Hubert Schwarze

Numerical Simulation of Surface Roughness Effects in Laminar Lubrication Using the Lattice-Boltzmann Method

The effect of surface texture and roughness on shear and pressure forces in tribological applications in the lubrication regime is analyzed by means of lattice-Boltzmann simulations that take the geometry of real surface elements into account. Topographic data on representative surface structures are obtained with high spatial resolution with the application of an optical interference technique. The three-dimensional velocity field past these surfaces is computed for laminar flow of Newtonian fluids in the continuum regime. Subsequently, pressure and shear flow factors are obtained by evaluating the velocity field in accordance with the extended Reynolds equation of Patir and Cheng (1978, ASME J. Tribal., 100, pp. 12-17). The approach allows an efficient determination of the hydrodynamic characteristics of microstructured surfaces in lubrication. Especially, the influence of anisotropy of surface texture on the hydrodynamic load capacity and friction is determined. The numerical method used in the present work is verified for a simplified model configuration, the flow past a channel with sinusoidal walls. The results obtained indicate that full numerical simulations should be used to accurately and efficiently compute the characteristic properties of film flows past rough surfaces and may therefore contribute to a better understanding and prediction of tribological problems.

Auswirkung von Ethanol E85 auf Schmierstoffalterung und Verschleiss im Ottomotor

Die Auswirkung von ethanolhaltigem Kraftstoff auf die Schmierolalterung in Ottomotoren ist bisher kaum untersucht. Das FVV-Forschungsprojekt 930 von TU Clausthal, Universitat Kassel und IFOS Kaiserslautern zeigt auf, dass der Betrieb mit E85 die Lebensdauer des Motors verkurzt. Fur die Steuerkette als Triboleitsystem erhoht sich die Verschleisrate um 20 %.

Measurement and Prediction of the Static Operating Conditions of a Large Turbine Tilting-Pad Bearing Under High Circumferential Speeds and Heavy Loads

The identification results for the static performance characteristics of a large tilting-pad bearing in load between pad configuration are presented for specific bearing loads between 1.0 and 2.5 MPa and for circumferential speeds up to 79 m/s. The bearing is lubricated by spray-bars and can be described by the following specifications: Five pads, 0.23 nominal preload, 60% offset, 56° pad arc angle, 500 mm inner diameter, 350 mm pad length and 1.28 per mille relative bearing clearance. The axial oil flow is reduced by a fixed seal on both bearing edges which has a nominal radial clearance of 1 mm. The film pressure and the gap width are determined in the whole area of the sliding surface by an axial shift of the shaft. The bearing temperatures are measured by means of 100 thermocouples located 5 mm behind the sliding surface. The experimental results indicate that significant pad deformation occurs in circumferential and in axial direction. Also the effective supply temperatures are much higher than the nominal ones. According to the lubricant flow the sensor temperatures close to the spray-bars at the sliding surface rise about 20 K for 7 l/s and 40 K for 3.5 l/s at 3000 rpm. The temperatures are nearly constant between all pads and depend only on speed and not on load.The theoretical analyses of the bearing performance was accomplished with the bearing calculation software COMBROS. This code models the transition between laminar and turbulent flow and solves an extended Reynolds equation, the three dimensional energy equation of the film and the heat conduction equations of the shaft and the pads considering various boundary conditions due to the judgment of the user. Concerning the minimum film thickness, the maximum temperature on the sliding surface and the maximum film pressure only poor agreement was reached if the influence of the axial pad deformation was neglected. In advanced analyses a co-simulation between COMBROS and a structural mechanics software shows that an improvement of the prediction was achieved. The comparison of the measurement data and the advanced simulation shows very good agreement for the characteristic bearing parameters as well as for the local distributions of film pressure, temperature and film thickness in the whole operating range of the bearing. Further, the applied inlet mixing model for the lubricant supply process proves to be very suitable.Copyright

Predictions for run-up procedures of automotive turbochargers with full-floating ring bearings including thermal effects and different bearing setups

Automotive turbochargers feature a variety of boundary conditions influencing the operating behaviour during run-up procedures. As a novel aspect the influence of the thrust bearing and load on lateral vibration phenomena is investigated in detail for this application. The run-up predictions show that the thrust bearing and load have significant influence on the frequencies as well as on the magnitudes of the vibrations. In particular, the amplitudes of conical vibrational modes are damped. Further, the consideration of the hot gas boundary conditions is identified as decisive in order to predict the bearing parameters and consequently the vibrations precisely.

