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Chasalevris A.,BorgWarner Turbo Systems Engineering GmbH | Chasalevris A.,Alstom
Journal of Tribology | Year: 2015

The three-lobe bearings widely used in rotating machinery follow the design data evaluated using numerical methods for the solution of the Reynolds equation. This paper defines exact and approximate analytical solutions of the Reynolds equation for the case of three-lobe bearings with finite length. Dynamic characteristics are provided analytically with closed-form expressions for laminar regimes of operation, using an approximate analytical solution that proves to be reliable and of low cost of evaluation time. The results for eccentricity ratio, equilibrium locus, stiffness and damping coefficients are presented for a range of Sommerfeld number and different cases of load orientation and compared with theoretical and experimental data from the literature. Copyright © 2015 by ASME. Source

Gugau M.,BorgWarner Turbo Systems Engineering GmbH | Roclawski H.,University of Kaiserslautern
Journal of Engineering for Gas Turbines and Power | Year: 2014

With emission legislation becoming more stringent within the next years, almost all future internal combustion gasoline engines need to reduce specific fuel consumption, most of them by using turbochargers. Additionally, car manufactures attach high importance to a good drivability, which usually is being quantified as a target torque already available at low engine speeds - reached in transient response operation as fast as possible. These engine requirements result in a challenging turbocharger compressor and turbine design task, since for both not one single operating point needs to be aerodynamically optimized but the components have to provide for the optimum overall compromise for maximum thermodynamic performance. The component design targets are closely related and actually controlled by the matching procedure that fits turbine and compressor to the engine. Inaccuracies in matching a turbine to the engine full load are largely due to the pulsating engine flow characteristic and arise from the necessity of arbitrary turbine map extrapolation toward low turbine blade speed ratios and the deficient estimation of turbine efficiency for low engine speed operating points. This paper addresses the above described standard problems, presenting a methodology that covers almost all aspects of thermodynamic turbine design based on a comparison of radial and mixed-flow turbines. Wheel geometry definition with respect to contrary design objectives is done using computational fluid dynamics (CFD), finite element analysis (FEA), and optimization software. Parametrical turbine models, composed of wheel, volute, and standard piping allow for fast map calculation similar to steady hot gas tests but covering the complete range of engine pulsating mass flow. These extended turbine maps are then used for a particular assessment of turbine power output under unsteady flow admission resulting in an improved steady-state matching quality. Additionally, the effect of various design parameters like either volute sizing or the choice of compressor to turbine diameter ratio on turbine blade speed ratio operating range as well as well as turbine inertia effect is analyzed. Finally, this method enables the designer to comparatively evaluate the ability of a turbine design to accelerate the turbocharger speed for transient engine response while still offering a map characteristic that keeps fuel consumption low at all engine speeds. © 2014 by ASME. Source

Nagode M.,University of Ljubljana | Langler F.,BorgWarner Turbo Systems Engineering GmbH | Hack M.,LMS Deutschland
International Journal of Fatigue | Year: 2011

The damage operator approach is extended to time dependent viscoplasticity and creep. The oxidation is taken into account indirectly. Time efficient viscoplastic approximation based on the nonlinear Maxwell model and the corresponding lifetime prediction is presented. Both thermo-mechanical fatigue tests on the specimens and the thermal shock tests on turbine housings of a turbocharger subject to a complex change of temperature and strain are conducted for identification and verification purposes. The material is casting material Ni-resist D-5S. The research points out that the mean stress correction and the multiaxial criterion affect the predictive lifetimes significantly. For the turbine housing of a turbocharger the Smith-Watson-Topper mean stress correction, tensile-compressive creep and the critical plane mode I approach is the most suitable parameter combination. The lifetime predictions are convenient. The time consuming elastoviscoplastic finite element analyses can thus often be replaced by the elastoplastic FEA with kinematic hardening even at extreme conditions. © 2010 Elsevier Ltd. All rights reserved. Source

Koutsovasilis P.,BorgWarner Turbo Systems Engineering GmbH | Schweizer B.,TU Darmstadt
Archive of Applied Mechanics | Year: 2014

The modeling and simulation process of oil-film bearing dynamics constitutes a rather essential task integrated in the workflow of various mechanical products. Specifically, in the turbo charger industry, the correct capture and understanding of the associated nonlinear rotating dynamics is of utmost importance, since the system's efficiency and lifetime span depends on it. The root cause of the nonlinear rotordynamic effects is the oil-film concentrated in the rotor's journal bearings. Its behavior is highly coupled with both the system's geometric and dynamic configuration. The dynamics of the oil-film are described by the well-known Navier-Stokes equation, which under a series of assumptions and simplifications results to the, so-called, Reynolds equation. In this paper, the Reynolds equation is numerically solved based on a finite difference scheme and several parameter variation studies are conducted in an effort to pinpoint the most influential parameters - journal bearing geometric dimensions, oil-film properties and rotor-velocity-driven inputs - with respect to designated responses - friction, oil-film pressure force, minimum oil-film thickness and boundary oil-flow - all of which are regarded as important in terms of the aforementioned system's efficiency and lifetime span. Based on multivariate analysis algorithms, correlation outcomes and global sensitivity results are presented. In an effort to capture possible nonlinear phenomena, which might not be possible via linear data mining tools, the Spearman rank-order coefficient and self-organizing maps methodology are applied. © 2014 Springer-Verlag Berlin Heidelberg. Source

Nagode M.,University of Ljubljana | Langler F.,BorgWarner Turbo Systems Engineering GmbH | Hack M.,LMS Deutschland
Engineering Failure Analysis | Year: 2011

The turbine housing of a turbocharger is exposed to extensive cyclic thermo-mechanical loading. This leads to a major challenge to design the turbine housing in order to ensure its guaranteed lifetime in relation to the high temperature behaviour of the material. The first step is to develop and validate a damage operator based lifetime calculation approach together with a constitutive material model for application on the casting material Ni-resist D-5S. A satisfactory prediction of the number of cycles until crack initiation by considering fatigue and creep damage is demonstrated on specimens subject to characteristic loading conditions and further on the critical positions of turbine housings, respectively. © 2011 Elsevier Ltd. Source

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