The seals had bristles of 70 μm diameter, made of Haynes 25. Seals with two radial interferences (0 and 100 μm) between the brush and the rotor were tested. The present...
Article
This work presents the comparison between experimental and theoretical results obtained for three straight annular seals. One of the annular seals has smooth rotor and stator while the others have a textured stator; the textures are equally spaced shallow round holes, with two different depths. The experimental results were obtained on a test rig d...
Poster
Full-text available
A test rig was developed for underlining the large amplitude synchronous vibrations induced by journal asymmetric heating in an oil lubricated journal bearing. The test rig consists of an overhung rotor supported at its drive end by a ball bearing and at its opposite end by a cylindrical journal bearing. A disk is mounted at the non-drive end of th...
Article
Brush seals are a mature technology that has generated extensive experimental and theoretical work. Theoretical models range from simple correlations with experimental results to advanced numerical approaches coupling the bristles deformation with the flow in the brush. The present work follows this latter path. The bristles of the brush are deform...
Article
The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings are problems that are the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foi...
Article
Counter-rotation angled injection employed for aerostatic hybrid bearings reduces the cross coupling stiffness that may lead to whirl-whip instabilities at high rotation speeds. The benefits of counter-rotation injection have been known for years. Theoretical investigations were performed for water or air fed hybrid bearings but experiments were co...
Conference Paper
Full-text available
L'étude de la stabilité des rotors supportés par des paliers à feuilles dépend fortement des caractéristiques mécaniques de ces paliers. Plusieurs modèles de la structure souple et compliante existent. Ces modèles se divisent en deux parties, celles qui la modélisent par un ensemble de raideurs indépendantes les unes des autres et celles qui prenne...
Conference Paper
The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings is a problem that is the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foil...
Conference Paper
Counter-rotation angled injection employed for aerostatic hybrid bearings reduces the cross coupling stiffness that may lead to whirl-whip instabilities at high rotation speeds. The benefits of counter-rotation injection have been known for years. Theoretical investigations were performed for water or air fed hybrid bearings but experiments were co...
Article
The segmented carbon seal is regularly used for sealing bearing chambers of aeronautical turboengines or as part of a buffer seal in space turbopumps. The seal operates with contaminated air or with an inert gas and is made of many identical carbon segments (generally three or six) with reciprocally overlapping ends. The segments are pressed agains...
Conference Paper
The present work tackles the dead band clearance problem of rotors guided by ball or roller bearings. There are situations when the rotor can be only temporary in contact with the casing. The closed-loose nature of the rotor-stator contact leads to a non-linear rotordynamic response. A test rig dedicated to the experimental analysis of this problem...
Conference Paper
Full-text available
Les joints à brosse représentent une technologie qui a maintenant une place bien définie dans la conception des machines tournantes où ils peuvent remplacer les étanchéités à labyrinthes. Cependant leur impact sur la dynamique du rotor de la machine tournante est peu connu voir ignoré car la brosse du joint est un élément difficile à modéliser théo...
Conference Paper
The segmented carbon seal is regularly used for sealing bearing chambers of aeronautical turboengines or as part of a buffer seal in space turbopumps. The seal operates with contaminated air or with an inert gas and is made of many identic carbon segments (generally three or six) with reciprocally overlapping ends. The segments are serrated against...
Article
A simplified, new method for evaluating the nonlinear fluid forces in air bearings was recently proposed in [1]. The method is based on approximating the frequency dependent linearized dynamic coefficients at several eccentricities, by second order rational functions. A set of ordinary differential equations is then obtained using the inverse of La...
Article
The present work is focused on the pneumatic hammer instability in an aerostatic bearing with shallow recesses and orifices of four different diameters. Operating conditions were zero rotation speed, zero load, and different supply pressures. The diameters of the tested orifices were large compared to the usual practice and correspond to a combined...
Article
The paper presents the experimental unbalance response of two slightly different rigid rotors supported by two identical aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly on the outer surface entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measure...
Article
Floating ring annular seals represent one of the solutions for controlling leakage in high-speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditi...
Article
Experimental results indicating negative direct static stiffness of highly eccentric straight gas annular seals were very recently presented in [1] by Childs and Arthur. This instability occurred at zero rotation speed and at high eccentricities. Up to then only gas annular seals with zero rotation speed, operating in centered position and with cho...