Ölalterung und Verschleiß im Ottomotor

Aus Grunden des Umweltschutzes und der Servicefreundlichkeit ist die Automobilindustrie bestrebt, die Olwechsel-intervalle zu optimieren. Im Auftrag der Forschungsvereinigung Verbrennungskraftmaschinen e. V. (FVV) haben drei Forschungspartner in einem gemeinsamen Forschungsprojekt die Schmierstoffalterung und deren Einfluss auf das Verschleisverhalten der Tribosysteme im Ottomotor untersucht. Die Partner sind das Institut fur Tribologie und Energiewandlungsmaschinen der Technischen Universitat Clausthal, das Institut fur Maschinenelemente und Konstruktionstechnik der Universitat Kassel und das Institut fur Oberflachen- und Schichtanalytik GmbH der Technischen Universitat Kaiserslautern.

The Impact of Convective Fluid Inertia Forces on Operation of Tilting-Pad Journal Bearings

This paper presents a combination of experimental data, CFD analyses, and bearing code predictions on emergence of convective inertia fluid forces within the lube oil flow of tilting-pad journal bearings. Concordantly, experimental data and CFD analyses show a significant rise of local pressure at the transition between inlet and leading edge of tilting-pad, especially for high-speed applications with surface speeds up to 100 m/s. This effect can be related to convective inertia forces within fluid flow as cross-sections and flow character rapidly change at the pad entrance. An energy-based approach is implemented in the bearing code in order to provide enhanced boundary conditions for Reynolds equation considering this effect. As a result, predictions of bearing code achieved significant improved correlation with measured pressure distributions and CFD-data. Further, beside the local influence, a nonnegligible impact on characteristic parameters of bearing operation such as maximum temperature and stiffness and damping coefficients is observed. Finally, the results are critically analyzed and requirements to gain more distinct and reliable data are specified.

Thermal analysis of small high-speed floating-ring journal bearings

In the present paper, the impact of thermal boundary conditions on characteristic parameters of full floating-ring journal bearings (FRB) typically used in small automotive turbochargers (TC) is discussed. A complex thermo-hydrodynamic simulation model is introduced which is validated by experimental data under real TC operating conditions on a hot-gas test stand. The conducted study clarifies the significant impact of the shaft temperature on overall bearing operating parameters which cannot be neglected. Compared to using an adiabatic shaft model, the accuracy of ring-speed prediction is considerably improved by a non-adiabatic approach.

Lubricant degradation and wear behaviour in a spark-ignition engine

For protecting the environment and increasing convenience in service, the automotive industry is endeavouring to optimise the oil-change intervals. On behalf of the German Research Association for Combustion Engines (FVV), three research partners have investigated the degradation of lubricants and its effect on the wear behaviour of the tribo-systems in a spark-ignition engine in the course of a joint research project. The partners are the Institute of Tribology and Energy Conversion Machinery at Clausthal University of Technology, the Institute of Machine Elements and Design Engineering at University of Technology Kassel, and the Institute of Surface and Coating Analysis at University of Technology Kaiserslautern.

A Theoretical Study on Frequency Effects on Tilting-Pad Journal Bearing Dynamic Coefficients

The quantitative impact of pivot position, pivot support stiffness, and deformation on frequency dependency of a stiffness (K) and damping (C) KC matrix model for tilting-pad journal bearings is investigated. A theoretical model for prediction of frequency influences is introduced neglecting inertia effects. Predictions based on this model are validated with test data taken from literature. The results achieve good agreement with experimental data. A sensitivity analysis is performed providing the following key results: (i) all three investigated parameters possibly exhibit non negligible frequency influences, (ii) significant misinterpretations are possible if single influencing parameters on the operation conditions are disregarded or only roughly estimated, (iii) a frequency independent KCM model is suitable for off-center pivot position and sub-synchronous frequency ratios, (iv) a state-space model separating rotor and pad movement is necessary to model all theoretical possible effects by a linear model with frequency independent coefficients for a certain rotor speed.

Lubricants and the Lubrication System

Diesel engines not impose make maximum demands on the loading capacity of every component but also on the lubricant , i.e. the engine oil , which is therefore a technically complex operating agent [11-1–11-3]. Since the operating conditions of car and commercial vehicle diesel engines and large diesel engines differ considerably, differently optimized lubricating oils are employed for the intended purposes.