Article
The present work introduces a numerical model for squeeze film dampers (SFD) operating simultaneously with vapor cavitation and air ingestion. The pressure is given by the Reynolds equation. The vapor cavitation model used in this work is based on Rayleigh-Plesset equation and was previously presented. Air ingestion occurring in open end SFD is dea...
Article
This paper deals with the experimental analysis of the dynamic characteristics of a foil thrust bearing (FTB) designed according to specifications given by NASA scientists in 2009 (Dykas et al., 2009, "Design, Fabrication, and Performance of Foil Gas Thrust Bearings for Microturbomachinery Applications," ASME J. Eng. Gas Turbines Power, 131(1), p....
Article
Vertical turbines installed in hydroelectric dams and guided by hydrodynamic cylindrical journal bearings may suffer from sub-synchronous vibrations. This is especially true when the rotor, the bearings and the seals are perfectly aligned. When present, the sub-synchronous vibrations have large amplitudes and generally limit the rotation speed of t...
Article
Floating ring annular seals represent one of the solutions for controlling leakage in high speed rotating machinery. Low leakage is ensured by the small radial clearance. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor are prohibite...
Article
Aerodynamic foil bearings are highly non linear components used or intending to be used for supporting high speed rotors (>30 krpm) of low size rotating machines (<400 kW). The non linear character comes from the highly deformable structure of the bearing made of thin steel sheets and from the Coulomb friction forces arising during dynamic displace...
Article
Full-text available
The dynamic behavior of rotors is highly influenced by bearing characteristics. In previous works, the authors have shown that it may be beneficial to adapt the bearing behavior to the shaft behavior. Several adaptive and active components will be developed in this paper in order to control the shaft dynamical amplitude. Different models of hydrody...
Conference Paper
The present work presents the comparison between experimental and theoretical results obtained for three straight annular seals. One of the annular seals has smooth rotor and stator while the others have a textured stator; the textures are equally spaced shallow round holes, with two different depths. The experimental results were obtained on a tes...
Article
The present work deals with the numerical analysis of phase change effects and choked flow on the rotordynamic coefficients of cryogenic annular seals. The analysis is based on the "bulk flow" equations, with the energy equation written for the total enthalpy, and uses an estimation of the speed of sound that is valid for single-or two-phase flow a...
Article
This study deals with the experimental results obtained for a hydrostatic/hydrodynamic bearing used in aerospace turbopumps. This supporting element, if fitted with angled injection directed against shaft rotation, can provide a stabilizing effect to the rotor by reducing the circumferential flow. In order to characterize this effect and to improve...
Article
The paper deals with the experimental analysis of the torque and of the lift-off velocity of a foil thrust bearing. The geometric characteristics of the foil thrust bearing follow the design recently proposed by Dykas et al. (2009, "Design, Fabrication, and Performance of Foil Gas Thrust Bearings for Microturbomachinery Applications," ASME J. Eng....
Conference Paper
A simplified nonlinear transient analysis method for gas bearings was recently published by the authors [1]. The method uses the fact that linearized dynamic characteristics of gas bearings, namely the impedances, can be approximated by rational transfer functions. The method gave good results if the rational transfer function approach approximated...
Conference Paper
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
Conference Paper
Hybrid journal bearings are considered since many years as a possible replacement for ball bearings in turbo-pumps used by the aerospace industry. Due to flow regimes dominated by inertia and due to the nature of the lubricant (cryogenic fluids), the prediction of the linearized dynamic coefficients in these bearings must be based on the compressib...
Article
In order to avoid contact between the vibrating rotor and the stator, annular seals are designed with a relatively large radial clearance (similar to 100 mu m) and, therefore, have an important leakage. The floating ring annular seal is able to reduce the leakage flow rate by using a much lower clearance. The seal is designed as a ring floating on...
Article
This study develops the use of an impact hammer as an excitation source for identifying the dynamic coefficients of cylindrical aerodynamic bearings. The test rig and the identification method were originally developed for being used with two electromagnetic shakers applying non-synchronous excitations. The test rig is of a floating bearing type wh...
Article
The traditional small perturbation method is successfully used for linear dynamic analysis of gas bearings but excludes any nonlinear study. Investigating large displacements requires the evaluation of the nonlinear aerodynamic forces in the thin film. To avoid solving the unsteady compressible thin film fluid equations, we propose a method based o...
Article
Full-text available
For some applications it must be considered that the flow in the annular seal contains a mixture of liquid and gas. The multiphase character of the flow is described by the volume fraction of gas (usually air) contained in the liquid under the form of bubbles. The fluid is then a homogenous mixture of air and liquid all thru the annular seal. Its l...
Conference Paper
The dynamic characteristics of a hybrid aerostatic bearing are experimentally investigated on a test rig consisting of a rigid rotor driven by an impulse turbine located at its midlength. The rotor is horizontally mounted and is supported by two identical aerostatic bearings at its ends. Both the impulse turbine and the aerostatic hybrid bearings a...
Article
Full-text available
Le papier présente deux installations expérimentales pour la caractérisation d’un palier à feuilles. La première installation expérimentale est destinée à la mesure du couple de démarrage du palier chargé. La deuxième a pour but la mesure des caractéristiques dynamiques du palier. Les deux installations sont construites sur le principe d’un coussin...
Article
The paper presents the experimental work developed by the authors for the identification of rotordynamic coefficients of air bearings. Air bearings work at very high rotation speeds and are known to have nonlinear dynamic characteristics depending at least on the excitation frequency. The paper presents two very similar test rigs, the testing proce...
Conference Paper
The paper presents the results of the experimental analysis of static and dynamic characteristics of a generation 1 foil bearing of 38.1 mm diameter and L/D = 1. The test rig is of floating bearing type, the rigid shaft being mounted on ceramic ball bearings and driven up to 40 krpm. Two different casings are used for start-up and for measurement o...
Article
The present work contains a detailed presentation of a test rig for measuring the static and dynamic characteristics of air bearings. The test rig consists of a 60-krpm spindle entraining a shaft guided by a Lomakin hybrid bearing. The test bearing is floating, overhung at one end of the shaft, and mounted on a squirrel cage. The bearing is statica...
Article
The article presents the numerical adaptation of the “bulk flow” model for the analysis of squeeze-film dampers of industrial design. These components are characterized by high squeeze Reynolds numbers and by complex feeding and sealing systems. The “bulk flow” system of the equation is an efficient model for dealing with high Reynolds number regim...
Article
In lubricated contacts, the fluid film protects and separates the two contacting surfaces. Depending on the pressure and on the surface velocities, different lubricated regimes can occur. These different lubricated regimes are successively described and some pictures show their occurrence in different contacts.
Article
The present Note deals with the effects of compressibility on the linearized dynamic characteristics of gas lubricated mechanical components (journal and thrust bearings). Although the effect of compressibility on the static characteristics is well known, its influence on the dynamic characteristics is still not clearly understood. The present Note...
Article
This work is intended to evaluate a cavitation model based on the complete Rayleigh-Plesset (RP) equation for use in squeeze film damper calculations. The RP equation governs the variation in the radius of the cavitation bubbles at rest, surrounded by an infinite incompressible fluid and subjected to an external pressure. This equation is obtained...
Article
A gas bearing of bump-type foil comprises an underlying structure made of one or several strips of corrugated sheet metal covered by a top foil surface. The fluid film pressure thus needs to be coupled with the behavior of this structure for obtaining the equivalent bearing characteristics. The dynamic model of the bump-type foil structure is then...
Article
In order to reduce the embarked mass, the new designs of turbojet engines use softened rotors working with higher speeds. Following this trend, the use of intershaft bearings in dual-spool turbojets is then recommended for reducing weight. However, due to residual unbalances present in both rotors, the intershaft bearing is submitted to hard workin...
Conference Paper
In this presentation we will first show historical pictures concerning friction and wear since the earlier ages. Next we shall present some pictures concerning different sorts of surface damage including abrasive and adhesive wear, scuffing, fretting corrosion, corrosive wear, wear due to over-heating in lubricated contacts, cavitation erosion, fat...
Conference Paper
One of the main interests of gas foil bearings lies in their superior rotordynamic characteristics compared to conventional bearings. A numerical investigation on the stability limit and on the unbalanced response of foil bearings is presented in this paper. The main difficulty in modeling the dynamic behavior of such bearings comes from the dry fr...
Article
In this presentation we will first show historical pictures concerning friction and wear since the earlier ages. Next we shall present some pictures concerning different sorts of surface damage including abrasive and adhesive wear, scuffing, fretting corrosion, corrosive wear, wear due to over-heating in lubricated contacts, cavitation erosion, fat...
Conference Paper
The present work presents a bulk flow based numerical analysis of squeeze film dampers (SFD) provided with circumferential grooves, feeding orifices and piston ring sealing devices. This means that the bulk flow model for inertia dominated flow regimes (high Re) was adapted for taking into account thin film discontinuities, mass sources located in...
Article
The paper deals with the static stability of annular gas seals under choked flow conditions. For a centered straight annular seal choking can occur only in the exit section because the gas is constantly accelerated by friction forces. From the mathematical standpoint, the flow choking corresponds to a singularity that was never dealt with numerical...
Article
A gas bearing of bump foil type comprises an underlying structure made of one or several strips of corrugated sheet metal covered by a top foil surface. The fluid film pressure needs to be coupled with the behavior of the structure for obtaining the whole bearing characteristics. Unlike in classical elasto-aerodynamic models, a foil bearing (FB) st...
Article
The present work presents a new theoretical approach for the analysis of textured annular “damper” seals. The data for the seal were extracted from the work of Childs and Fayolle [1]. The texture of the stator consists of equally spaced cylindrical holes of an order of magnitude larger than the seal clearance. The main idea of the present work is t...
Article
The performance of Gas Foil Bearings (GFBs) relies on a coupling between a thin gas film and an elastic structure with dissipative characteristics. Due to the mechanical complexity of the structure, the evaluation of its stiffness and damping is still largely inaccurate if not arbitrary. The goal of this paper is to improve the understanding of the...
Conference Paper
A dynamic model of the bump-type foil bearing structure is presented in this paper. This model is an extension of a static model that considers the corrugated foil as a multidegree of freedom system. The system of differential equations describing the dynamic displacements is obtained by considering the global stiffness matrix of the structure and...
Article
Les principaux modèles structurels d'un palier à feuilles présents dans la littérature considèrent les ondulations du plissé comme des ressorts indépendants. Ces modèles permettent une implémentation relativement simple dans un code de calcul de paliers à gaz. Ils permettent également la prise en compte d'un coefficient d'amortissement de la struct...
Article
The classical theory of hydrodynamic lubrication assumes that the flow regime is laminar and the inertia forces in the fluid film are negligible. For large bearings using low viscosity lubricant or for high speed, the inertia forces could be important and non laminar flow occurs. In that presentation a general view of non-laminar lubrication is pre...
Article
The present work deals with several aspects of the finite-volume numerical solution of the Reynolds equation for a compressible fluid. First, the upwind procedure used for stabilizing the solution is given a new interpretation. It is shown next how film thickness discontinuities can be handled in a mathematically correct way and finally, the finite...
Article
The present work introduces the main results of a detailed experimental program aimed at investigating the influence of the design parameters and of the working conditions on the global characteristics of squeeze film dampers (SFD) for serial aircraft engines. The SFD is sealed at both ends and is executing circular centered orbits. The results are...
Article
The present work deals with the flow characteristics induced by a two-dimensional roughness pattern. The roughness pattern consists of identical and equally spaced rectangles with characteristic lengths at least one order of magnitude larger than the clearance of the thin film. Periodic boundary conditions enable the analysis of a single groove and...
Conference Paper
This work is an overview of theoretical approaches used for estimating the characteristics of straight or grooved annular seals. The flow in annular seals is dominated by inertia forces. The goal of the static analysis is to describe the relation between the pressure difference across the seal and the (mass) flow rate. The presentation introduces d...
Article
This work presents a thin film flow model for analyzing the static and dynamic characteristics of centered, eccentric or misaligned tangential-against-rotation injection Lomakin bearings. The Lomakin bearing is a recent device intended for use in modern turbomachinery and having characteristics similar to hybrid bearings. It can be described as an...
Article
The present paper is a synthesis of the work performed by the authors on the problems characterising the high Reynolds number lubrication namely the turbulent flow regime and the presence of inertia effects. The paper introduces the first approach of the turbulent regime based on the mixing length concept and shows how the Reynolds equation was mod...